[PATCH] xfs: add agf freeblocks verify in xfs_agf_verify

[Zheng Bin <zhengbin13@huawei.com>]

We recently used fuzz(hydra) to test XFS and automatically generate
tmp.img(XFS v5 format, but some metadata is wrong)

Test as follows:
mount tmp.img tmpdir
cp file1M tmpdir
sync

tmpdir/file1M size is 1M, but its data can not sync to disk.

This is because tmp.img has some problems, using xfs_repair detect
information as follows:

agf_freeblks 0, counted 3224 in ag 0
agf_longest 536874136, counted 3224 in ag 0
sb_fdblocks 613, counted 3228

Add these agf freeblocks checks:
1. agf_longest < agf_freeblks
2. agf_freeblks < sb_fdblocks

Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Ren Xudong <renxudong1@huawei.com>
---
 fs/xfs/libxfs/xfs_alloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index d8053bc..0f4b4d1 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -2858,6 +2858,10 @@ xfs_agf_verify(
 	      be32_to_cpu(agf->agf_flcount) <= xfs_agfl_size(mp)))
 		return __this_address;

+	if (be32_to_cpu(agf->agf_freeblks) < be32_to_cpu(agf->agf_longest) ||
+	    be32_to_cpu(agf->agf_freeblks) >= mp->m_sb.sb_fdblocks)
+		return __this_address;
+
 	if (be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) < 1 ||
 	    be32_to_cpu(agf->agf_levels[XFS_BTNUM_CNT]) < 1 ||
 	    be32_to_cpu(agf->agf_levels[XFS_BTNUM_BNO]) > XFS_BTREE_MAXLEVELS ||
--
2.7.4