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Tue, 05 May 2026 02:52:11 -0700 (PDT) Received: from vini ([2401:4900:8fc8:907b:6dbd:bd6e:9d0b:e8cf]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-83965d38ab5sm2125855b3a.26.2026.05.05.02.52.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 May 2026 02:52:11 -0700 (PDT) From: Vineet Agarwal To: viro@zeniv.linux.org.uk Cc: brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Vineet Agarwal , syzbot Subject: [PATCH] fs/namespace: fix NULL pointer dereference in do_lock_mount() Date: Tue, 5 May 2026 15:21:31 +0530 Message-ID: <20260505095156.178351-1-agarwal.vineet2006@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Syzkaller reported a NULL pointer dereference in do_lock_mount() when calling inode_lock() on a dentry without an associated inode. where_to_mount() may return a negative dentry (without an inode) due to concurrent unlink or mount changes. The current code does not validate this before calling inode_lock(), leading to a crash. Fix this by checking dentry and dentry->d_inode before acquiring the inode lock. Reported-by: syzbot Closes: https://syzkaller.appspot.com/ Signed-off-by: Vineet Agarwal --- fs/namespace.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index fe919abd2f01..b1dccdf06836 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2760,6 +2760,17 @@ static void do_lock_mount(const struct path *path, } } + if (unlikely(!dentry || !dentry->d_inode)) { + err = -ENOENT; + if (&m->mnt != path->mnt) { + if (dentry) + dput(dentry); + mntput(&m->mnt); + } + res->parent = ERR_PTR(err); + return; + } + inode_lock(dentry->d_inode); namespace_lock(); -- 2.54.0