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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Jan Kara <jack@suse.cz>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.15 855/913] block: Fix the maximum minor value is blk_alloc_ext_minor()
Date:   Tue,  5 Apr 2022 09:31:57 +0200
Message-Id: <20220405070405.457347488@linuxfoundation.org>
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From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>

commit d1868328dec5ae2cf210111025fcbc71f78dd5ca upstream.

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@wanadoo.fr>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/cc17199798312406b90834e433d2cefe8266823d.1648306232.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 block/genhd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/genhd.c
+++ b/block/genhd.c
@@ -324,7 +324,7 @@ 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;