[PATCH AUTOSEL 5.19 63/64] ext4: block range must be validated before use in ext4_mb_clear_bb()

Sasha Levin
2022-08-14T15:35:15Z

From: Lukas Czerner <lczerner@redhat.com>

[ Upstream commit 1e1c2b86ef86a8477fd9b9a4f48a6bfe235606f6 ]

Block range to free is validated in ext4_free_blocks() using
ext4_inode_block_valid() and then it's passed to ext4_mb_clear_bb().
However in some situations on bigalloc file system the range might be
adjusted after the validation in ext4_free_blocks() which can lead to
troubles on corrupted file systems such as one found by syzkaller that
resulted in the following BUG

kernel BUG at fs/ext4/ext4.h:3319!
PREEMPT SMP NOPTI
CPU: 28 PID: 4243 Comm: repro Kdump: loaded Not tainted 5.19.0-rc6+ #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014
RIP: 0010:ext4_free_blocks+0x95e/0xa90
Call Trace:
<TASK>
? lock_timer_base+0x61/0x80
? __es_remove_extent+0x5a/0x760
? __mod_timer+0x256/0x380
? ext4_ind_truncate_ensure_credits+0x90/0x220
ext4_clear_blocks+0x107/0x1b0
ext4_free_data+0x15b/0x170
ext4_ind_truncate+0x214/0x2c0
? _raw_spin_unlock+0x15/0x30
? ext4_discard_preallocations+0x15a/0x410
? ext4_journal_check_start+0xe/0x90
? __ext4_journal_start_sb+0x2f/0x110
ext4_truncate+0x1b5/0x460
? __ext4_journal_start_sb+0x2f/0x110
ext4_evict_inode+0x2b4/0x6f0
evict+0xd0/0x1d0
ext4_enable_quotas+0x11f/0x1f0
ext4_orphan_cleanup+0x3de/0x430
? proc_create_seq_private+0x43/0x50
ext4_fill_super+0x295f/0x3ae0
? snprintf+0x39/0x40
? sget_fc+0x19c/0x330
? ext4_reconfigure+0x850/0x850
get_tree_bdev+0x16d/0x260
vfs_get_tree+0x25/0xb0
path_mount+0x431/0xa70
__x64_sys_mount+0xe2/0x120
do_syscall_64+0x5b/0x80
? do_user_addr_fault+0x1e2/0x670
? exc_page_fault+0x70/0x170
entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7fdf4e512ace

Fix it by making sure that the block range is properly validated before
used every time it changes in ext4_free_blocks() or ext4_mb_clear_bb().

Link: https://syzkaller.appspot.com/bug?id=5266d464285a03cee9dbfda7d2452a72c3c2ae7c
Reported-by: syzbot+15cd994e273307bf5cfa@syzkaller.appspotmail.com
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Cc: Tadeusz Struk <tadeusz.struk@linaro.org>
Tested-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Link: https://lore.kernel.org/r/20220714165903.58260-1-lczerner@redhat.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/mballoc.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 9e06334771a3..38e7dc2531b1 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -5928,6 +5928,15 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,

sbi = EXT4_SB(sb);

+ if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
+ !ext4_inode_block_valid(inode, block, count)) {
+ ext4_error(sb, "Freeing blocks in system zone - "
+ "Block = %llu, count = %lu", block, count);
+ /* err = 0. ext4_std_error should be a no op */
+ goto error_return;
+ }
+ flags |= EXT4_FREE_BLOCKS_VALIDATED;
+
do_more:
overflow = 0;
ext4_get_group_no_and_offset(sb, block, &block_group, &bit);
@@ -5944,6 +5953,8 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
overflow = EXT4_C2B(sbi, bit) + count -
EXT4_BLOCKS_PER_GROUP(sb);
count -= overflow;
+ /* The range changed so it's no longer validated */
+ flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
}
count_clusters = EXT4_NUM_B2C(sbi, count);
bitmap_bh = ext4_read_block_bitmap(sb, block_group);
@@ -5958,7 +5969,8 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
goto error_return;
}

- if (!ext4_inode_block_valid(inode, block, count)) {
+ if (!(flags & EXT4_FREE_BLOCKS_VALIDATED) &&
+ !ext4_inode_block_valid(inode, block, count)) {
ext4_error(sb, "Freeing blocks in system zone - "
"Block = %llu, count = %lu", block, count);
/* err = 0. ext4_std_error should be a no op */
@@ -6081,6 +6093,8 @@ static void ext4_mb_clear_bb(handle_t *handle, struct inode *inode,
block += count;
count = overflow;
put_bh(bitmap_bh);
+ /* The range changed so it's no longer validated */
+ flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
goto do_more;
}
error_return:
@@ -6127,6 +6141,7 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
"block = %llu, count = %lu", block, count);
return;
}
+ flags |= EXT4_FREE_BLOCKS_VALIDATED;

ext4_debug("freeing block %llu\n", block);
trace_ext4_free_blocks(inode, block, count, flags);
@@ -6158,6 +6173,8 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
block -= overflow;
count += overflow;
}
+ /* The range changed so it's no longer validated */
+ flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
}
overflow = EXT4_LBLK_COFF(sbi, count);
if (overflow) {
@@ -6168,6 +6185,8 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
return;
} else
count += sbi->s_cluster_ratio - overflow;
+ /* The range changed so it's no longer validated */
+ flags &= ~EXT4_FREE_BLOCKS_VALIDATED;
}

if (!bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
--
2.35.1