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futex-prevent-requeue-pi-on-same-futex.patch futex: Forbid uaddr == uaddr2 in futex_requeue(..., requeue_pi=1)
If uaddr == uaddr2, then we have broken the rule of only requeueing from a non-pi futex to a pi futex with this call. If we attempt this, then dangling pointers may be left for rt_waiter resulting in an exploitable condition. This change brings futex_requeue() in line with futex_wait_requeue_pi() which performs the same check as per commit 6f7b0a2 ("futex: Forbid uaddr == uaddr2 in futex_wait_requeue_pi()") [ tglx: Compare the resulting keys as well, as uaddrs might be different depending on the mapping ] Fixes CVE-2014-3153. Reported-by: Pinkie Pie Signed-off-by: Will Drewry <wad@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Cc: stable@vger.kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Darren Hart <dvhart@linux.intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Diff for: kernel/futex.c

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Original file line numberDiff line numberDiff line change
@@ -1441,6 +1441,13 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
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struct futex_q *this, *next;
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if (requeue_pi) {
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/*
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* Requeue PI only works on two distinct uaddrs. This
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* check is only valid for private futexes. See below.
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*/
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if (uaddr1 == uaddr2)
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return -EINVAL;
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/*
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* requeue_pi requires a pi_state, try to allocate it now
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* without any locks in case it fails.
@@ -1479,6 +1486,15 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
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if (unlikely(ret != 0))
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goto out_put_key1;
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/*
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* The check above which compares uaddrs is not sufficient for
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* shared futexes. We need to compare the keys:
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*/
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if (requeue_pi && match_futex(&key1, &key2)) {
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ret = -EINVAL;
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goto out_put_keys;
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}
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hb1 = hash_futex(&key1);
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hb2 = hash_futex(&key2);
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@@ -2525,6 +2541,15 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
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if (ret)
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goto out_key2;
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/*
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* The check above which compares uaddrs is not sufficient for
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* shared futexes. We need to compare the keys:
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*/
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if (match_futex(&q.key, &key2)) {
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ret = -EINVAL;
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goto out_put_keys;
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}
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/* Queue the futex_q, drop the hb lock, wait for wakeup. */
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futex_wait_queue_me(hb, &q, to);
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