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| author | Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn> | 2026-05-28 13:39:16 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2026-07-04 13:45:07 +0200 |
| commit | a7656d368265d085ac9bb85ab31b0cdb72ad8c38 (patch) | |
| tree | 6b62738157548526daa0cc28a2781102735761ba | |
| parent | 99c21e7263248c3f084756bfae08163cc5d6c62f (diff) | |
| download | linux-a7656d368265d085ac9bb85ab31b0cdb72ad8c38.tar.gz linux-a7656d368265d085ac9bb85ab31b0cdb72ad8c38.zip | |
9p: avoid putting oldfid in p9_client_walk() error path
commit 1a3860d46e3eb47dbd60339783cdad7904486b9f upstream.
When p9_client_walk() is called with clone set to false, fid aliases
oldfid. If the walk subsequently fails after the request has been sent,
the error path jumps to clunk_fid, which currently calls p9_fid_put(fid)
unconditionally.
This drops a reference to oldfid even though ownership of oldfid remains
with the caller. If this is the last reference, oldfid can be clunked and
destroyed while the caller still expects it to be valid. A later use or
put of oldfid can then trigger a use-after-free or refcount underflow.
Fix this by only putting fid in the clunk_fid error path when it does not
alias oldfid, matching the existing guard in the error path below.
This can be triggered when a multi-component walk is split into multiple
p9_client_walk() calls and a later non-cloning walk fails. A reproducer
and refcount warning logs are available on request.
Fixes: b48dbb998d70 ("9p fid refcount: add p9_fid_get/put wrappers")
Cc: stable@vger.kernel.org
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM 5.1
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Message-ID: <20260528053918.53550-1-zhaoyz24@mails.tsinghua.edu.cn>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | net/9p/client.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/net/9p/client.c b/net/9p/client.c index f0dcf252af7e..4b942d02c29c 100644 --- a/net/9p/client.c +++ b/net/9p/client.c @@ -1092,7 +1092,8 @@ struct p9_fid *p9_client_walk(struct p9_fid *oldfid, uint16_t nwname, clunk_fid: kfree(wqids); - p9_fid_put(fid); + if (fid != oldfid) + p9_fid_put(fid); fid = NULL; error: |