From 43b1bee5de7ae4fb9d2329754bb02c7dfc7a56ad Mon Sep 17 00:00:00 2001 From: Mehul Rao Date: Thu, 5 Mar 2026 14:31:46 -0500 Subject: [PATCH] ublk: fix NULL pointer dereference in ublk_ctrl_set_size() 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 004f367243b6..41ed30a18b37 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 ublksrv_ctrl_cmd *header) return 0; } -static void ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksrv_ctrl_cmd *header) +static int ublk_ctrl_set_size(struct ublk_device *ub, const struct ublksrv_ctrl_cmd *header) { struct ublk_param_basic *p = &ub->params.basic; u64 new_size = header->data[0]; + int ret = 0; mutex_lock(&ub->mutex); + if (!ub->ub_disk) { + ret = -ENODEV; + goto out; + } p->dev_sectors = new_size; set_capacity_and_notify(ub->ub_disk, p->dev_sectors); +out: mutex_unlock(&ub->mutex); + return ret; } struct count_busy { @@ -5335,8 +5342,7 @@ static int ublk_ctrl_uring_cmd(struct io_uring_cmd *cmd, ret = ublk_ctrl_end_recovery(ub, &header); break; case UBLK_CMD_UPDATE_SIZE: - ublk_ctrl_set_size(ub, &header); - ret = 0; + ret = ublk_ctrl_set_size(ub, &header); break; case UBLK_CMD_QUIESCE_DEV: ret = ublk_ctrl_quiesce_dev(ub, &header);