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([2401:4900:30d2:c11f:7948:960a:6d92:5986]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13e53094d65sm1378443c88.13.2026.07.24.18.44.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Jul 2026 18:44:56 -0700 (PDT) From: Deepanshu Kartikey To: ericvh@kernel.org, lucho@ionkov.net, asmadeus@codewreck.org, linux_oss@crudebyte.com Cc: v9fs@lists.linux.dev, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+344c09c64fcd8d3d2782@syzkaller.appspotmail.com Subject: [PATCH] 9p: don't WARN_ONCE on racy symlink fid lookup failure Date: Sat, 25 Jul 2026 07:14:48 +0530 Message-ID: <20260725014448.18711-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: v9fs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit v9fs_init_request() WARN_ONCE()s when v9fs_fid_lookup() fails for a symlink read via the page cache. This is a benign TOCTOU race: a concurrent unlink()/rename() can remove the target between the walk finding the dentry and p9_client_walk() completing, so the lookup legitimately fails with -ENOENT (observed: dentry=/file0, err=-2). With panic_on_warn=1, this WARN escalates to a full kernel panic -- an unprivileged local DoS reachable by racing mount() against a concurrent unlink/rename. Return the error directly instead of WARN_ONCE(). Reported-by: syzbot+344c09c64fcd8d3d2782@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=344c09c64fcd8d3d2782 Signed-off-by: Deepanshu Kartikey --- fs/9p/vfs_addr.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c index 1ac0b3dcc077..121679488ab9 100644 --- a/fs/9p/vfs_addr.c +++ b/fs/9p/vfs_addr.c @@ -140,13 +140,16 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file) goto no_fid; p9_fid_get(fid); } else if (S_ISLNK(rreq->inode->i_mode)) { + /* racing unlink/rename can make this fail with -ENOENT; + * that's expected, not a kernel bug, so don't WARN + */ dentry = d_find_any_alias(rreq->inode); if (!dentry) goto no_fid; fid = v9fs_fid_lookup(dentry); dput(dentry); if (IS_ERR(fid)) - goto no_fid; + return PTR_ERR(fid); } else { fid = v9fs_fid_find_inode(rreq->inode, writing, INVALID_UID, true); if (!fid) -- 2.43.0