[PATCH] fs/select: reject negative timeval components in do_compat_select()

[Avi Weiss]

do_compat_select() normalizes old_timeval32 before validating the
timeout. Negative seconds and microseconds can cancel each other,
causing compat select() and old_select() to accept invalid timeouts.

Reject negative components before normalization (as kern_select()
already does) - and preserve the handling of oversized positive
tv_usec values.

A 32-bit syscall reproducer confirmed four incorrect results on the
unpatched kernel. With the fix applied, all my test cases passed on
both compat select interfaces.

Fixes: 4d36a9e65d49 ("select: deal with math overflow from borderline valid userland data")
Signed-off-by: Avi Weiss <thnkslprpt@xxxxxxxxx>
---
 fs/select.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/select.c b/fs/select.c
index 95d76531015aa..8b6d1dd2977c6 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -1265,6 +1265,8 @@ static int do_compat_select(int n, compat_ulong_t __user *inp,
 		if (copy_from_user(&tv, tvp, sizeof(tv)))
 			return -EFAULT;
 
+		if (tv.tv_sec < 0 || tv.tv_usec < 0)
+			return -EINVAL;
 		to = &end_time;
 		if (poll_select_set_timeout(to,
 				tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),

base-commit: 36aad21d50d1af3f6954bb0c988257a908202477
-- 
2.43.0