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authorEric Biggers <ebiggers@google.com>2021-12-09 04:04:55 +0300
committerEric Biggers <ebiggers@google.com>2021-12-09 21:49:56 +0300
commit50252e4b5e989ce64555c7aef7516bdefc2fea72 (patch)
tree56359965f0f6d072dd9141ddce3fea3c8b22fd7e /include
parent363bee27e25804d8981dd1c025b4ad49dc39c530 (diff)
downloadlinux-50252e4b5e989ce64555c7aef7516bdefc2fea72.tar.xz
aio: fix use-after-free due to missing POLLFREE handling
signalfd_poll() and binder_poll() are special in that they use a waitqueue whose lifetime is the current task, rather than the struct file as is normally the case. This is okay for blocking polls, since a blocking poll occurs within one task; however, non-blocking polls require another solution. This solution is for the queue to be cleared before it is freed, by sending a POLLFREE notification to all waiters. Unfortunately, only eventpoll handles POLLFREE. A second type of non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't handle POLLFREE. This allows a use-after-free to occur if a signalfd or binder fd is polled with aio poll, and the waitqueue gets freed. Fix this by making aio poll handle POLLFREE. A patch by Ramji Jiyani <ramjiyani@google.com> (https://lore.kernel.org/r/20211027011834.2497484-1-ramjiyani@google.com) tried to do this by making aio_poll_wake() always complete the request inline if POLLFREE is seen. However, that solution had two bugs. First, it introduced a deadlock, as it unconditionally locked the aio context while holding the waitqueue lock, which inverts the normal locking order. Second, it didn't consider that POLLFREE notifications are missed while the request has been temporarily de-queued. The second problem was solved by my previous patch. This patch then properly fixes the use-after-free by handling POLLFREE in a deadlock-free way. It does this by taking advantage of the fact that freeing of the waitqueue is RCU-delayed, similar to what eventpoll does. Fixes: 2c14fa838cbe ("aio: implement IOCB_CMD_POLL") Cc: <stable@vger.kernel.org> # v4.18+ Link: https://lore.kernel.org/r/20211209010455.42744-6-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'include')
-rw-r--r--include/uapi/asm-generic/poll.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/uapi/asm-generic/poll.h b/include/uapi/asm-generic/poll.h
index 41b509f410bf..f9c520ce4bf4 100644
--- a/include/uapi/asm-generic/poll.h
+++ b/include/uapi/asm-generic/poll.h
@@ -29,7 +29,7 @@
#define POLLRDHUP 0x2000
#endif
-#define POLLFREE (__force __poll_t)0x4000 /* currently only for epoll */
+#define POLLFREE (__force __poll_t)0x4000
#define POLL_BUSY_LOOP (__force __poll_t)0x8000