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fs/exec.c: work around icc miscompilation

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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 362e6663ef
("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 <[email protected]>
Cc: Jason Baron <[email protected]>
Cc: Al Viro <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Xi Wang 2013-01-11 14:31:48 -08:00 • committed by Linus Torvalds
commit 6d92d4f6a7
1 changed files with 2 additions and 1 deletions
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3
fs/exec.c
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@ -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;