[PATCH] f2fs: fix to avoid out-of-bounds access in f2fs_truncate_inode_blocks()

[Chao Yu <chao@kernel.org>]

syzbot reports an UBSAN issue as below:

------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in fs/f2fs/node.h:381:10
index 18446744073709550692 is out of range for type '__le32[5]' (aka 'unsigned int[5]')
CPU: 0 UID: 0 PID: 5318 Comm: syz.0.0 Not tainted 6.14.0-rc3-syzkaller-00060-g6537cfb395f3 #0
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:231 [inline]
 __ubsan_handle_out_of_bounds+0x121/0x150 lib/ubsan.c:429
 get_nid fs/f2fs/node.h:381 [inline]
 f2fs_truncate_inode_blocks+0xa5e/0xf60 fs/f2fs/node.c:1181
 f2fs_do_truncate_blocks+0x782/0x1030 fs/f2fs/file.c:808
 f2fs_truncate_blocks+0x10d/0x300 fs/f2fs/file.c:836
 f2fs_truncate+0x417/0x720 fs/f2fs/file.c:886
 f2fs_file_write_iter+0x1bdb/0x2550 fs/f2fs/file.c:5093
 aio_write+0x56b/0x7c0 fs/aio.c:1633
 io_submit_one+0x8a7/0x18a0 fs/aio.c:2052
 __do_sys_io_submit fs/aio.c:2111 [inline]
 __se_sys_io_submit+0x171/0x2e0 fs/aio.c:2081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f238798cde9

index 18446744073709550692 (decimal, unsigned long long)
= 0xfffffffffffffc64 (hexadecimal, unsigned long long)
= -924 (decimal, long long)

In f2fs_truncate_inode_blocks(), UBSAN detects that get_nid() tries to
access .i_nid[-924], it means both offset[0] and level should zero.

The possible case should be in f2fs_do_truncate_blocks(), we try to
truncate inode size to zero, however, dn.ofs_in_node is zero and
dn.node_page is not an inode page, so it fails to truncate inode page,
and then pass zeroed free_from to f2fs_truncate_inode_blocks(), result
in this issue.

	if (dn.ofs_in_node || IS_INODE(dn.node_page)) {
		f2fs_truncate_data_blocks_range(&dn, count);
		free_from += count;
	}

I guess the reason why dn.node_page is not an inode page could be: there
are multiple nat entries share the same node block address, once the node
block address was reused, f2fs_get_node_page() may load a non-inode block.

Let's add a sanity check for such condition to avoid out-of-bounds access
issue.

Reported-by: syzbot+6653f10281a1badc749e@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/66fdcdf3.050a0220.40bef.0025.GAE@google.com
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/node.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index e1ed7ccfb690..36614a1c2590 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -1135,7 +1135,14 @@ int f2fs_truncate_inode_blocks(struct inode *inode, pgoff_t from)
 	trace_f2fs_truncate_inode_blocks_enter(inode, from);
 
 	level = get_node_path(inode, from, offset, noffset);
-	if (level < 0) {
+	if (level <= 0) {
+		if (!level) {
+			level = -EFSCORRUPTED;
+			f2fs_err(sbi, "%s: inode ino=%lx has corrupted node block, from:%lu addrs:%u",
+					__func__, inode->i_ino,
+					from, ADDRS_PER_INODE(inode));
+			set_sbi_flag(sbi, SBI_NEED_FSCK);
+		}
 		trace_f2fs_truncate_inode_blocks_exit(inode, level);
 		return level;
 	}
-- 
2.48.1