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From:   Zhen Lei <thunder.leizhen@huawei.com>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>,
        <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>
CC:     Zhen Lei <thunder.leizhen@huawei.com>,
        David Howells <dhowells@redhat.com>
Subject: [PATCH] pipe: fix potential use-after-free in pipe_read()
Date:   Thu, 17 Nov 2022 19:53:23 +0800
Message-ID: <20221117115323.1718-1-thunder.leizhen@huawei.com>
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Precedence: bulk

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

In fact, pipe->note_loss does not need the protection of spinlock
pipe->rd_wait.lock, it only needs the protection of __pipe_lock(pipe). So
make the assignment of pipe->note_loss complete before releasing 'buf' to
eliminate the risk.

Fixes: e7d553d69cf6 ("pipe: Add notification lossage handling")
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
---
 fs/pipe.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 42c7ff41c2dba29..0f873949337ed28 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -321,12 +321,12 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
 			}
 
 			if (!buf->len) {
-				pipe_buf_release(pipe, buf);
-				spin_lock_irq(&pipe->rd_wait.lock);
 #ifdef CONFIG_WATCH_QUEUE
 				if (buf->flags & PIPE_BUF_FLAG_LOSS)
 					pipe->note_loss = true;
 #endif
+				pipe_buf_release(pipe, buf);
+				spin_lock_irq(&pipe->rd_wait.lock);
 				tail++;
 				pipe->tail = tail;
 				spin_unlock_irq(&pipe->rd_wait.lock);
-- 
2.25.1