[PATCH] bfs: Fix sanity checks for empty files

[Rakesh Pandit]

Mount fails if file system image has empty files because of sanity
check while reading superblock. For empty files disk offset to end of
file (i_eoffset) is cpu_to_le32(-1). Sanity check comparison, which
compares disk offset with file system size isn't valid for this value
and hence is ignored with this patch.

Steps to reproduce:

$  dd if=/dev/zero of=bfs-image count=204800
$  mkfs.bfs bfs-image
$  mkdir bfs-mount-point
$  sudo mount -t bfs -o loop bfs-image bfs-mount-point/
$  cd bfs-mount-point/
$  sudo touch a
$  cd ..
$  sudo umount bfs-mount-point/
$  sudo mount -t bfs -o loop bfs-image bfs-mount-point/
mount: /dev/loop0: can't read superblock

$  dmesg
[25526.689580] BFS-fs: bfs_fill_super(): Inode 0x00000003 corrupted

Signed-off-by: Rakesh Pandit <rakesh@xxxxxxxxxx>
---

This was sent three years but maintainer has been unresponsive:
https://marc.info/?l=linux-kernel&m=138980764525250

So sending you Andrew as previous patches to bfs have gone through
your tree.  This is tested and reproducible.

 fs/bfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/bfs/inode.c b/fs/bfs/inode.c
index f2deec0..0d3dc18 100644
--- a/fs/bfs/inode.c
+++ b/fs/bfs/inode.c
@@ -419,7 +419,7 @@ static int bfs_fill_super(struct super_block *s, void *data, int silent)
 		if (i_sblock > info->si_blocks ||
 			i_eblock > info->si_blocks ||
 			i_sblock > i_eblock ||
-			i_eoff > s_size ||
+			(i_eoff != le32_to_cpu(-1) && i_eoff > s_size) ||
 			i_sblock * BFS_BSIZE > i_eoff) {
 
 			printf("Inode 0x%08x corrupted\n", i);
-- 
2.9.3