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Petersen (Oracle)" , Sasha Levin Subject: [PATCH 5.15 530/571] scsi: st: Fix use-after-free race between st_remove() and st_open() Date: Wed, 28 Oct 2026 18:01:17 +0100 Message-ID: <20261028170020.606598943@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170008.009143722@linuxfoundation.org> References: <20261028170008.009143722@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Laurence Oberman commit 71caf7f84bd62a4bf91cc95abd2de690afb8d15f upstream. st_remove() drops the probe reference on the scsi_tape with kref_put() and only afterwards removes its index from st_index_idr. If that was the last reference, scsi_tape_release() frees the structure while it is still published in the idr. scsi_tape_get(), called from st_open(), looks up the tape in st_index_idr and takes a reference under st_ref_mutex and st_index_lock. remove_cdevs() does not wait for opens that are already past chrdev_open(), so an open that is blocked on st_ref_mutex while st_remove() holds it can take the mutex as soon as st_remove() drops it, find the freed tpnt in the idr and call kref_get() on it: BUG: KASAN: slab-use-after-free in st_open Write of size 4 ... st_open (drivers/scsi/st.c:254 drivers/scsi/st.c:1291) chrdev_open ... Freed by task ...: kfree st_remove (drivers/scsi/st.c:4512) Remove the index from the idr before dropping the reference, all under st_ref_mutex. A concurrent scsi_tape_get() now either runs first and holds a valid reference that keeps the tape alive, or runs afterwards and finds nothing, so st_open() fails with -ENXIO. This restores the ordering st_remove() had before the conversion to st_index_idr, where the tape was unpublished from scsi_tapes[] before the final kref_put(). Fixes: 6c648d95a6af ("[SCSI] st: get rid of scsi_tapes array") Cc: stable@vger.kernel.org Reported-by: Dingisoul Closes: https://lore.kernel.org/linux-scsi/20261007211520.1428497-1-dingiso.kernel@gmail.com/ Tested-by: Dingisoul Signed-off-by: Laurence Oberman Link: https://patch.msgid.link/20261013202548.249628-1-loberman@redhat.com Signed-off-by: Martin K. Petersen (Oracle) [ loberman: st_remove() still returns int in 5.15; context adjusted ] Signed-off-by: Laurence Oberman Signed-off-by: Sasha Levin --- drivers/scsi/st.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c index 65b23015d1f23..2783419ef5f42 100644 --- a/drivers/scsi/st.c +++ b/drivers/scsi/st.c @@ -4439,11 +4439,11 @@ static int st_remove(struct device *dev) remove_cdevs(tpnt); mutex_lock(&st_ref_mutex); - kref_put(&tpnt->kref, scsi_tape_release); - mutex_unlock(&st_ref_mutex); spin_lock(&st_index_lock); idr_remove(&st_index_idr, index); spin_unlock(&st_index_lock); + kref_put(&tpnt->kref, scsi_tape_release); + mutex_unlock(&st_ref_mutex); return 0; } -- 2.53.0