[PATCH] udf: Reserve bits for Bitmap Descriptor buffers

[Vladislav Efanov <VEfanov@ispras.ru>]

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>
---
 fs/udf/balloc.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c
index 8e597db4d971..52dab5b63715 100644
--- a/fs/udf/balloc.c
+++ b/fs/udf/balloc.c
@@ -37,6 +37,7 @@ static int read_block_bitmap(struct super_block *sb,
 {
 	struct buffer_head *bh = NULL;
 	int retval = 0;
+	int i;
 	struct kernel_lb_addr loc;
 
 	loc.logicalBlockNum = bitmap->s_extPosition;
@@ -47,6 +48,12 @@ static int read_block_bitmap(struct super_block *sb,
 		retval = -EIO;
 
 	bitmap->s_block_bitmap[bitmap_nr] = bh;
+	/* Reserve bits for Space Bitmap buffer headers. */
+	if (bh && !bitmap_nr)
+		for (i = 0; i < bitmap->s_nr_groups; i++)
+			udf_clear_bit(bitmap->s_extPosition + i +
+				      (sizeof(struct spaceBitmapDesc) << 3),
+				      bh->b_data);
 	return retval;
 }
 
-- 
2.34.1