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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e6c6dd585sm5925296a91.0.2026.09.19.15.17.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 15:17:34 -0700 (PDT) From: Hui Peng To: ericvh@kernel.org, lucho@ionkov.net, asmadeus@codewreck.org, linux_oss@crudebyte.com Cc: v9fs@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH] 9p: reject RERROR/RLERROR with zero errcode and guard 0-link drop_nlink() Date: Sat, 19 Sep 2026 22:17:34 +0000 Message-ID: <20260919221734.3708000-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: v9fs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Fix two issues in 9p client and VFS inode handling: 1. In p9_check_errors() (net/9p/client.c), a malicious or buggy 9p server returning P9_RERROR or P9_RLERROR with ecode == 0 causes p9_check_errors() to return 0 (success) while leaving the unparsed response payload as if the expected reply message type succeeded. Map ecode == 0 on RERROR / RLERROR to -EPROTO. 2. In v9fs_dec_count() (fs/9p/vfs_inode.c), only call drop_nlink() when inode->i_nlink > 0 so unlinking an inode whose server-reported nlink was already 0 does not underflow i_nlink and trigger WARN_ON(inode->i_nlink == 0). Fixes: bd238fb431f3 ("9p: Reorganization of 9p file system code") Assisted-by: LLM Signed-off-by: Hui Peng --- diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c index 3829554ca369..12db5ff61554 100644 --- a/fs/9p/vfs_inode.c +++ b/fs/9p/vfs_inode.c @@ -503,7 +503,7 @@ static void v9fs_dec_count(struct inode *inode) if (!(v9ses->cache & (CACHE_META | CACHE_LOOSE))) return; - if (!S_ISDIR(inode->i_mode) || inode->i_nlink > 2) + if (S_ISDIR(inode->i_mode) ? inode->i_nlink > 2 : inode->i_nlink > 0) drop_nlink(inode); } diff --git a/net/9p/client.c b/net/9p/client.c index ef64546c6d52..e63e8c2a853d 100644 --- a/net/9p/client.c +++ b/net/9p/client.c @@ -448,6 +448,9 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req) p9_debug(P9_DEBUG_9P, "<<< RLERROR (%d)\n", -ecode); } + if (!err) + err = -EPROTO; + return err; out_err: