Re: [PATCH v2] ext4: fix WARNING in mb_find_extent

"yebin (H)" <yebin10@xxxxxxxxxx> · Fri, 3 Mar 2023 09:13:10 +0800

ping...

On 2023/1/16 10:00, Ye Bin wrote:
From: Ye Bin <yebin10@xxxxxxxxxx>

Syzbot found the following issue:

EXT4-fs: Warning: mounting with data=journal disables delayed allocation, dioread_nolock, O_DIRECT and fast_commit support!
EXT4-fs (loop0): orphan cleanup on readonly fs
------------[ cut here ]------------
WARNING: CPU: 1 PID: 5067 at fs/ext4/mballoc.c:1869 mb_find_extent+0x8a1/0xe30
Modules linked in:
CPU: 1 PID: 5067 Comm: syz-executor307 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:mb_find_extent+0x8a1/0xe30 fs/ext4/mballoc.c:1869
RSP: 0018:ffffc90003c9e098 EFLAGS: 00010293
RAX: ffffffff82405731 RBX: 0000000000000041 RCX: ffff8880783457c0
RDX: 0000000000000000 RSI: 0000000000000041 RDI: 0000000000000040
RBP: 0000000000000040 R08: ffffffff82405723 R09: ffffed10053c9402
R10: ffffed10053c9402 R11: 1ffff110053c9401 R12: 0000000000000000
R13: ffffc90003c9e538 R14: dffffc0000000000 R15: ffffc90003c9e2cc
FS:  0000555556665300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056312f6796f8 CR3: 0000000022437000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  <TASK>
  ext4_mb_complex_scan_group+0x353/0x1100 fs/ext4/mballoc.c:2307
  ext4_mb_regular_allocator+0x1533/0x3860 fs/ext4/mballoc.c:2735
  ext4_mb_new_blocks+0xddf/0x3db0 fs/ext4/mballoc.c:5605
  ext4_ext_map_blocks+0x1868/0x6880 fs/ext4/extents.c:4286
  ext4_map_blocks+0xa49/0x1cc0 fs/ext4/inode.c:651
  ext4_getblk+0x1b9/0x770 fs/ext4/inode.c:864
  ext4_bread+0x2a/0x170 fs/ext4/inode.c:920
  ext4_quota_write+0x225/0x570 fs/ext4/super.c:7105
  write_blk fs/quota/quota_tree.c:64 [inline]
  get_free_dqblk+0x34a/0x6d0 fs/quota/quota_tree.c:130
  do_insert_tree+0x26b/0x1aa0 fs/quota/quota_tree.c:340
  do_insert_tree+0x722/0x1aa0 fs/quota/quota_tree.c:375
  do_insert_tree+0x722/0x1aa0 fs/quota/quota_tree.c:375
  do_insert_tree+0x722/0x1aa0 fs/quota/quota_tree.c:375
  dq_insert_tree fs/quota/quota_tree.c:401 [inline]
  qtree_write_dquot+0x3b6/0x530 fs/quota/quota_tree.c:420
  v2_write_dquot+0x11b/0x190 fs/quota/quota_v2.c:358
  dquot_acquire+0x348/0x670 fs/quota/dquot.c:444
  ext4_acquire_dquot+0x2dc/0x400 fs/ext4/super.c:6740
  dqget+0x999/0xdc0 fs/quota/dquot.c:914
  __dquot_initialize+0x3d0/0xcf0 fs/quota/dquot.c:1492
  ext4_process_orphan+0x57/0x2d0 fs/ext4/orphan.c:329
  ext4_orphan_cleanup+0xb60/0x1340 fs/ext4/orphan.c:474
  __ext4_fill_super fs/ext4/super.c:5516 [inline]
  ext4_fill_super+0x81cd/0x8700 fs/ext4/super.c:5644
  get_tree_bdev+0x400/0x620 fs/super.c:1282
  vfs_get_tree+0x88/0x270 fs/super.c:1489
  do_new_mount+0x289/0xad0 fs/namespace.c:3145
  do_mount fs/namespace.c:3488 [inline]
  __do_sys_mount fs/namespace.c:3697 [inline]
  __se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3674
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Add some debug information:
mb_find_extent: mb_find_extent block=41, order=0 needed=64 next=0 ex=0/41/1@3735929054 64 64 7
block_bitmap: ff 3f 0c 00 fc 01 00 00 d2 3d 00 00 00 00 00 00 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

Acctually, blocks per group is 64, but block bitmap indicate at least has
128 blocks. Now, ext4_validate_block_bitmap() didn't check invalid block's
bitmap if set.
To resolve above issue, add check like fsck "Padding at end of block bitmap is
not set".

Reported-by: syzbot+68223fe9f6c95ad43bed@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
---
  fs/ext4/balloc.c | 25 +++++++++++++++++++++++++
  1 file changed, 25 insertions(+)

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 8ff4b9192a9f..f2c415f31b75 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -303,6 +303,22 @@ struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
  	return desc;
  }
  
+static ext4_fsblk_t ext4_valid_block_bitmap_padding(struct super_block *sb,
+						    ext4_group_t block_group,
+						    struct buffer_head *bh)
+{
+	ext4_grpblk_t next_zero_bit;
+	unsigned long bitmap_size = sb->s_blocksize * 8;
+	unsigned int offset = num_clusters_in_group(sb, block_group);
+
+	if (bitmap_size <= offset)
+		return 0;
+
+	next_zero_bit = ext4_find_next_zero_bit(bh->b_data, bitmap_size, offset);
+
+	return (next_zero_bit < bitmap_size ? next_zero_bit : 0);
+}
+
  /*
   * Return the block number which was discovered to be invalid, or 0 if
   * the block bitmap is valid.
@@ -401,6 +417,15 @@ static int ext4_validate_block_bitmap(struct super_block *sb,
  					EXT4_GROUP_INFO_BBITMAP_CORRUPT);
  		return -EFSCORRUPTED;
  	}
+	blk = ext4_valid_block_bitmap_padding(sb, block_group, bh);
+	if (unlikely(blk != 0)) {
+		ext4_unlock_group(sb, block_group);
+		ext4_error(sb, "bg %u: block %llu: padding at end of block bitmap is not set",
+			   block_group, blk);
+		ext4_mark_group_bitmap_corrupted(sb, block_group,
+						 EXT4_GROUP_INFO_BBITMAP_CORRUPT);
+		return -EFSCORRUPTED;
+	}
  	set_buffer_verified(bh);
  verified:
  	ext4_unlock_group(sb, block_group);







