Commit f5cb779ba163 ("ANDROID: binder: remove waitqueue when thread
exits.") fixed the use-after-free in eventpoll but aio still has the
same issue because it doesn't honor the POLLFREE flag.
Add support for the POLLFREE flag to force complete iocb inline in
aio_poll_wake(). A thread may use it to signal it's exit and/or request
to cleanup while pending poll request. In this case, aio_poll_wake()
needs to make sure it doesn't keep any reference to the queue entry
before returning from wake to avoid possible use after free via
poll_cancel() path.
The POLLFREE flag is no more exclusive to the epoll and is being
shared with the aio. Remove comment from poll.h to avoid confusion.
This fixes a use after free issue between binder thread and aio
interactions in certain sequence of events [1].
[1] https://lore.kernel.org/all/CAKUd0B_TCXRY4h1hTztfwWbNSFQqsudDLn2S_28csgWZmZAG3Q@xxxxxxxxxxxxxx/
Signed-off-by: Ramji Jiyani <ramjiyani@xxxxxxxxxx>
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
---
Changes since v1:
- Removed parenthesis around POLLFREE macro definition as per review.
- Updated description to refer UAF issue discussion this patch fixes.
- Updated description to remove reference to parenthesis change.
- Added Reviewed-by
---
fs/aio.c | 45 ++++++++++++++++++---------------
include/uapi/asm-generic/poll.h | 2 +-
2 files changed, 26 insertions(+), 21 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 51b08ab01dff..5d539c05df42 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1674,6 +1674,7 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
{
struct poll_iocb *req = container_of(wait, struct poll_iocb, wait);
struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, poll);
+ struct kioctx *ctx = iocb->ki_ctx;
__poll_t mask = key_to_poll(key);
unsigned long flags;
@@ -1683,29 +1684,33 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
list_del_init(&req->wait.entry);
- if (mask && spin_trylock_irqsave(&iocb->ki_ctx->ctx_lock, flags)) {
- struct kioctx *ctx = iocb->ki_ctx;
+ /*
+ * Use irqsave/irqrestore because not all filesystems (e.g. fuse)
+ * call this function with IRQs disabled and because IRQs have to
+ * be disabled before ctx_lock is obtained.
+ */
+ if (mask & POLLFREE) {
+ /* Force complete iocb inline to remove refs to deleted entry */
+ spin_lock_irqsave(&ctx->ctx_lock, flags);
+ } else if (!(mask && spin_trylock_irqsave(&ctx->ctx_lock, flags))) {
+ /* Can't complete iocb inline; schedule for later */
+ schedule_work(&req->work);
+ return 1;
+ }
- /*
- * Try to complete the iocb inline if we can. Use
- * irqsave/irqrestore because not all filesystems (e.g. fuse)
- * call this function with IRQs disabled and because IRQs
- * have to be disabled before ctx_lock is obtained.
- */
- list_del(&iocb->ki_list);
- iocb->ki_res.res = mangle_poll(mask);
- req->done = true;
- if (iocb->ki_eventfd && eventfd_signal_allowed()) {
- iocb = NULL;
- INIT_WORK(&req->work, aio_poll_put_work);
- schedule_work(&req->work);
- }
- spin_unlock_irqrestore(&ctx->ctx_lock, flags);
- if (iocb)
- iocb_put(iocb);
- } else {
+ /* complete iocb inline */
+ list_del(&iocb->ki_list);
+ iocb->ki_res.res = mangle_poll(mask);
+ req->done = true;
+ if (iocb->ki_eventfd && eventfd_signal_allowed()) {
+ iocb = NULL;
+ INIT_WORK(&req->work, aio_poll_put_work);
schedule_work(&req->work);
}
+ spin_unlock_irqrestore(&ctx->ctx_lock, flags);
+ if (iocb)
+ iocb_put(iocb);
+
return 1;
}
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
--
2.33.0.800.g4c38ced690-goog
