linux-kernel - [PATCH] st: fix race in st_scsi_execute

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Date:	Fri, 21 Oct 2011 13:31:09 +0200
From:	Petr Uzel <petr.uzel@...e.cz>
To:	linux-kernel@...r.kernel.org, Willem Riede <osst@...de.org>
Cc:	jack@...e.cz, linux-scsi@...r.kernel.org,
	juergen.gross@...fujitsu.com
Subject: [PATCH] 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@...nel.org
Signed-off-by: Petr Uzel <petr.uzel@...e.cz>
Reported-by: Juergen Groß <juergen.gross@...fujitsu.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 drivers/scsi/st.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 1871b8a..9b28f39 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);
 }
 
-- 
1.7.3.4


Petr

--
Petr Uzel
IRC: ptr_uzl @ freenode

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