Syzbot reported a BUG in ext4_free_blocks. The issue is triggered from ext4_mb_clear_bb(). What happens is the block number passed to ext4_get_group_no_and_offset() is 0 and the es->s_first_data_block is 1. This makes block group number returned from ext4_get_group_no_and_offset equal to -1. This is then passed to ext4_get_group_info() and hits a BUG: BUG_ON(group >= EXT4_SB(sb)->s_groups_count), what can be seen in the trace below. This patch adds an assertion to ext4_get_group_no_and_offset() that checks if block number is not smaller than es->s_first_data_block. kernel BUG at fs/ext4/ext4.h:3319! invalid opcode: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 337 Comm: repro Not tainted 5.19.0-rc6-00105-g4e8e898e4107-dirty #14 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014 RIP: 0010:ext4_mb_clear_bb+0x1bd6/0x1be0 Call Trace: <TASK> ext4_free_blocks+0x9b3/0xc90 ext4_clear_blocks+0x344/0x3b0 ext4_ind_truncate+0x967/0x1050 ext4_truncate+0xb1b/0x1210 ext4_evict_inode+0xf06/0x16f0 evict+0x2a3/0x630 iput+0x618/0x850 ext4_enable_quotas+0x578/0x920 ext4_orphan_cleanup+0x539/0x1200 ext4_fill_super+0x94d8/0x9bc0 get_tree_bdev+0x40c/0x630 ext4_get_tree+0x1c/0x20 vfs_get_tree+0x88/0x290 do_new_mount+0x289/0xac0 path_mount+0x607/0xfd0 __se_sys_mount+0x2c4/0x3b0 __x64_sys_mount+0xbf/0xd0 do_syscall_64+0x3d/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd </TASK> Link: https://syzkaller.appspot.com/bug?id=5266d464285a03cee9dbfda7d2452a72c3c2ae7c Reported-by: syzbot+15cd994e273307bf5cfa@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Tadeusz Struk <tadeusz.struk@xxxxxxxxxx> --- fs/ext4/balloc.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c index 78ee3ef795ae..1175750ad05f 100644 --- a/fs/ext4/balloc.c +++ b/fs/ext4/balloc.c @@ -56,6 +56,9 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr, struct ext4_super_block *es = EXT4_SB(sb)->s_es; ext4_grpblk_t offset; + if (blocknr < le32_to_cpu(es->s_first_data_block)) + blocknr = le32_to_cpu(es->s_first_data_block); + blocknr = blocknr - le32_to_cpu(es->s_first_data_block); offset = do_div(blocknr, EXT4_BLOCKS_PER_GROUP(sb)) >> EXT4_SB(sb)->s_cluster_bits; -- 2.36.1
