linux-kernel - [PATCH] fix /proc/partitions oops

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Date:	Thu, 7 Sep 2006 17:04:20 +0100 (BST)
From:	James Cross <james_cross@...antec.com>
To:	Andrew Morton <akpm@...l.org>
cc:	Jens Axboe <axboe@...e.de>,
	Andries Brouwer <Andries.Brouwer@....nl>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] fix /proc/partitions oops

If show_partition happens to race with re-reading a partition table
(rescan_partitions), sgp->part[n] can become NULL just after it's been
tested, and so cause an oops: read it once (and read nr_sects just the
once too, to avoid a chance of showing 0).

Signed-off-by: James Cross <james_cross@...antec.com>
---

 block/genhd.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- 2.6.18-rc6/block/genhd.c.orig	2006-09-07 12:14:32.183218000 +0100
+++ 2.6.18-rc6/block/genhd.c	2006-09-07 12:15:16.134498000 +0100
@@ -261,14 +261,18 @@ static int show_partition(struct seq_fil
 		(unsigned long long)get_capacity(sgp) >> 1,
 		disk_name(sgp, 0, buf));
 	for (n = 0; n < sgp->minors - 1; n++) {
-		if (!sgp->part[n])
+		struct hd_struct *partn;
+		unsigned long long nr_sects;
+
+		partn = sgp->part[n];
+		if (!partn)
 			continue;
-		if (sgp->part[n]->nr_sects == 0)
+		nr_sects = partn->nr_sects;
+		if (nr_sects == 0)
 			continue;
 		seq_printf(part, "%4d  %4d %10llu %s\n",
 			sgp->major, n + 1 + sgp->first_minor,
-			(unsigned long long)sgp->part[n]->nr_sects >> 1 ,
-			disk_name(sgp, n + 1, buf));
+			nr_sects >> 1, disk_name(sgp, n + 1, buf));
 	}
 
 	return 0;
-
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