[PATCH 1/2] pipe: fix potential use-after-free in pipe_read()

[Zhen Lei <thunder.leizhen@xxxxxxxxxx>]

Accessing buf->flags after pipe_buf_release(pipe, buf) is unsafe, because
the 'buf' memory maybe freed.

Fixes: e7d553d69cf6 ("pipe: Add notification lossage handling")
Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
---
 fs/pipe.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 6d4342bad9f15b2..302f1e50ce3be1d 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -319,10 +319,12 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 			}
 
 			if (!buf->len) {
+				unsigned int __maybe_unused flags = buf->flags;
+
 				pipe_buf_release(pipe, buf);
 				spin_lock_irq(&pipe->rd_wait.lock);
 #ifdef CONFIG_WATCH_QUEUE
-				if (buf->flags & PIPE_BUF_FLAG_LOSS)
+				if (flags & PIPE_BUF_FLAG_LOSS)
 					pipe->note_loss = true;
 #endif
 				tail++;
-- 
2.26.0.106.g9fadedd