[SCSI] st: fix race in st_scsi_execute_end

The call to complete() in st_scsi_execute_end() wakes up sleeping thread
in write_behind_check(), which frees the st_request, thus invalidating
the pointer to the associated bio structure, which is then passed to the
blk_rq_unmap_user(). Fix by storing pointer to bio structure into
temporary local variable.

This bug is present since at least linux-2.6.32.

CC: stable@kernel.org
Signed-off-by: Petr Uzel <petr.uzel@suse.cz>
Reported-by: Juergen Groß <juergen.gross@ts.fujitsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 1871b8ae83ae..9b28f39bac26 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -462,14 +462,16 @@ static void st_scsi_execute_end(struct request *req, int uptodate)
 {
         struct st_request *SRpnt = req->end_io_data;
         struct scsi_tape *STp = SRpnt->stp;
+        struct bio *tmp;
 
         STp->buffer->cmdstat.midlevel_result = SRpnt->result = req->errors;
         STp->buffer->cmdstat.residual = req->resid_len;
 
+        tmp = SRpnt->bio;
         if (SRpnt->waiting)
                 complete(SRpnt->waiting);
 
-        blk_rq_unmap_user(SRpnt->bio);
+        blk_rq_unmap_user(tmp);
         __blk_put_request(req->q, req);
 }