Re: [PATCH V0 RESEND] f2fs: fix error map extent flag while block not allocated

Chao Yu
2025-01-22T11:40:39Z

Hi Zhangqi,

On 1/13/25 13:57, chenzhangqi79@163.com wrote:
> From: Zhangqi Chen <chenzhangqi@xiaomi.com>
>
> In the function f2fs_fiemap, when returning the file
> map extent flag, the flag of the delayed allocation
> block is set to FIEMAP_EXTENT_UNWRITTEN . At the same
> time, the phy address of the file map extent reassigned
> to 0 because it is not a valid address.
>
> In this way, the file map extent with address 0 and
> FIEMAP_EXTENT_UNWRITTEN flag returned by ioctl, and
> may be used for writing by userspace programs, thereby
> destroying the superblock of the file system.

I agree with you.

FYI, there is a previous patch as below:

https://lore.kernel.org/linux-f2fs-devel/20230405144359.930253-1-chao@kernel.org/

It seems such change will fail some testcases of xfstest, have you check
this patch w/ 009, 092 and 094 in tests/generic/?

Thanks,

>
> As mentioned in /Documentation/filesystems/fiemap.txt,
> FIEMAP_EXTENT_UNWRITTEN should mean that the block has
> been allocated but not filled with data. However, the
> actual situation in f2fs is that there is no allocated
> block, so it should be changed to FIEMAP_EXTENT_UNKNOWN
> and FIEMAP_EXTENT_DELALLOC.
>
> Co-developed-by: Zhijun Li <lizhijun3@xiaomi.com>
> Signed-off-by: Zhijun Li <lizhijun3@xiaomi.com>
> Signed-off-by: Zhangqi Chen <chenzhangqi@xiaomi.com>
> ---
> fs/f2fs/data.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 2ec0cfb41260..a945d1f1d40c 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2023,7 +2023,7 @@ int f2fs_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> size += F2FS_BLKSIZE;
> }
> } else if (map.m_flags & F2FS_MAP_DELALLOC) {
> - flags = FIEMAP_EXTENT_UNWRITTEN;
> + flags = FIEMAP_EXTENT_UNKNOWN | FIEMAP_EXTENT_DELALLOC;
> }
>
> start_blk += F2FS_BYTES_TO_BLK(size);