Subject: ext4: block range must be validated before use in ext4_mb_clear_bb()

[Tadeusz Struk]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

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)) {
-- 2.35.3

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+15cd99...@syzkaller.appspotmail.com

Tested on:

commit: 4a57a840 vf/remap: return the amount of bytes actually..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=130af58a080000
kernel config: https://syzkaller.appspot.com/x/.config?x=416bd8aed6ca51ae
dashboard link: https://syzkaller.appspot.com/bug?extid=15cd994e273307bf5cfa
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
patch: https://syzkaller.appspot.com/x/patch.diff?x=13622dd0080000

Note: testing is done by a robot and is best-effort only.