[PATCH] fuse: wait for sync init request after abort

[David Lee <david.lee@trailofbits.com>]

After a fatal signal interrupts synchronous FUSE_INIT,
request_wait_answer() aborts the channel and returns immediately.  If the
request is in an FR_LOCKED reply-copy interval, fuse_chan_abort() leaves
it for the writer to finish.  The synchronous caller can then free the
fuse_init_args that owns the reply destination while the writer is still
copying into it.

Wait for fuse_request_end() after aborting the channel.  This keeps the
synchronous caller's reply storage alive until any locked copy has
finished, while preserving the fatal-signal abort behavior.

Fixes: 204aa22a686b ("fuse: abort on fatal signal during sync init")
Cc: stable@vger.kernel.org
Bug found and triaged by OpenAI Security Research and 
validated by Trail of Bits.

Assisted-by: Codex:gpt-5.6-sol gpt-5.5-cyber
Signed-off-by: Kyle Zeng <kylebot@openai.com>
---
Trail of Bits has a reproducer for this bug that triggers a
KASAN use-after-free and can share if needed.

 fs/fuse/dev.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 5763a7cd3..deee1585d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -725,6 +725,8 @@ static void request_wait_answer(struct fuse_req *req)
 
 		if (req->args->abort_on_kill) {
 			fuse_chan_abort(fch, false);
+			wait_event(req->waitq,
+				   test_bit(FR_FINISHED, &req->flags));
 			return;
 		}
 
-- 
2.53.0