path: root/kernel/futex.c
diff options
authorThomas Gleixner <tglx@linutronix.de>2011-03-14 10:34:35 +0100
committerThomas Gleixner <tglx@linutronix.de>2011-03-14 21:08:47 +0100
commit6e0aa9f8a8190e0879a29bd67aa606b51734a122 (patch)
tree66b92176051147b87031cc2755639c39f8a900f8 /kernel/futex.c
parent995612178c88407d8330f580ba6572cb8b284dd8 (diff)
futex: Deobfuscate handle_futex_death()
handle_futex_death() uses futex_atomic_cmpxchg_inatomic() without disabling page faults. That's ok, but totally non obvious. We don't hold locks so we actually can and want to fault here, because the get_user() before futex_atomic_cmpxchg_inatomic() does not guarantee a R/W mapping. We could just add a big fat comment to explain this, but actually changing the code so that the functionality is entirely clear is better. Use the helper function which disables page faults around the futex_atomic_cmpxchg_inatomic() and handle a fault with a call to fault_in_user_writeable() as all other places in the futex code do as well. Pointed-out-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Darren Hart <darren@dvhart.com> Cc: Michel Lespinasse <walken@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Matt Turner <mattst88@gmail.com> Cc: Russell King <linux@arm.linux.org.uk> Cc: David Howells <dhowells@redhat.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Michal Simek <monstr@monstr.eu> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: "James E.J. Bottomley" <jejb@parisc-linux.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: "David S. Miller" <davem@davemloft.net> Cc: Chris Metcalf <cmetcalf@tilera.com> LKML-Reference: <alpine.LFD.2.00.1103141126590.2787@localhost6.localdomain6> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/futex.c')
1 files changed, 14 insertions, 3 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index c6bef6e404f..e9251d934f7 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2458,9 +2458,20 @@ retry:
* userspace.
- if (futex_atomic_cmpxchg_inatomic(&nval, uaddr, uval, mval))
- return -1;
+ /*
+ * We are not holding a lock here, but we want to have
+ * the pagefault_disable/enable() protection because
+ * we want to handle the fault gracefully. If the
+ * access fails we try to fault in the futex with R/W
+ * verification via get_user_pages. get_user() above
+ * does not guarantee R/W access. If that fails we
+ * give up and leave the futex locked.
+ */
+ if (cmpxchg_futex_value_locked(&nval, uaddr, uval, mval)) {
+ if (fault_in_user_writeable(uaddr))
+ return -1;
+ goto retry;
+ }
if (nval != uval)
goto retry;