[PATCH 2/2] ext4: add inode table check in __ext4_get_inode_loc to aovid possible infinite loop

Baokun Li
2022-08-17T13:16:22Z

In do_writepages, if the value returned by ext4_writepages is "-ENOMEM"
and "wbc->sync_mode == WB_SYNC_ALL", retry until the condition is not met.

In __ext4_get_inode_loc, if the bh returned by sb_getblk is NULL,
the function returns -ENOMEM.

In __getblk_slow, if the return value of grow_buffers is less than 0,
the function returns NULL.

When the three processes are connected in series like the following stack,
an infinite loop may occur:

do_writepages <--- keep retrying
ext4_writepages
mpage_map_and_submit_extent
mpage_map_one_extent
ext4_map_blocks
ext4_ext_map_blocks
ext4_ext_handle_unwritten_extents
ext4_ext_convert_to_initialized
ext4_split_extent
ext4_split_extent_at
__ext4_ext_dirty
__ext4_mark_inode_dirty
ext4_reserve_inode_write
ext4_get_inode_loc
__ext4_get_inode_loc <--- return -ENOMEM
sb_getblk
__getblk_gfp
__getblk_slow <--- return NULL
grow_buffers
grow_dev_page <--- return -ENXIO
ret = (block < end_block) ? 1 : -ENXIO;

In this issue, bg_inode_table_hi is overwritten as an incorrect value.
As a result, `block < end_block` cannot be met in grow_dev_page.
Therefore, __ext4_get_inode_loc always returns '-ENOMEM' and do_writepages
keeps retrying. As a result, the writeback process is in the D state due
to an infinite loop.

Add a check on inode table block in the __ext4_get_inode_loc function by
referring to ext4_read_inode_bitmap to avoid this infinite loop.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
fs/ext4/inode.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 601214453c3a..5e171879fa23 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4466,9 +4466,17 @@ static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
inodes_per_block = EXT4_SB(sb)->s_inodes_per_block;
inode_offset = ((ino - 1) %
EXT4_INODES_PER_GROUP(sb));
- block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);

+ block = ext4_inode_table(sb, gdp);
+ if ((block <= le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) ||
+ (block >= ext4_blocks_count(EXT4_SB(sb)->s_es))) {
+ ext4_error(sb, "Invalid inode table block %llu in "
+ "block_group %u", block, iloc->block_group);
+ return -EFSCORRUPTED;
+ }
+ block += (inode_offset / inodes_per_block);
+
bh = sb_getblk(sb, block);
if (unlikely(!bh))
return -ENOMEM;
--
2.31.1