ocfs2: adjust ocfs2_xa_remove_entry() to match UBSAN boundary checks

After introducing 2f26f58df041 ("ocfs2: annotate flexible array members
with __counted_by_le()"), syzbot has reported the following issue:

UBSAN: array-index-out-of-bounds in fs/ocfs2/xattr.c:1955:3
index 2 is out of range for type 'struct ocfs2_xattr_entry[]
__counted_by(xh_count)' (aka 'struct ocfs2_xattr_entry[]')
...
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
 __ubsan_handle_out_of_bounds+0xe9/0xf0 lib/ubsan.c:455
 ocfs2_xa_remove_entry+0x36d/0x3e0 fs/ocfs2/xattr.c:1955
 ...

To address this issue, 'xh_entries[]' member removal should be performed
before actually changing 'xh_count', thus making sure that all array
accesses matches the boundary checks performed by UBSAN.

Link: https://lkml.kernel.org/r/20251211155949.774485-1-dmantipov@yandex.ru
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reported-by: syzbot+cf96bc82a588a27346a8@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=cf96bc82a588a27346a8
Reviewed-by: Heming Zhao <heming.zhao@suse.com>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Deepanshu Kartikey <kartikey406@gmail.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index 1b21fbc16d73a2d727d4b4a36c249d1c41db4297..5fd85f51786898fffafd4c2500dff65107cd5a83 100644 (file)
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -1971,8 +1971,7 @@ static void ocfs2_xa_remove_entry(struct ocfs2_xa_loc *loc)
        ocfs2_xa_wipe_namevalue(loc);
        loc->xl_entry = NULL;
 
-       le16_add_cpu(&xh->xh_count, -1);
-       count = le16_to_cpu(xh->xh_count);
+       count = le16_to_cpu(xh->xh_count) - 1;
 
        /*
         * Only zero out the entry if there are more remaining.  This is
@@ -1987,6 +1986,8 @@ static void ocfs2_xa_remove_entry(struct ocfs2_xa_loc *loc)
                memset(&xh->xh_entries[count], 0,
                       sizeof(struct ocfs2_xattr_entry));
        }
+
+       xh->xh_count = cpu_to_le16(count);
 }
 
 /*