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@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230105134403.754986-1-jannh@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 23af5eca11b14c81eaba6e5c49f791806f110c2e..97409581e9dacd1441d51c2827cbdfa34f905285 100644 (file)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -2126,6 +2126,7 @@ SYSCALL_DEFINE2(nanosleep, struct __kernel_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(timespec64_to_ktime(tu), HRTIMER_MODE_REL,
@@ -2147,6 +2148,7 @@ SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __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(timespec64_to_ktime(tu), HRTIMER_MODE_REL,

diff --git a/kernel/time/posix-stubs.c b/kernel/time/posix-stubs.c
index fcb3b21d8bdcd444f32165f98dd9fe078b3d2446..3783d07d60ba038736e6566eecc9d72b00fe6487 100644 (file)
--- a/kernel/time/posix-stubs.c
+++ b/kernel/time/posix-stubs.c
@@ -146,6 +146,7 @@ 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;
        texp = timespec64_to_ktime(t);
@@ -239,6 +240,7 @@ SYSCALL_DEFINE4(clock_nanosleep_time32, 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;
        texp = timespec64_to_ktime(t);

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 5dead89308b7424e0c5a718d6c9943ac141c23cc..0c8a87a11b39df91a8aa297d3852d957e98a37ac 100644 (file)
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -1270,6 +1270,7 @@ 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;
 
@@ -1297,6 +1298,7 @@ SYSCALL_DEFINE4(clock_nanosleep_time32, 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;