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Thu, 05 Mar 2026 11:32:30 -0800 (PST) Received: from desktop-linux.python-stargazer.ts.net ([50.168.180.218]) by smtp.gmail.com with ESMTPSA id 00721157ae682-79876a9004dsm92357617b3.6.2026.03.05.11.32.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Mar 2026 11:32:30 -0800 (PST) From: Mehul Rao To: ming.lei@redhat.com, axboe@kernel.dk Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Mehul Rao Subject: [PATCH] ublk: fix NULL pointer dereference in ublk_ctrl_set_size() Date: Thu, 5 Mar 2026 14:31:46 -0500 Message-ID: <20260305193146.304526-1-mehulrao@gmail.com> X-Mailer: git-send-email 2.53.0 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" ublk_ctrl_set_size() unconditionally dereferences ub->ub_disk via set_capacity_and_notify() without checking if it is NULL. ub->ub_disk is NULL before UBLK_CMD_START_DEV completes (it is only assigned in ublk_ctrl_start_dev()) and after UBLK_CMD_STOP_DEV runs (ublk_detach_disk() sets it to NULL). Since the UBLK_CMD_UPDATE_SIZE handler performs no state validation, a user can trigger a NULL pointer dereference by sending UPDATE_SIZE to a device that has been added but not yet started, or one that has been stopped. Fix this by checking ub->ub_disk under ub->mutex before dereferencing it, and returning -ENODEV if the disk is not available. Fixes: 98b995660bff ("ublk: Add UBLK_U_CMD_UPDATE_SIZE") Cc: stable@vger.kernel.org Signed-off-by: Mehul Rao Reviewed-by: Ming Lei --- drivers/block/ublk_drv.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 004f36724..41ed30a18 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -5006,15 +5006,22 @@ static int ublk_ctrl_get_features(const struct ublk= srv_ctrl_cmd *header) return 0; } =20 -static void ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksr= v_ctrl_cmd *header) +static int ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksrv= _ctrl_cmd *header) { struct ublk_param_basic *p =3D &ub->params.basic; u64 new_size =3D header->data[0]; + int ret =3D 0; =20 mutex_lock(&ub->mutex); + if (!ub->ub_disk) { + ret =3D -ENODEV; + goto out; + } p->dev_sectors =3D new_size; set_capacity_and_notify(ub->ub_disk, p->dev_sectors); +out: mutex_unlock(&ub->mutex); + return ret; } =20 struct count_busy { @@ -5335,8 +5342,7 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *c= md, ret =3D ublk_ctrl_end_recovery(ub, &header); break; case UBLK_CMD_UPDATE_SIZE: - ublk_ctrl_set_size(ub, &header); - ret =3D 0; + ret =3D ublk_ctrl_set_size(ub, &header); break; case UBLK_CMD_QUIESCE_DEV: ret =3D ublk_ctrl_quiesce_dev(ub, &header); --=20 2.53.0