[213/264] [SCSI] st: fix race in st_scsi_execute_end

[Greg KH]

3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Petr Uzel <petr.uzel@xxxxxxx>

commit c68bf8eeaa57c852e74adcf597237be149eef830 upstream.

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.

Signed-off-by: Petr Uzel <petr.uzel@xxxxxxx>
Reported-by: Juergen GroÃ? <juergen.gross@xxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Acked-by: Kai Mäkisara <kai.makisara@xxxxxxxxxxx>
Signed-off-by: James Bottomley <JBottomley@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/scsi/st.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -462,14 +462,16 @@ static void st_scsi_execute_end(struct r
 {
 	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);
 }
 


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