From 9056d6489f5a41cfbb67f719d2c0ce61ead72d9f Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@kernel.org>
Date: Mon, 6 Dec 2021 22:44:19 +0800
Subject: [PATCH] f2fs: fix to do sanity check on inode type during garbage collection
Git-commit: 9056d6489f5a41cfbb67f719d2c0ce61ead72d9f
Patch-mainline: v5.17-rc1
References: CVE-2021-44879 bsc#1195987
As report by Wenqing Liu in bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=215231
- Overview
kernel NULL pointer dereference triggered in folio_mark_dirty() when mount and operate on a crafted f2fs image
- Reproduce
tested on kernel 5.16-rc3, 5.15.X under root
1. mkdir mnt
2. mount -t f2fs tmp1.img mnt
3. touch tmp
4. cp tmp mnt
F2FS-fs (loop0): sanity_check_inode: inode (ino=49) extent info [5942, 4294180864, 4] is incorrect, run fsck to fix
F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=31340049, run fsck to fix.
Bug: kernel NULL pointer dereference, address: 0000000000000000 folio_mark_dirty+0x33/0x50 move_data_page+0x2dd/0x460 [f2fs] do_garbage_collect+0xc18/0x16a0 [f2fs] f2fs_gc+0x1d3/0xd90 [f2fs] f2fs_balance_fs+0x13a/0x570 [f2fs] f2fs_create+0x285/0x840 [f2fs] path_openat+0xe6d/0x1040 do_filp_open+0xc5/0x140 do_sys_openat2+0x23a/0x310 do_sys_open+0x57/0x80
The root cause is for special file: e.g. character, block, fifo or socket file,
f2fs doesn't assign address space operations pointer array for mapping->a_ops field,
so, in a fuzzed image, SSA table indicates a data block belong to special file, when
f2fs tries to migrate that block, it causes NULL pointer access once move_data_page()
calls a_ops->set_dirty_page().
Cc: stable@vger.kernel.org
Reported-by: Wenqing Liu <wenqingliu0120@gmail.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
fs/f2fs/gc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -809,7 +809,8 @@ next_step:
if (phase == 3) {
inode = f2fs_iget(sb, dni.ino);
- if (IS_ERR(inode) || is_bad_inode(inode))
+ if (IS_ERR(inode) || is_bad_inode(inode) ||
+ special_file(inode->i_mode))
continue;
/* if encrypted inode, let's go phase 3 */