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ocfs2: check tl_used after reading it from trancate log inode

The fuzz image has a truncate log inode whose tl_used is bigger than
tl_count so it triggers the BUG in ocfs2_truncate_log_needs_flush() [1].

As what the check in ocfs2_truncate_log_needs_flush() does, just do same
check into ocfs2_get_truncate_log_info() when truncate log inode is
reading in so we can bail out earlier.

[1]
(syz.0.17,5491,0):ocfs2_truncate_log_needs_flush:5830 ERROR: bug expression: le16_to_cpu(tl->tl_used) > le16_to_cpu(tl->tl_count)
kernel BUG at fs/ocfs2/alloc.c:5830!
RIP: 0010:ocfs2_truncate_log_needs_flush fs/ocfs2/alloc.c:5827 [inline]
Call Trace:
ocfs2_commit_truncate+0xb64/0x21d0 fs/ocfs2/alloc.c:7372
ocfs2_truncate_file+0xca2/0x1420 fs/ocfs2/file.c:509
ocfs2_setattr+0x1520/0x1b40 fs/ocfs2/file.c:1212
notify_change+0xc1a/0xf40 fs/attr.c:546
do_truncate+0x1a4/0x220 fs/open.c:68

Link: https://lkml.kernel.org/r/tencent_B24B1C1BE225DCBA44BB6933AB9E1B1B0708@qq.com
Reported-by: syzbot+f82afc4d4e74d0ef7a89@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f82afc4d4e74d0ef7a89
Tested-by: syzbot+f82afc4d4e74d0ef7a89@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Edward Adam Davis and committed by
Andrew Morton 4ac577ae b2135d1c

+4 -2
+4 -2
fs/ocfs2/alloc.c
··· 6164 6164 struct buffer_head *bh = NULL; 6165 6165 struct ocfs2_dinode *di; 6166 6166 struct ocfs2_truncate_log *tl; 6167 - unsigned int tl_count; 6167 + unsigned int tl_count, tl_used; 6168 6168 6169 6169 inode = ocfs2_get_system_file_inode(osb, 6170 6170 TRUNCATE_LOG_SYSTEM_INODE, ··· 6185 6185 di = (struct ocfs2_dinode *)bh->b_data; 6186 6186 tl = &di->id2.i_dealloc; 6187 6187 tl_count = le16_to_cpu(tl->tl_count); 6188 + tl_used = le16_to_cpu(tl->tl_used); 6188 6189 if (unlikely(tl_count > ocfs2_truncate_recs_per_inode(osb->sb) || 6189 - tl_count == 0)) { 6190 + tl_count == 0 || 6191 + tl_used > tl_count)) { 6190 6192 status = -EFSCORRUPTED; 6191 6193 iput(inode); 6192 6194 brelse(bh);