* [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() [not found] <20190109074524.10176-1-kjlu@umn.edu> @ 2019-01-21 11:32 ` tip-bot for Kangjie Lu 2019-01-27 11:04 ` Thomas Gleixner 0 siblings, 1 reply; 6+ messages in thread From: tip-bot for Kangjie Lu @ 2019-01-21 11:32 UTC (permalink / raw) To: linux-tip-commits Cc: linux-kernel, peterz, torvalds, tglx, hpa, stable, mingo, kjlu Commit-ID: 120e4e76857ddbc9268e1aa3f9de61a498e84618 Gitweb: https://git.kernel.org/tip/120e4e76857ddbc9268e1aa3f9de61a498e84618 Author: Kangjie Lu <kjlu@umn.edu> AuthorDate: Wed, 9 Jan 2019 01:45:24 -0600 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Mon, 21 Jan 2019 11:26:17 +0100 sched/core: Fix a potential double-fetch bug in sched_copy_attr() "uattr->size" is copied in from user space and checked. However, it is copied in again after the security check. A malicious user may race to change it. The fix sets uattr->size to be the checked size. Signed-off-by: Kangjie Lu <kjlu@umn.edu> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: pakki001@umn.edu Cc: <stable@vger.kernel.org> Link: https://lkml.kernel.org/r/20190109074524.10176-1-kjlu@umn.edu Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/sched/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a674c7db2f29..d4d3514c4fe9 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a if (ret) return -EFAULT; + /* In case attr->size was changed by user-space: */ + attr->size = size; + /* * XXX: Do we want to be lenient like existing syscalls; or do we want * to be strict and return an error on out-of-bounds values? ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() 2019-01-21 11:32 ` [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() tip-bot for Kangjie Lu @ 2019-01-27 11:04 ` Thomas Gleixner 2019-01-27 11:28 ` Ingo Molnar 2019-01-28 7:58 ` Peter Zijlstra 0 siblings, 2 replies; 6+ messages in thread From: Thomas Gleixner @ 2019-01-27 11:04 UTC (permalink / raw) To: mingo, kjlu, hpa, stable, peterz, torvalds, linux-kernel Cc: linux-tip-commits On Mon, 21 Jan 2019, tip-bot for Kangjie Lu wrote: > Commit-ID: 120e4e76857ddbc9268e1aa3f9de61a498e84618 > Gitweb: https://git.kernel.org/tip/120e4e76857ddbc9268e1aa3f9de61a498e84618 > Author: Kangjie Lu <kjlu@umn.edu> > AuthorDate: Wed, 9 Jan 2019 01:45:24 -0600 > Committer: Ingo Molnar <mingo@kernel.org> > CommitDate: Mon, 21 Jan 2019 11:26:17 +0100 > > sched/core: Fix a potential double-fetch bug in sched_copy_attr() > > "uattr->size" is copied in from user space and checked. However, it is > copied in again after the security check. A malicious user may race to > change it. The fix sets uattr->size to be the checked size. > > Signed-off-by: Kangjie Lu <kjlu@umn.edu> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: pakki001@umn.edu > Cc: <stable@vger.kernel.org> > Link: https://lkml.kernel.org/r/20190109074524.10176-1-kjlu@umn.edu > Signed-off-by: Ingo Molnar <mingo@kernel.org> > --- > kernel/sched/core.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index a674c7db2f29..d4d3514c4fe9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > if (ret) > return -EFAULT; > > + /* In case attr->size was changed by user-space: */ > + attr->size = size; > + Just when pondering to send that to Linus, I tried to write up a concise summary for this which made me look at the patch. If the size changed, then its clear that user space fiddled with the date between the size fetch and the full copy from user. So why restoring the size instead of doing the obvious: if (attr->size != size) return -ECRAP; Hmm? Thanks, tglx ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() 2019-01-27 11:04 ` Thomas Gleixner @ 2019-01-27 11:28 ` Ingo Molnar 2019-01-28 7:58 ` Peter Zijlstra 1 sibling, 0 replies; 6+ messages in thread From: Ingo Molnar @ 2019-01-27 11:28 UTC (permalink / raw) To: Thomas Gleixner Cc: kjlu, hpa, stable, peterz, torvalds, linux-kernel, linux-tip-commits * Thomas Gleixner <tglx@linutronix.de> wrote: > On Mon, 21 Jan 2019, tip-bot for Kangjie Lu wrote: > > Commit-ID: 120e4e76857ddbc9268e1aa3f9de61a498e84618 > > Gitweb: https://git.kernel.org/tip/120e4e76857ddbc9268e1aa3f9de61a498e84618 > > Author: Kangjie Lu <kjlu@umn.edu> > > AuthorDate: Wed, 9 Jan 2019 01:45:24 -0600 > > Committer: Ingo Molnar <mingo@kernel.org> > > CommitDate: Mon, 21 Jan 2019 11:26:17 +0100 > > > > sched/core: Fix a potential double-fetch bug in sched_copy_attr() > > > > "uattr->size" is copied in from user space and checked. However, it is > > copied in again after the security check. A malicious user may race to > > change it. The fix sets uattr->size to be the checked size. > > > > Signed-off-by: Kangjie Lu <kjlu@umn.edu> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > Cc: Linus Torvalds <torvalds@linux-foundation.org> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Cc: pakki001@umn.edu > > Cc: <stable@vger.kernel.org> > > Link: https://lkml.kernel.org/r/20190109074524.10176-1-kjlu@umn.edu > > Signed-off-by: Ingo Molnar <mingo@kernel.org> > > --- > > kernel/sched/core.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index a674c7db2f29..d4d3514c4fe9 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > > if (ret) > > return -EFAULT; > > > > + /* In case attr->size was changed by user-space: */ > > + attr->size = size; > > + > > Just when pondering to send that to Linus, I tried to write up a concise > summary for this which made me look at the patch. > > If the size changed, then its clear that user space fiddled with the date > between the size fetch and the full copy from user. So why restoring the > size instead of doing the obvious: > > if (attr->size != size) > return -ECRAP; > > Hmm? Yeah, indeed - and that's a much more reliable interface behavior in any case. It's probably also faster. Thanks, Ingo ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() 2019-01-27 11:04 ` Thomas Gleixner 2019-01-27 11:28 ` Ingo Molnar @ 2019-01-28 7:58 ` Peter Zijlstra 2019-01-28 13:15 ` Thomas Gleixner 1 sibling, 1 reply; 6+ messages in thread From: Peter Zijlstra @ 2019-01-28 7:58 UTC (permalink / raw) To: Thomas Gleixner Cc: mingo, kjlu, hpa, stable, torvalds, linux-kernel, linux-tip-commits On Sun, Jan 27, 2019 at 12:04:44PM +0100, Thomas Gleixner wrote: > On Mon, 21 Jan 2019, tip-bot for Kangjie Lu wrote: > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index a674c7db2f29..d4d3514c4fe9 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > > if (ret) > > return -EFAULT; > > > > + /* In case attr->size was changed by user-space: */ > > + attr->size = size; > > + > > Just when pondering to send that to Linus, I tried to write up a concise > summary for this which made me look at the patch. > > If the size changed, then its clear that user space fiddled with the date > between the size fetch and the full copy from user. So why restoring the > size instead of doing the obvious: > > if (attr->size != size) > return -ECRAP; > > Hmm? Sure; but if we do that we should also change perf_copy_attr() which has the exact same thing. ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() 2019-01-28 7:58 ` Peter Zijlstra @ 2019-01-28 13:15 ` Thomas Gleixner 2019-03-10 10:09 ` Thomas Gleixner 0 siblings, 1 reply; 6+ messages in thread From: Thomas Gleixner @ 2019-01-28 13:15 UTC (permalink / raw) To: Peter Zijlstra Cc: mingo, kjlu, hpa, stable, torvalds, linux-kernel, linux-tip-commits On Mon, 28 Jan 2019, Peter Zijlstra wrote: > On Sun, Jan 27, 2019 at 12:04:44PM +0100, Thomas Gleixner wrote: > > On Mon, 21 Jan 2019, tip-bot for Kangjie Lu wrote: > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > index a674c7db2f29..d4d3514c4fe9 100644 > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > > > if (ret) > > > return -EFAULT; > > > > > > + /* In case attr->size was changed by user-space: */ > > > + attr->size = size; > > > + > > > > Just when pondering to send that to Linus, I tried to write up a concise > > summary for this which made me look at the patch. > > > > If the size changed, then its clear that user space fiddled with the date > > between the size fetch and the full copy from user. So why restoring the > > size instead of doing the obvious: > > > > if (attr->size != size) > > return -ECRAP; > > > > Hmm? > > Sure; but if we do that we should also change perf_copy_attr() which has > the exact same thing. Yes please. The point is that by default the data passed to a function (and it does not matter whether it's a syscall) by pointer is immutable. There is exactly ONE syscall which is specifically designed to deal with mutable data and that's a constant source of headache .... Kangjie is right that all double fetch operations like the one in sched_copy_attr() are prone to concurrent modification problems. But then we really should say NO instead of silently trying to fix things up. I personally would even kill the process immediately, no matter whether the corruption is caused by malicious intent or by sheer stupidity. Thanks, tglx ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() 2019-01-28 13:15 ` Thomas Gleixner @ 2019-03-10 10:09 ` Thomas Gleixner 0 siblings, 0 replies; 6+ messages in thread From: Thomas Gleixner @ 2019-03-10 10:09 UTC (permalink / raw) To: Peter Zijlstra Cc: mingo, kjlu, hpa, stable, torvalds, linux-kernel, linux-tip-commits On Mon, 28 Jan 2019, Thomas Gleixner wrote: > On Mon, 28 Jan 2019, Peter Zijlstra wrote: > > On Sun, Jan 27, 2019 at 12:04:44PM +0100, Thomas Gleixner wrote: > > > On Mon, 21 Jan 2019, tip-bot for Kangjie Lu wrote: > > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > > index a674c7db2f29..d4d3514c4fe9 100644 > > > > --- a/kernel/sched/core.c > > > > +++ b/kernel/sched/core.c > > > > @@ -4499,6 +4499,9 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > > > > if (ret) > > > > return -EFAULT; > > > > > > > > + /* In case attr->size was changed by user-space: */ > > > > + attr->size = size; > > > > + > > > > > > Just when pondering to send that to Linus, I tried to write up a concise > > > summary for this which made me look at the patch. > > > > > > If the size changed, then its clear that user space fiddled with the date > > > between the size fetch and the full copy from user. So why restoring the > > > size instead of doing the obvious: > > > > > > if (attr->size != size) > > > return -ECRAP; > > > > > > Hmm? > > > > Sure; but if we do that we should also change perf_copy_attr() which has > > the exact same thing. > > Yes please. > > The point is that by default the data passed to a function (and it does not > matter whether it's a syscall) by pointer is immutable. There is exactly > ONE syscall which is specifically designed to deal with mutable data and > that's a constant source of headache .... > > Kangjie is right that all double fetch operations like the one in > sched_copy_attr() are prone to concurrent modification problems. But then > we really should say NO instead of silently trying to fix things up. I > personally would even kill the process immediately, no matter whether the > corruption is caused by malicious intent or by sheer stupidity. Just noticed that this fell through the cracks. Is anyone working on a fix for this? Thanks, tglx ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-03-10 10:10 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
[not found] <20190109074524.10176-1-kjlu@umn.edu>
2019-01-21 11:32 ` [tip:sched/core] sched/core: Fix a potential double-fetch bug in sched_copy_attr() tip-bot for Kangjie Lu
2019-01-27 11:04 ` Thomas Gleixner
2019-01-27 11:28 ` Ingo Molnar
2019-01-28 7:58 ` Peter Zijlstra
2019-01-28 13:15 ` Thomas Gleixner
2019-03-10 10:09 ` Thomas Gleixner
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).