This is a note to let you know that I've just added the patch titled
timers: Prevent union confusion from unexpected restart_syscall()
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timers-prevent-union-confusion-from-unexpected-resta.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3c683c46758688b0b24f8123a07a7e22ca57692e
Author: Jann Horn <jannh@xxxxxxxxxx>
Date: Thu Jan 5 14:44:03 2023 +0100
timers: Prevent union confusion from unexpected restart_syscall()
[ Upstream commit 9f76d59173d9d146e96c66886b671c1915a5c5e5 ]
The nanosleep syscalls use the restart_block mechanism, with a quirk:
The `type` and `rmtp`/`compat_rmtp` fields are set up unconditionally on
syscall entry, while the rest of the restart_block is only set up in the
unlikely case that the syscall is actually interrupted by a signal (or
pseudo-signal) that doesn't have a signal handler.
If the restart_block was set up by a previous syscall (futex(...,
FUTEX_WAIT, ...) or poll()) and hasn't been invalidated somehow since then,
this will clobber some of the union fields used by futex_wait_restart() and
do_restart_poll().
If userspace afterwards wrongly calls the restart_syscall syscall,
futex_wait_restart()/do_restart_poll() will read struct fields that have
been clobbered.
This doesn't actually lead to anything particularly interesting because
none of the union fields contain trusted kernel data, and
futex(..., FUTEX_WAIT, ...) and poll() aren't syscalls where it makes much
sense to apply seccomp filters to their arguments.
So the current consequences are just of the "if userspace does bad stuff,
it can damage itself, and that's not a problem" flavor.
But still, it seems like a hazard for future developers, so invalidate the
restart_block when partly setting it up in the nanosleep syscalls.
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230105134403.754986-1-jannh@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 94dd37e8890d8..7a84c54219f35 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1564,6 +1564,7 @@ SYSCALL_DEFINE2(nanosleep, struct timespec __user *, rqtp,
if (!timespec64_valid(&tu))
return -EINVAL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_NATIVE : TT_NONE;
current->restart_block.nanosleep.rmtp = rmtp;
return hrtimer_nanosleep(&tu, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
@@ -1582,6 +1583,7 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp,
if (!timespec64_valid(&tu))
return -EINVAL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_COMPAT : TT_NONE;
current->restart_block.nanosleep.compat_rmtp = rmtp;
return hrtimer_nanosleep(&tu, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
diff --git a/kernel/time/posix-stubs.c b/kernel/time/posix-stubs.c
index 06f34feb635ed..20117340c2493 100644
--- a/kernel/time/posix-stubs.c
+++ b/kernel/time/posix-stubs.c
@@ -136,6 +136,7 @@ SYSCALL_DEFINE4(clock_nanosleep, const clockid_t, which_clock, int, flags,
return -EINVAL;
if (flags & TIMER_ABSTIME)
rmtp = NULL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_NATIVE : TT_NONE;
current->restart_block.nanosleep.rmtp = rmtp;
return hrtimer_nanosleep(&t64, flags & TIMER_ABSTIME ?
@@ -222,6 +223,7 @@ COMPAT_SYSCALL_DEFINE4(clock_nanosleep, clockid_t, which_clock, int, flags,
return -EINVAL;
if (flags & TIMER_ABSTIME)
rmtp = NULL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_COMPAT : TT_NONE;
current->restart_block.nanosleep.compat_rmtp = rmtp;
return hrtimer_nanosleep(&t64, flags & TIMER_ABSTIME ?
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index f46694850b445..8b90abd690730 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -1227,6 +1227,7 @@ SYSCALL_DEFINE4(clock_nanosleep, const clockid_t, which_clock, int, flags,
return -EINVAL;
if (flags & TIMER_ABSTIME)
rmtp = NULL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_NATIVE : TT_NONE;
current->restart_block.nanosleep.rmtp = rmtp;
@@ -1253,6 +1254,7 @@ COMPAT_SYSCALL_DEFINE4(clock_nanosleep, clockid_t, which_clock, int, flags,
return -EINVAL;
if (flags & TIMER_ABSTIME)
rmtp = NULL;
+ current->restart_block.fn = do_no_restart_syscall;
current->restart_block.nanosleep.type = rmtp ? TT_COMPAT : TT_NONE;
current->restart_block.nanosleep.compat_rmtp = rmtp;
