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([2405:201:682f:389d:eaca:4d1a:b10a:82a7]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29bce40acbbsm93540005ad.11.2025.11.30.01.27.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Nov 2025 01:27:38 -0800 (PST) From: Deepanshu Kartikey To: brauner@kernel.org, viro@zeniv.linux.org.uk, neil@brown.name, amir73il@gmail.com, jlayton@kernel.org Cc: linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+b74150fd2ef40e716ca2@syzkaller.appspot.com Subject: [PATCH] ipc/mqueue: fix dentry refcount imbalance in prepare_open() Date: Sun, 30 Nov 2025 14:57:31 +0530 Message-ID: <20251130092731.726288-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" When opening an existing message queue, prepare_open() does not increment the dentry refcount, but end_creating() always calls dput(). This causes a refcount imbalance that triggers a WARN_ON_ONCE in fast_dput() when the file is later closed. The creation path via vfs_mkobj() correctly increments the refcount, but the "already exists" path was missing the corresponding dget(). Add the missing dget() call when opening an existing queue to balance the dput() in end_creating(). Reported-by: syzbot+b74150fd2ef40e716ca2@syzkaller.appspot.com Closes: https://syzkaller.appspot.com/bug?extid=3Db74150fd2ef40e716ca2 Signed-off-by: Deepanshu Kartikey --- ipc/mqueue.c | 1 + 1 file changed, 1 insertion(+) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 328bcc3ee3ad..63ff2c322549 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -883,6 +883,7 @@ static int prepare_open(struct dentry *dentry, int ofla= g, int ro, if ((oflag & O_ACCMODE) =3D=3D (O_RDWR | O_WRONLY)) return -EINVAL; acc =3D oflag2acc[oflag & O_ACCMODE]; + dget(dentry); return inode_permission(&nop_mnt_idmap, d_inode(dentry), acc); } =20 --=20 2.43.0