fs/exec.c: work around icc miscompilation

xiw · torvalds · commit 6d92d4f6a747 · 2013-01-11T14:54:55.000-08:00
The tricky problem is this check: if (i++ >= max) icc (mis)optimizes this check as: if (++i > max) The check now becomes a no-op since max is MAX_ARG_STRINGS (0x7FFFFFFF). This is "allowed" by the C standard, assuming i++ never overflows, because signed integer overflow is undefined behavior. This optimization effectively reverts the previous commit 362e666 ("exec.c, compat.c: fix count(), compat_count() bounds checking") that tries to fix the check. This patch simply moves ++ after the check. Signed-off-by: Xi Wang <xi.wang@gmail.com> Cc: Jason Baron <jbaron@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/exec.c b/fs/exec.c
@@ -434,8 +434,9 @@ static int count(struct user_arg_ptr argv, int max)
 			if (IS_ERR(p))
 				return -EFAULT;
 
-			if (i++ >= max)
+			if (i >= max)
 				return -E2BIG;
+			++i;
 
 			if (fatal_signal_pending(current))
 				return -ERESTARTNOHAND;
