Re: [PATCH v2] udf: Check consistency of Space Bitmap Descriptor

[Jan Kara <jack@suse.cz>]

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On Thu 02-02-23 17:04:56, Vladislav Efanov wrote:
> Bits, which are related to Bitmap Descriptor logical blocks,
> are not reset when buffer headers are allocated for them. As the
> result, these logical blocks can be treated as free and
> be used for other blocks.This can cause usage of one buffer header
> for several types of data. UDF issues WARNING in this situation:
> 
> WARNING: CPU: 0 PID: 2703 at fs/udf/inode.c:2014
>   __udf_add_aext+0x685/0x7d0 fs/udf/inode.c:2014
> 
> RIP: 0010:__udf_add_aext+0x685/0x7d0 fs/udf/inode.c:2014
> Call Trace:
>  udf_setup_indirect_aext+0x573/0x880 fs/udf/inode.c:1980
>  udf_add_aext+0x208/0x2e0 fs/udf/inode.c:2067
>  udf_insert_aext fs/udf/inode.c:2233 [inline]
>  udf_update_extents fs/udf/inode.c:1181 [inline]
>  inode_getblk+0x1981/0x3b70 fs/udf/inode.c:885
> 
> Found by Linux Verification Center (linuxtesting.org) with syzkaller.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Vladislav Efanov <VEfanov@ispras.ru>
> ---
> v2: Do not clear bits related to Bitmap Descriptor logical blocks,
> but return -EFSCORRUPTED error instead.
>  fs/udf/balloc.c  | 24 ++++++++++++++++++++++++
>  fs/udf/udfdecl.h |  1 +
>  2 files changed, 25 insertions(+)

Thanks for the fix!

>  	bitmap->s_block_bitmap[bitmap_nr] = bh;
> +	/* Check consistency of Space Bitmap buffer. */
> +	if (bh) {
> +		max_bits_others = sb->s_blocksize * 8;
> +		max_bits_1st = max_bits_others - (sizeof(struct spaceBitmapDesc) << 3);
> +		rest_bits = (bitmap->s_nr_groups > max_bits_1st) ?
> +					bitmap->s_nr_groups - max_bits_1st : 0;
> +		if (!bitmap_nr)
> +			max_bits = min(max_bits_1st, bitmap->s_nr_groups);
> +		else if (bitmap_nr < rest_bits / max_bits_others + 1)
> +			max_bits = max_bits_others;

So this should be using DIV_ROUND_UP() instead of plain division and + 1
AFAICT. Anyway, I've somewhat simplified these conditions to make things a
bit more obvious and applied your patch. The result is attached for your
reference.

> +		else if (bitmap_nr == rest_bits / max_bits_others + 1)
> +			max_bits = rest_bits % max_bits_others;
> +		for (i = 0; i < max_bits; i++) {
> +			if (udf_test_bit(i + (bitmap_nr ? 0 :
> +				(sizeof(struct spaceBitmapDesc) << 3)),
> +				 bh->b_data))
> +				return -EFSCORRUPTED;
> +		}
> +	}


								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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From 1e0d4adf17e7ef03281d7b16555e7c1508c8ed2d Mon Sep 17 00:00:00 2001
From: Vladislav Efanov <VEfanov@ispras.ru>
Date: Thu, 2 Feb 2023 17:04:56 +0300
Subject: [PATCH] udf: Check consistency of Space Bitmap Descriptor

Bits, which are related to Bitmap Descriptor logical blocks,
are not reset when buffer headers are allocated for them. As the
result, these logical blocks can be treated as free and
be used for other blocks.This can cause usage of one buffer header
for several types of data. UDF issues WARNING in this situation:

WARNING: CPU: 0 PID: 2703 at fs/udf/inode.c:2014
  __udf_add_aext+0x685/0x7d0 fs/udf/inode.c:2014

RIP: 0010:__udf_add_aext+0x685/0x7d0 fs/udf/inode.c:2014
Call Trace:
 udf_setup_indirect_aext+0x573/0x880 fs/udf/inode.c:1980
 udf_add_aext+0x208/0x2e0 fs/udf/inode.c:2067
 udf_insert_aext fs/udf/inode.c:2233 [inline]
 udf_update_extents fs/udf/inode.c:1181 [inline]
 inode_getblk+0x1981/0x3b70 fs/udf/inode.c:885

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

[JK: Somewhat cleaned up the boundary checks]

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Vladislav Efanov <VEfanov@ispras.ru>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/udf/balloc.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index cdf90928b7f2..14b9db4c80f0 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -36,18 +36,41 @@ static int read_block_bitmap(struct super_block *sb,
 			     unsigned long bitmap_nr)
 {
 	struct buffer_head *bh = NULL;
-	int retval = 0;
+	int i;
+	int max_bits, off, count;
 	struct kernel_lb_addr loc;
 
 	loc.logicalBlockNum = bitmap->s_extPosition;
 	loc.partitionReferenceNum = UDF_SB(sb)->s_partition;
 
 	bh = sb_bread(sb, udf_get_lb_pblock(sb, &loc, block));
+	bitmap->s_block_bitmap[bitmap_nr] = bh;
 	if (!bh)
-		retval = -EIO;
+		return -EIO;
 
-	bitmap->s_block_bitmap[bitmap_nr] = bh;
-	return retval;
+	/* Check consistency of Space Bitmap buffer. */
+	max_bits = sb->s_blocksize * 8;
+	if (!bitmap_nr) {
+		off = sizeof(struct spaceBitmapDesc) << 3;
+		count = min(max_bits - off, bitmap->s_nr_groups);
+	} else {
+		/*
+		 * Rough check if bitmap number is too big to have any bitmap
+ 		 * blocks reserved.
+		 */
+		if (bitmap_nr >
+		    (bitmap->s_nr_groups >> (sb->s_blocksize_bits + 3)) + 2)
+			return 0;
+		off = 0;
+		count = bitmap->s_nr_groups - bitmap_nr * max_bits +
+				(sizeof(struct spaceBitmapDesc) << 3);
+		count = min(count, max_bits);
+	}
+
+	for (i = 0; i < count; i++)
+		if (udf_test_bit(i + off, bh->b_data))
+			return -EFSCORRUPTED;
+	return 0;
 }
 
 static int __load_block_bitmap(struct super_block *sb,
-- 
2.35.3