linux-kernel - [PATCH] block: Fix the maximum minor value is blk_alloc_ext

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <cc17199798312406b90834e433d2cefe8266823d.1648306232.git.christophe.jaillet@wanadoo.fr>
Date:   Sat, 26 Mar 2022 15:50:46 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>,
        Jan Kara <jack@...e.cz>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux-block@...r.kernel.org
Subject: [PATCH] block: Fix the maximum minor value is blk_alloc_ext_minor()

ida_alloc_range(..., min, max, ...) returns values from min to max,
inclusive.

So, NR_EXT_DEVT is a valid idx returned by blk_alloc_ext_minor().

This is an issue because in device_add_disk(), this value is used in:
   ddev->devt = MKDEV(disk->major, disk->first_minor);
and NR_EXT_DEVT is '(1 << MINORBITS)'.

So, should 'disk->first_minor' be NR_EXT_DEVT, it would overflow.

Fixes: 22ae8ce8b892 ("block: simplify bdev/disk lookup in blkdev_get")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
#define MKDEV(ma,mi)	(((ma) << MINORBITS) | (mi))

This patch is completely speculative, but it seems that idr_alloc() and
ida_alloc_range() don't have the same semantic regarding the upper bound.
idr_alloc() looks exclusive, while ida_alloc_range() is inclusive.

We changed from the first one to the other one in the commit in Fixes:.
---
 block/genhd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index c9a4fc90d3e9..b8b6759d670f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -335,7 +335,7 @@ int blk_alloc_ext_minor(void)
 {
 	int idx;

-	idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
+	idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT - 1, GFP_KERNEL);
 	if (idx == -ENOSPC)
 		return -EBUSY;
 	return idx;
-- 
2.32.0