* Thomas Gleixner <[email protected]> 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 <[email protected]> > > AuthorDate: Wed, 9 Jan 2019 01:45:24 -0600 > > Committer: Ingo Molnar <[email protected]> > > 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 <[email protected]> > > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > > Cc: Linus Torvalds <[email protected]> > > Cc: Peter Zijlstra <[email protected]> > > Cc: Thomas Gleixner <[email protected]> > > Cc: [email protected] > > Cc: <[email protected]> > > Link: https://lkml.kernel.org/r/[email protected] > > Signed-off-by: Ingo Molnar <[email protected]> > > --- > > 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
