14 ms·

Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on userns mounts

110 points by Valmar 8y ago

PavlovsCat 8y ago
I'm not a kernel dev, I hardly know what the kernel is, but even I know this by now.. if a change breaks something in user space, it's always a kernel bug.
- iforgotpassword 8y ago
  Yeah that Eric guy really needs to read Linus' mail to Mauro.
  - icebraining 8y ago
    Or Linus' mail to himself: https://lkml.org/lkml/2012/3/8/495 https://lkml.org/lkml/2012/3/8/495
    - PavlovsCat 8y ago
      I love how he ends all that with "Really." In my books, Linus was always alright, but I like more polite yet firm Linus even more. Best of both worlds. Merry Christmas to Linus and all Linux contributors (!), and thanks for one of the greatest gifts of modern time.
    - acqq 8y ago
      I really like: „We're not masturbating around with some research project. We never were. Even when Linux was young, the whole and only point was to make a usable system. It's why it's not some crazy drug-induced microkernel or other random crazy thing.“ It‘s too direct but easily understandable.
    - klagermkii 8y ago
      Interesting to see the difference in style of old Linus vs new reformed Linus. Seems like the new style comes across as just heavily disappointed and with a breach of trust, which I guess compared to the plain anger of old is easier to convey without swearing and vivid imagery. I think I personally would still prefer to receive one of the old style messages, but that's probably just because I better handle people angry with me than disappointed.
      - Semaphor 8y ago
        I agree. I read this and thought it was really depressing. And I'm not even the person this was targeted at.
        philwelch 8y ago
        A classic Linus rant has all the same basic information ("backwards compatibility is the first rule of kernel maintenance", "you've been a contributor long enough that you should know this", "I'm reverting your changes and no longer accepting pull requests from you"), but it also has the added comic relief of Linus swearing and ranting. Take away the swearing and ranting and this is just uncomfortable to read.
      - newnewpdro 8y ago
        > I better handle people angry with me than disappointed. This, so much this. I was raised in a hot-headed european household where people would get angry and argue energetically, often using coarse language. It clearly demonstrated care, passion, and a willingness and desire to continue suffering together. The low-energy disappointed response sends a very different message. It's probably my upbringing, but it leaves me feeling like the collaboration is over and I should pack up my things.
      - philwelch 8y ago
        > I think I personally would still prefer to receive one of the old style messages, but that's probably just because I better handle people angry with me than disappointed. That's actually not that unusual. I actually found this email a lot harsher, in a certain sense. When you losing your temper and swear at people, it's scary and intimidating because the hindbrain recognizes that behavior as, "this person is very likely to hit me". And since hindbrains are hindbrains, this reaction still happens even if it's over the internet. But you also end up making a big fool of yourself and leading people to discount what you're saying out of hand, because obviously you're angry and worked up. People losing their temper are hilarious from a safe distance, which is among other things the basic premise of Lewis Black's entire career as a comedian. When you calmly and methodically communicate using only facts and logic, you do lose the hindbrain "this guy is going to hit me" reaction. But you get something more powerful. Heated anger indicates an unresolved problem. That's why you're all worked up--you have a nice little adrenaline rush going because you've detected a problem and you're fired up to go fix it. Being calm, even cold, is much more final: it indicates that everything is resolved. This approach completely disarms the defense mechanism of saying "Linus is just a dick" or thinking that he only said what he said out of anger.
- geofft 8y ago
  The funny thing is that you've got that drilled into your head even though it's not true. Userspace breaks all the time, it's just that some of them matter to Linus and some don't, and he's never been clear about which is which. Several months ago at work I found a vendor app that was calling listen(0), i.e., listen for up to 0 connections, and worked fine on older kernels because they rounded to a minimum of 8. Newer kernels stopped doing that. Nobody cared. Nobody got criticized, constructively or unconstructively. (By the time we noticed it was several kernel releases upstream so bringing it up would just be asking for another change to userspace.) Linus himself broke userspace once in the hope nobody would notice. Spoiler: they did. https://lkml.org/lkml/2017/5/29/541 https://lkml.org/lkml/2017/5/29/541 And that's not counting all the things that aren't part of the stable interface like procfs and sysfs nodes, device names, etc. There is a clear version of what Linus is trying to say. He's just never said it.
  - xani 8y ago
    So your point is that if you don't report breakage it won't get fixed ?
raverbashing 8y ago
A bit offtopic, but it seems the issues the kernel is handling are getting even more esoteric Iteractions between different permissions and conditions is getting ever more complex But yeah, kernel shouldn't break userspace, and this should have been internalized already by the maintainers
- stestagg 8y ago
  Strengthening controls on a system while simultaneously not breaking any client is an incredibly difficult goal. Unfortunately, unless there is a single, united team focussed on this single goal (kernel is not by design). Then some fingers will be burned, because of the complexity of getting it right. Some contributors will struggle, and others will fail at it. Unfortunately, that’s just stats.
  - hedora 8y ago
    The systemd and various “secure” linux teams keep adding poorly thought out access controls that no one understands, that have escoteric loopholes and break things in terrible ways. I wish they’d just move back to the original unix permission scheme, plus jails. BSD and solaris did much better jobs of this a decade ago. Hopefully one of those will eventually take over again.
    - JdeBP 8y ago
      Solaris and (some of) the BSDs have NFS-style ACLs, and do not have the original Unix permission scheme either.
Havoc 8y ago
Haha well at least he isn't cursing anymore
- mmirate 8y ago
  Only time will tell whether that change is for better or for worse. (Unless your chosen metric-of-value relies on feelings instead of actual concrete results.)
  - tyingq 8y ago
    I like the new tone. It is clear and conveys severity/urgency without the swearing and personal attacks. Compare to: https://lkml.org/lkml/2012/3/8/495 https://lkml.org/lkml/2012/3/8/495 That's the same guy, so clearly, the swearing didn't have much lasting effect :)
    - mmirate 8y ago
      That's one person of many. And it's not a question of aesthetics of the message in the short term, but of the quality of the overall results in the long term and the effort needed to achieve them. Hopefully this won't happen, but it's entirely possible that this change will result in Linus finding himself with a much greater number of broken, half-broken and/or subtly-broken PRs to review than ever before, increasing the chances of something like https://lwn.net/Articles/57135/ https://lwn.net/Articles/57135/ succeeding. And having a kernel backdoor ship worldwide is way worse than having a few recalcitrant kernel developers be exposed to - oh no! - coarse language. Results > the "fee fees".
      - saagarjha 8y ago
        Are you saying that Linus has been able to review fewer patches because his personality has driven people away, and by being nicer he’d be overwhelmed trying to review code?
        mmirate 8y ago
akerl_ 8y ago
I think this email underscores something people miss when discussing Linus's communication style. It is entirely possible, as we see here, to convey the criticality of something without crossing over into personal attacks.
- mmirate 8y ago
  Convey to us reasonable people, reading it at a distance as 3rd-parties? Absolutely. ... Convey to the intended recipient, with his inevitable personal/emotional/etc. attachments to the topic, in such a way that it takes the intended effect? A pending question-of-fact, and one that can only be answered very indirectly and in the long run. Heck, if the answer really is "no", then it's possible we may never know! (until the NSA pwns us all, or at least pwns the subset of us who didn't kowtow to whoever the central socio-econo-political authority of that era will be)
  - akerl_ 8y ago
    I don't think it's actually a pending question whether avoiding personal attacks makes people more likely to listen to a message.
    - kryogen1c 8y ago
      > I don't think it's actually a pending question whether avoiding personal attacks makes people more likely to listen to a message. That depends on the context. When you're talking about changing ingrained behaviors, emotional shock and awe can definitely be necessary and the shortest, most painless path to resolution. the underlying incorrect assumption is that everyone will do the right thing, if only nicely and logically talked to. This is not true and obvious to anyone with experience managing large amounts of people, especially so when firing is not an easy option.
      - darpa_escapee 8y ago
        > the underlying incorrect assumption is that everyone will do the right thing, if only nicely and logically talked to. This is not true and obvious to anyone with experience managing large amounts of people, especially so when firing is not an easy option. I've yet to see abusive management tactics work in the long term. It might work in the short term, but people with the means will take it as a signal to jump ship because no adult is going to accept abuse if they don't have to. I've heard your exact sentiment echoed by people who aspire towards management, and it always comes across as a weird power trip fantasy.
ivraatiems 8y ago
I've been extremely critical of Linus Torvalds in the past. I was glad to see him decide publicly to change his behavior, and I am glad to see him doing better here. Personally, I think this level of disappointment/anger/trust issue would be best dealt with face-to-face or via a phone or Skype call, or at least an off-list email. However, given the unique situation of the Linux kernel, I think it was appropriate to send to the public list. The only line I'd remove or finesse is "Yeah, this is complete garbage." Otherwise, I think this is a great example of how to convey anger without personally attacking anyone. Linus doesn't swear, he doesn't call Eric stupid or curse him out, but he still says what he means: The behavior was out of line, it has to stop, and, most importantly, it represents a breach of trust. He's not saying Eric is a bad, stupid or worthless person - he is saying that in this instance, Eric's behavior is bad. That's the key difference.
- polishTar 8y ago
  Eh it’s better, but don’t kid yourself, it’s still pretty terrible. Still too aggressive, still too personal. The reprimand part of this email really shouldn’t have been made public. The tone used was not necessary to convey the ideas he was trying to communicate. Don’t get me wrong, the lack of direct insults/namecalling is definitely an improvement, but I’d personally still hate to work with someone who chooses to communicate to their subordinates this way.
  - Valmar 8y ago
    This is better than his old style. If Linus doesn't put his trusted submaintainers into line, they'll think they can violate core rules of kernel maintenance ~ something as bad breaking userspace. Linus was right to reply exactly the way he did for such breakage. There's nothing terrible about reprimanding someone you trusted, especially in front of everyone else. Helps to tell people to not repeat this level of mistake.
- philwelch 8y ago
  > The only line I'd remove or finesse is "Yeah, this is complete garbage." Otherwise, I think this is a great example of how to convey anger without personally attacking anyone. The basic principle that I think Linus is trying to follow is, "criticize the <subject matter>, not the person" (whether you're criticizing someone's ideas, someone's work, or someone's behavior). Linus isn't saying that Eric is complete garbage, he's saying that a specifically quoted statement is complete garbage for reasons that he expands on later. I have seen things like this interpreted as personal attacks before, even though they don't actually parse out that way logically, but for someone (like me) who has to learn these rules instead of instinctively knowing them by feel, this is an easy mistake to make.
philwelch 8y ago
Damn, cold-bloodedly nice Linus is terrifying.
- mikeash 8y ago
  Indeed. I think this illustrates that being civil is not just about making people more comfortable, it’s also more effective.
OnlyRepliesToBS 8y ago
linus is stability
Arnavion 8y ago
Heh, I know of one time the kernel did break backward-compatibility, intentionally even - https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38514d66591ae728b778e3b https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38... My fan controller used the sysfs paths mentioned in the commit message directly. So while the commit is probably correct that users of the lm-sensors library would not be affected, my application was. It was relatively easy to fix since I was the only user of the application, so I didn't care about being compatible with older kernels.
ec109685 8y ago
This attitude is what has allowed Linux containers to work as well as they do. You can put software built and tested on a very old kernel and it runs successfully on a modern one. Container operators do not have to deeply worry that every kernel update will break all their developer’s applications.
- greenyoda 8y ago
  This attitude is what allows any operating system to be usable. Nobody would want to develop code under Windows (or buy that code) if they knew that it would break when the user moved from Windows 7 to Windows 10. In the IBM mainframe world, people can still run code written in the 1960s (without even recompiling it). If Linus didn't fanatically enforce backward compatibility, nobody could rely on Linux for mission-critical systems.
  - ec109685 8y ago
    There were BC breaks across Mac OS X’s kernel. Windows does a good job keeping things backwards compatible as well.
- geofft 8y ago
  > You can put software built and tested on a very old kernel and it runs successfully on a modern one. This is factually untrue. CentOS 5's glibc makes system calls using the vsyscall page, which is off by default in e.g. Debian stable kernels because it's a huge security risk (it's a page at a fixed address that makes syscalls, it's an obvious ROP target and makes ASLR completely irrelevant, and it also contains fixed data so it's a useful target for other attacker-controlled pointers too). So CentOS 5 containers do not run on up-to-date Debian systems unless you reboot and change a kernel option. I think vsyscalls are on by default in Linus's tree but no distributor is gonna turn them on and take the security risk. The knob was put there so it could be turned off.
jrwr 8y ago
I've got a good one, I found a Kernel Bug in the memory manager of all places by being a tryhard in mergerfs (and upstream fuse was broken as well) http://lkml.iu.edu/hypermail/linux/kernel/1610.0/00878.html http://lkml.iu.edu/hypermail/linux/kernel/1610.0/00878.html

110 points by Valmar 8y ago

I'm not a kernel dev, I hardly know what the kernel is, but even I know this by now.. if a change breaks something in user space, it's always a kernel bug.

iforgotpassword 8y ago
Yeah that Eric guy really needs to read Linus' mail to Mauro.
- icebraining 8y ago
  Or Linus' mail to himself: https://lkml.org/lkml/2012/3/8/495 https://lkml.org/lkml/2012/3/8/495
  - PavlovsCat 8y ago
    I love how he ends all that with "Really." In my books, Linus was always alright, but I like more polite yet firm Linus even more. Best of both worlds. Merry Christmas to Linus and all Linux contributors (!), and thanks for one of the greatest gifts of modern time.
  - acqq 8y ago
    I really like: „We're not masturbating around with some research project. We never were. Even when Linux was young, the whole and only point was to make a usable system. It's why it's not some crazy drug-induced microkernel or other random crazy thing.“ It‘s too direct but easily understandable.
  - klagermkii 8y ago
    Interesting to see the difference in style of old Linus vs new reformed Linus. Seems like the new style comes across as just heavily disappointed and with a breach of trust, which I guess compared to the plain anger of old is easier to convey without swearing and vivid imagery. I think I personally would still prefer to receive one of the old style messages, but that's probably just because I better handle people angry with me than disappointed.
    - Semaphor 8y ago
      I agree. I read this and thought it was really depressing. And I'm not even the person this was targeted at.
      - philwelch 8y ago
        A classic Linus rant has all the same basic information ("backwards compatibility is the first rule of kernel maintenance", "you've been a contributor long enough that you should know this", "I'm reverting your changes and no longer accepting pull requests from you"), but it also has the added comic relief of Linus swearing and ranting. Take away the swearing and ranting and this is just uncomfortable to read.
    - newnewpdro 8y ago
      > I better handle people angry with me than disappointed. This, so much this. I was raised in a hot-headed european household where people would get angry and argue energetically, often using coarse language. It clearly demonstrated care, passion, and a willingness and desire to continue suffering together. The low-energy disappointed response sends a very different message. It's probably my upbringing, but it leaves me feeling like the collaboration is over and I should pack up my things.
    - philwelch 8y ago
      > I think I personally would still prefer to receive one of the old style messages, but that's probably just because I better handle people angry with me than disappointed. That's actually not that unusual. I actually found this email a lot harsher, in a certain sense. When you losing your temper and swear at people, it's scary and intimidating because the hindbrain recognizes that behavior as, "this person is very likely to hit me". And since hindbrains are hindbrains, this reaction still happens even if it's over the internet. But you also end up making a big fool of yourself and leading people to discount what you're saying out of hand, because obviously you're angry and worked up. People losing their temper are hilarious from a safe distance, which is among other things the basic premise of Lewis Black's entire career as a comedian. When you calmly and methodically communicate using only facts and logic, you do lose the hindbrain "this guy is going to hit me" reaction. But you get something more powerful. Heated anger indicates an unresolved problem. That's why you're all worked up--you have a nice little adrenaline rush going because you've detected a problem and you're fired up to go fix it. Being calm, even cold, is much more final: it indicates that everything is resolved. This approach completely disarms the defense mechanism of saying "Linus is just a dick" or thinking that he only said what he said out of anger.
geofft 8y ago
The funny thing is that you've got that drilled into your head even though it's not true. Userspace breaks all the time, it's just that some of them matter to Linus and some don't, and he's never been clear about which is which. Several months ago at work I found a vendor app that was calling listen(0), i.e., listen for up to 0 connections, and worked fine on older kernels because they rounded to a minimum of 8. Newer kernels stopped doing that. Nobody cared. Nobody got criticized, constructively or unconstructively. (By the time we noticed it was several kernel releases upstream so bringing it up would just be asking for another change to userspace.) Linus himself broke userspace once in the hope nobody would notice. Spoiler: they did. https://lkml.org/lkml/2017/5/29/541 https://lkml.org/lkml/2017/5/29/541 And that's not counting all the things that aren't part of the stable interface like procfs and sysfs nodes, device names, etc. There is a clear version of what Linus is trying to say. He's just never said it.
- xani 8y ago
  So your point is that if you don't report breakage it won't get fixed ?

raverbashing 8y ago

A bit offtopic, but it seems the issues the kernel is handling are getting even more esoteric Iteractions between different permissions and conditions is getting ever more complex But yeah, kernel shouldn't break userspace, and this should have been internalized already by the maintainers

stestagg 8y ago
Strengthening controls on a system while simultaneously not breaking any client is an incredibly difficult goal. Unfortunately, unless there is a single, united team focussed on this single goal (kernel is not by design). Then some fingers will be burned, because of the complexity of getting it right. Some contributors will struggle, and others will fail at it. Unfortunately, that’s just stats.
- hedora 8y ago
  The systemd and various “secure” linux teams keep adding poorly thought out access controls that no one understands, that have escoteric loopholes and break things in terrible ways. I wish they’d just move back to the original unix permission scheme, plus jails. BSD and solaris did much better jobs of this a decade ago. Hopefully one of those will eventually take over again.
  - JdeBP 8y ago
    Solaris and (some of) the BSDs have NFS-style ACLs, and do not have the original Unix permission scheme either.

Havoc 8y ago

Haha well at least he isn't cursing anymore

mmirate 8y ago
Only time will tell whether that change is for better or for worse. (Unless your chosen metric-of-value relies on feelings instead of actual concrete results.)
- tyingq 8y ago
  I like the new tone. It is clear and conveys severity/urgency without the swearing and personal attacks. Compare to: https://lkml.org/lkml/2012/3/8/495 https://lkml.org/lkml/2012/3/8/495 That's the same guy, so clearly, the swearing didn't have much lasting effect :)
  - mmirate 8y ago
    That's one person of many. And it's not a question of aesthetics of the message in the short term, but of the quality of the overall results in the long term and the effort needed to achieve them. Hopefully this won't happen, but it's entirely possible that this change will result in Linus finding himself with a much greater number of broken, half-broken and/or subtly-broken PRs to review than ever before, increasing the chances of something like https://lwn.net/Articles/57135/ https://lwn.net/Articles/57135/ succeeding. And having a kernel backdoor ship worldwide is way worse than having a few recalcitrant kernel developers be exposed to - oh no! - coarse language. Results > the "fee fees".
    - saagarjha 8y ago
      Are you saying that Linus has been able to review fewer patches because his personality has driven people away, and by being nicer he’d be overwhelmed trying to review code?
      - mmirate 8y ago

akerl_ 8y ago

I think this email underscores something people miss when discussing Linus's communication style. It is entirely possible, as we see here, to convey the criticality of something without crossing over into personal attacks.

mmirate 8y ago
Convey to us reasonable people, reading it at a distance as 3rd-parties? Absolutely. ... Convey to the intended recipient, with his inevitable personal/emotional/etc. attachments to the topic, in such a way that it takes the intended effect? A pending question-of-fact, and one that can only be answered very indirectly and in the long run. Heck, if the answer really is "no", then it's possible we may never know! (until the NSA pwns us all, or at least pwns the subset of us who didn't kowtow to whoever the central socio-econo-political authority of that era will be)
- akerl_ 8y ago
  I don't think it's actually a pending question whether avoiding personal attacks makes people more likely to listen to a message.
  - kryogen1c 8y ago
    > I don't think it's actually a pending question whether avoiding personal attacks makes people more likely to listen to a message. That depends on the context. When you're talking about changing ingrained behaviors, emotional shock and awe can definitely be necessary and the shortest, most painless path to resolution. the underlying incorrect assumption is that everyone will do the right thing, if only nicely and logically talked to. This is not true and obvious to anyone with experience managing large amounts of people, especially so when firing is not an easy option.
    - darpa_escapee 8y ago
      > the underlying incorrect assumption is that everyone will do the right thing, if only nicely and logically talked to. This is not true and obvious to anyone with experience managing large amounts of people, especially so when firing is not an easy option. I've yet to see abusive management tactics work in the long term. It might work in the short term, but people with the means will take it as a signal to jump ship because no adult is going to accept abuse if they don't have to. I've heard your exact sentiment echoed by people who aspire towards management, and it always comes across as a weird power trip fantasy.

ivraatiems 8y ago

I've been extremely critical of Linus Torvalds in the past. I was glad to see him decide publicly to change his behavior, and I am glad to see him doing better here. Personally, I think this level of disappointment/anger/trust issue would be best dealt with face-to-face or via a phone or Skype call, or at least an off-list email. However, given the unique situation of the Linux kernel, I think it was appropriate to send to the public list. The only line I'd remove or finesse is "Yeah, this is complete garbage." Otherwise, I think this is a great example of how to convey anger without personally attacking anyone. Linus doesn't swear, he doesn't call Eric stupid or curse him out, but he still says what he means: The behavior was out of line, it has to stop, and, most importantly, it represents a breach of trust. He's not saying Eric is a bad, stupid or worthless person - he is saying that in this instance, Eric's behavior is bad. That's the key difference.

polishTar 8y ago
Eh it’s better, but don’t kid yourself, it’s still pretty terrible. Still too aggressive, still too personal. The reprimand part of this email really shouldn’t have been made public. The tone used was not necessary to convey the ideas he was trying to communicate. Don’t get me wrong, the lack of direct insults/namecalling is definitely an improvement, but I’d personally still hate to work with someone who chooses to communicate to their subordinates this way.
- Valmar 8y ago
  This is better than his old style. If Linus doesn't put his trusted submaintainers into line, they'll think they can violate core rules of kernel maintenance ~ something as bad breaking userspace. Linus was right to reply exactly the way he did for such breakage. There's nothing terrible about reprimanding someone you trusted, especially in front of everyone else. Helps to tell people to not repeat this level of mistake.
philwelch 8y ago
> The only line I'd remove or finesse is "Yeah, this is complete garbage." Otherwise, I think this is a great example of how to convey anger without personally attacking anyone. The basic principle that I think Linus is trying to follow is, "criticize the <subject matter>, not the person" (whether you're criticizing someone's ideas, someone's work, or someone's behavior). Linus isn't saying that Eric is complete garbage, he's saying that a specifically quoted statement is complete garbage for reasons that he expands on later. I have seen things like this interpreted as personal attacks before, even though they don't actually parse out that way logically, but for someone (like me) who has to learn these rules instead of instinctively knowing them by feel, this is an easy mistake to make.

philwelch 8y ago

Damn, cold-bloodedly nice Linus is terrifying.

mikeash 8y ago
Indeed. I think this illustrates that being civil is not just about making people more comfortable, it’s also more effective.

OnlyRepliesToBS 8y ago

linus is stability

Arnavion 8y ago

Heh, I know of one time the kernel did break backward-compatibility, intentionally even - https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38514d66591ae728b778e3b https://github.com/torvalds/linux/commit/6b99e3569ba17b9fd38... My fan controller used the sysfs paths mentioned in the commit message directly. So while the commit is probably correct that users of the lm-sensors library would not be affected, my application was. It was relatively easy to fix since I was the only user of the application, so I didn't care about being compatible with older kernels.

ec109685 8y ago

This attitude is what has allowed Linux containers to work as well as they do. You can put software built and tested on a very old kernel and it runs successfully on a modern one. Container operators do not have to deeply worry that every kernel update will break all their developer’s applications.

greenyoda 8y ago
This attitude is what allows any operating system to be usable. Nobody would want to develop code under Windows (or buy that code) if they knew that it would break when the user moved from Windows 7 to Windows 10. In the IBM mainframe world, people can still run code written in the 1960s (without even recompiling it). If Linus didn't fanatically enforce backward compatibility, nobody could rely on Linux for mission-critical systems.
- ec109685 8y ago
  There were BC breaks across Mac OS X’s kernel. Windows does a good job keeping things backwards compatible as well.
geofft 8y ago
> You can put software built and tested on a very old kernel and it runs successfully on a modern one. This is factually untrue. CentOS 5's glibc makes system calls using the vsyscall page, which is off by default in e.g. Debian stable kernels because it's a huge security risk (it's a page at a fixed address that makes syscalls, it's an obvious ROP target and makes ASLR completely irrelevant, and it also contains fixed data so it's a useful target for other attacker-controlled pointers too). So CentOS 5 containers do not run on up-to-date Debian systems unless you reboot and change a kernel option. I think vsyscalls are on by default in Linus's tree but no distributor is gonna turn them on and take the security risk. The knob was put there so it could be turned off.

jrwr 8y ago

I've got a good one, I found a Kernel Bug in the memory manager of all places by being a tryhard in mergerfs (and upstream fuse was broken as well) http://lkml.iu.edu/hypermail/linux/kernel/1610.0/00878.html http://lkml.iu.edu/hypermail/linux/kernel/1610.0/00878.html