lkml.org 
[lkml]   [2007]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[25/50] futex_compat: fix list traversal bugs

From: Arnd Bergmann <arnd@arndb.de>

commit 179c85ea53bef807621f335767e41e23f86f01df in mainline.

The futex list traversal on the compat side appears to have
a bug.

It's loop termination condition compares:

while (compat_ptr(uentry) != &head->list)

But that can't be right because "uentry" has the special
"pi" indicator bit still potentially set at bit 0. This
is cleared by fetch_robust_entry() into the "entry"
return value.

What this seems to mean is that the list won't terminate
when list iteration gets back to the the head. And we'll
also process the list head like a normal entry, which could
cause all kinds of problems.

So we should check for equality with "entry". That pointer
is of the non-compat type so we have to do a little casting
to keep the compiler and sparse happy.

The same problem can in theory occur with the 'pending'
variable, although that has not been reported from users
so far.

Based on the original patch from David Miller.

Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
kernel/futex_compat.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -61,10 +61,10 @@ void compat_exit_robust_list(struct task
if (fetch_robust_entry(&upending, &pending,
&head->list_op_pending, &pip))
return;
- if (upending)
+ if (pending)
handle_futex_death((void __user *)pending + futex_offset, curr, pip);

- while (compat_ptr(uentry) != &head->list) {
+ while (entry != (struct robust_list __user *) &head->list) {
/*
* A pending lock might already be on the list, so
* dont process it twice:
--
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-09-24 18:37    [W:0.136 / U:0.504 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site