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authorOleg Nesterov <oleg@redhat.com>2017-09-01 18:55:33 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2017-09-01 22:07:35 +0200
commit138e4ad67afd5c6c318b056b4d17c17f2c0ca5c0 (patch)
tree2d214e233ed80eb887d8a81e11be2613c37d9874 /net/kcm
parentMerge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net (diff)
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epoll: fix race between ep_poll_callback(POLLFREE) and ep_free()/ep_remove()
The race was introduced by me in commit 971316f0503a ("epoll: ep_unregister_pollwait() can use the freed pwq->whead"). I did not realize that nothing can protect eventpoll after ep_poll_callback() sets ->whead = NULL, only whead->lock can save us from the race with ep_free() or ep_remove(). Move ->whead = NULL to the end of ep_poll_callback() and add the necessary barriers. TODO: cleanup the ewake/EPOLLEXCLUSIVE logic, it was confusing even before this patch. Hopefully this explains use-after-free reported by syzcaller: BUG: KASAN: use-after-free in debug_spin_lock_before ... _raw_spin_lock_irqsave+0x4a/0x60 kernel/locking/spinlock.c:159 ep_poll_callback+0x29f/0xff0 fs/eventpoll.c:1148 this is spin_lock(eventpoll->lock), ... Freed by task 17774: ... kfree+0xe8/0x2c0 mm/slub.c:3883 ep_free+0x22c/0x2a0 fs/eventpoll.c:865 Fixes: 971316f0503a ("epoll: ep_unregister_pollwait() can use the freed pwq->whead") Reported-by: 范龙飞 <long7573@126.com> Cc: stable@vger.kernel.org Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'net/kcm')
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