linux-kernel - [PATCH 1/3] f2fs: fix to do sanity check on inode type during garbage collection

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Message-Id: <20211206144421.3735-1-chao@kernel.org>
Date:   Mon,  6 Dec 2021 22:44:19 +0800
From:   Chao Yu <chao@...nel.org>
To:     jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao@...nel.org>,
        stable@...r.kernel.org, Wenqing Liu <wenqingliu0120@...il.com>
Subject: [PATCH 1/3] f2fs: fix to do sanity check on inode type during garbage collection

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@...r.kernel.org
Reported-by: Wenqing Liu <wenqingliu0120@...il.com>
Signed-off-by: Chao Yu <chao@...nel.org>
---
 fs/f2fs/gc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a946ce0ead34..e0bdc4361a9b 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1457,7 +1457,8 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 
 		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 (!down_write_trylock(
-- 
2.32.0