Re: [PATCH -next RFC] f2fs: fix null-ptr-deref in f2fs_get_dnode_of_data

[Chao Yu]

On 2022/7/18 19:36, Ye Bin wrote:
> There is issue as follows when test f2fs atomic write:
> F2FS-fs (loop0): Can't find valid F2FS filesystem in 2th superblock
> F2FS-fs (loop0): invalid crc_offset: 0
> F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=1, run fsck to fix.
> F2FS-fs (loop0): f2fs_check_nid_range: out-of-range nid=2, run fsck to fix.
> ==================================================================
> BUG: KASAN: null-ptr-deref in f2fs_get_dnode_of_data+0xac/0x16d0
> Read of size 8 at addr 0000000000000028 by task rep/1990
>
> CPU: 4 PID: 1990 Comm: rep Not tainted 5.19.0-rc6-next-20220715 #266
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0x6e/0x91
>   print_report.cold+0x49a/0x6bb
>   kasan_report+0xa8/0x130
>   f2fs_get_dnode_of_data+0xac/0x16d0
>   f2fs_do_write_data_page+0x2a5/0x1030
>   move_data_page+0x3c5/0xdf0
>   do_garbage_collect+0x2015/0x36c0
>   f2fs_gc+0x554/0x1d30
>   f2fs_balance_fs+0x7f5/0xda0
>   f2fs_write_single_data_page+0xb66/0xdc0
>   f2fs_write_cache_pages+0x716/0x1420
>   f2fs_write_data_pages+0x84f/0x9a0
>   do_writepages+0x130/0x3a0
>   filemap_fdatawrite_wbc+0x87/0xa0
>   file_write_and_wait_range+0x157/0x1c0
>   f2fs_do_sync_file+0x206/0x12d0
>   f2fs_sync_file+0x99/0xc0
>   vfs_fsync_range+0x75/0x140
>   f2fs_file_write_iter+0xd7b/0x1850
>   vfs_write+0x645/0x780
>   ksys_write+0xf1/0x1e0
>   do_syscall_64+0x3b/0x90
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>
> As 3db1de0e582c commit changed atomic write way which new a cow_inode for
> atomic write file, and also mark cow_inode as FI_ATOMIC_FILE.
> When f2fs_do_write_data_page write cow_inode will use cow_inode's cow_inode
> which is NULL. Then will trigger null-ptr-deref.
> To solve above issue, don't mark cow_inode as FI_ATOMIC_FILE.
>
> Fiexes: 3db1de0e582c("f2fs: change the current atomic write way")
> Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> ---
>   fs/f2fs/file.c | 1 -
>   1 file changed, 1 deletion(-)
>
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 466eb00aa516..735802b6b754 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -2062,7 +2062,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>   
>   	set_inode_flag(inode, FI_ATOMIC_FILE);
> -	set_inode_flag(fi->cow_inode, FI_ATOMIC_FILE);

It needs to remove clear_inode_flag(fi->cow_inode, FI_ATOMIC_FILE) in
f2fs_abort_atomic_write()?

To Daeho, could you please review this patch? IIUC, cow_inode doesn't
need to be set as atomic file?

Thanks,

>   	clear_inode_flag(fi->cow_inode, FI_INLINE_DATA);
>   	f2fs_up_write(&fi->i_gc_rwsem[WRITE]);
>