Avoid that scsi_show_rq() triggers a NULL pointer dereference if
called after sd_uninit_command(). Swap the NULL pointer assignment
and the mempool_free() call in sd_uninit_command() to make it less
likely that scsi_show_rq() triggers a use-after-free. Note: even
with these changes scsi_show_rq() can trigger a use-after-free but
that's a lesser evil than e.g. suppressing debug information for
T10-PI commands completely. This patch fixes the following oops:
BUG: unable to handle kernel NULL pointer dereference at (null)
IP: scsi_format_opcode_name+0x1a/0x1c0
CPU: 1 PID: 1881 Comm: cat Not tainted 4.14.0-rc2.blk_mq_io_hang+ #516
Call Trace:
__scsi_format_command+0x27/0xc0
scsi_show_rq+0x5c/0xc0
__blk_mq_debugfs_rq_show+0x116/0x130
blk_mq_debugfs_rq_show+0xe/0x10
seq_read+0xfe/0x3b0
full_proxy_read+0x54/0x90
__vfs_read+0x37/0x160
vfs_read+0x96/0x130
SyS_read+0x55/0xc0
entry_SYSCALL_64_fastpath+0x1a/0xa5
Fixes: 0eebd005dd07 ("scsi: Implement blk_mq_ops.show_rq()")
Reported-by: Ming Lei <ming.lei@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxxxx>
Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/scsi/scsi_debugfs.c | 6 ++++--
drivers/scsi/sd.c | 4 +++-
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/scsi_debugfs.c b/drivers/scsi/scsi_debugfs.c
index 01f08c03f2c1..c3765d29fd3f 100644
--- a/drivers/scsi/scsi_debugfs.c
+++ b/drivers/scsi/scsi_debugfs.c
@@ -8,9 +8,11 @@ void scsi_show_rq(struct seq_file *m, struct request *rq)
{
struct scsi_cmnd *cmd = container_of(scsi_req(rq), typeof(*cmd), req);
int msecs = jiffies_to_msecs(jiffies - cmd->jiffies_at_alloc);
- char buf[80];
+ const u8 *const cdb = READ_ONCE(cmd->cmnd);
+ char buf[80] = "(?)";
- __scsi_format_command(buf, sizeof(buf), cmd->cmnd, cmd->cmd_len);
+ if (cdb)
+ __scsi_format_command(buf, sizeof(buf), cdb, cmd->cmd_len);
seq_printf(m, ", .cmd=%s, .retries=%d, allocated %d.%03d s ago", buf,
cmd->retries, msecs / 1000, msecs % 1000);
}
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index d175c5c5ccf8..d841743b2107 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1284,6 +1284,7 @@ static int sd_init_command(struct scsi_cmnd *cmd)
static void sd_uninit_command(struct scsi_cmnd *SCpnt)
{
struct request *rq = SCpnt->request;
+ u8 *cmnd;
if (SCpnt->flags & SCMD_ZONE_WRITE_LOCK)
sd_zbc_write_unlock_zone(SCpnt);
@@ -1292,9 +1293,10 @@ static void sd_uninit_command(struct scsi_cmnd *SCpnt)
__free_page(rq->special_vec.bv_page);
if (SCpnt->cmnd != scsi_req(rq)->cmd) {
- mempool_free(SCpnt->cmnd, sd_cdb_pool);
+ cmnd = SCpnt->cmnd;
SCpnt->cmnd = NULL;
SCpnt->cmd_len = 0;
+ mempool_free(cmnd, sd_cdb_pool);
}
}
--
2.15.0
