f2fs: fix to avoid updating compression context during writeback

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to avoid updating compression context during writeback

Bai, Shuangpeng <[email protected]> reported a bug as below:

Oops: divide error: 0000 [#1] SMP KASAN PTI

CPU: 0 UID: 0 PID: 11441 Comm: syz.0.46 Not tainted 6.17.0 #1 PREEMPT(full)

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014

RIP: 0010:f2fs_all_cluster_page_ready+0x106/0x550 fs/f2fs/compress.c:857

Call Trace:

<TASK>

f2fs_write_cache_pages fs/f2fs/data.c:3078 [inline]

__f2fs_write_data_pages fs/f2fs/data.c:3290 [inline]

f2fs_write_data_pages+0x1c19/0x3600 fs/f2fs/data.c:3317

do_writepages+0x38e/0x640 mm/page-writeback.c:2634

filemap_fdatawrite_wbc mm/filemap.c:386 [inline]

__filemap_fdatawrite_range mm/filemap.c:419 [inline]

file_write_and_wait_range+0x2ba/0x3e0 mm/filemap.c:794

f2fs_do_sync_file+0x6e6/0x1b00 fs/f2fs/file.c:294

generic_write_sync include/linux/fs.h:3043 [inline]

f2fs_file_write_iter+0x76e/0x2700 fs/f2fs/file.c:5259

new_sync_write fs/read_write.c:593 [inline]

vfs_write+0x7e9/0xe00 fs/read_write.c:686

ksys_write+0x19d/0x2d0 fs/read_write.c:738

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0xf7/0x470 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

The bug was triggered w/ below race condition:

fsync setattr ioctl

- f2fs_do_sync_file

- file_write_and_wait_range

- f2fs_write_cache_pages

: inode is non-compressed

: cc.cluster_size =

F2FS_I(inode)->i_cluster_size = 0

- tag_pages_for_writeback

- f2fs_setattr

- truncate_setsize

- f2fs_truncate

- f2fs_fileattr_set

- f2fs_setflags_common

- set_compress_context

: F2FS_I(inode)->i_cluster_size = 4

: set_inode_flag(inode, FI_COMPRESSED_FILE)

- f2fs_compressed_file

: return true

- f2fs_all_cluster_page_ready

: "pgidx % cc->cluster_size" trigger dividing 0 issue

Let's change as below to fix this issue:

- introduce a new atomic type variable .writeback in structure f2fs_inode_info

to track the number of threads which calling f2fs_write_cache_pages().

- use .i_sem lock to protect .writeback update.

- check .writeback before update compression context in f2fs_setflags_common()

to avoid race w/ ->writepages.