linux-kernel - [PATCH AUTOSEL 4.18 09/56] isofs: reject hardware sector size

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Date:   Thu, 20 Sep 2018 02:47:32 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Eric Sandeen <sandeen@...hat.com>, Jan Kara <jack@...e.cz>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 09/56] isofs: reject hardware sector size > 2048
 bytes

From: Eric Sandeen <sandeen@...hat.com>

[ Upstream commit 09a4e0be5826aa66c4ce9954841f110ffe63ef4f ]

The largest block size supported by isofs is ISOFS_BLOCK_SIZE (2048), but
isofs_fill_super calls sb_min_blocksize and sets the blocksize to the
device's logical block size if it's larger than what we ended up with after
option parsing.

If for some reason we try to mount a hard 4k device as an isofs filesystem,
we'll set opt.blocksize to 4096, and when we try to read the superblock
we found via:

        block = iso_blknum << (ISOFS_BLOCK_BITS - s->s_blocksize_bits)

with s_blocksize_bits greater than ISOFS_BLOCK_BITS, we'll have a negative
shift and the bread will fail somewhat cryptically:

  isofs_fill_super: bread failed, dev=sda, iso_blknum=17, block=-2147483648

It seems best to just catch and clearly reject mounts of such a device.

Reported-by: Bryan Gurney <bgurney@...hat.com>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 fs/isofs/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/isofs/inode.c b/fs/isofs/inode.c
index ec3fba7d492f..488a9e7f8f66 100644
--- a/fs/isofs/inode.c
+++ b/fs/isofs/inode.c
@@ -24,6 +24,7 @@
 #include <linux/mpage.h>
 #include <linux/user_namespace.h>
 #include <linux/seq_file.h>
+#include <linux/blkdev.h>
 
 #include "isofs.h"
 #include "zisofs.h"
@@ -653,6 +654,12 @@ static int isofs_fill_super(struct super_block *s, void *data, int silent)
 	/*
 	 * What if bugger tells us to go beyond page size?
 	 */
+	if (bdev_logical_block_size(s->s_bdev) > 2048) {
+		printk(KERN_WARNING
+		       "ISOFS: unsupported/invalid hardware sector size %d\n",
+			bdev_logical_block_size(s->s_bdev));
+		goto out_freesbi;
+	}
 	opt.blocksize = sb_min_blocksize(s, opt.blocksize);
 
 	sbi->s_high_sierra = 0; /* default is iso9660 */
-- 
2.17.1