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Subject[PATCH] ext4: fix kernel BUG in ext4_free_blocks
Date
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@syzkaller.appspotmail.com
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
---
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
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