Re: [PATCH] fs/xfs: Handle non-continuous data blocks in directory extents

[Daniel Kiper]

Adding Marta, Nicolas, Sebastian and Vladimir...

Jon, thank you for the patch!

Marta, Nicolas and Sebastian, may I ask you to run tests with this fix?

Daniel

On Sun, Feb 11, 2024 at 10:34:58AM -0500, Jon DeVree wrote:
> The directory extent list does not have to be a continuous list of data
> blocks. When GRUB tries to read a non-existant member of the list,
> grub_xfs_read_file() will return a block of zero'ed memory. Checking for
> a zero'ed magic number is sufficient to skip this non-existant data
> block.
>
> Prior to commit 07318ee7e this was handled as a subtle side effect of
> reading the (non-existant) tail data structure. Since the block was
> zero'ed the computation of the number of directory entries in the block
> would return 0 as well.
>
> Fixes: 07318ee7e (fs/xfs: Fix XFS directory extent parsing)
> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2254370
> Signed-off-by: Jon DeVree <nuxi@vault24.org>
> ---
>  grub-core/fs/xfs.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/grub-core/fs/xfs.c b/grub-core/fs/xfs.c
> index bc2224dbb..a6cce9cfe 100644
> --- a/grub-core/fs/xfs.c
> +++ b/grub-core/fs/xfs.c
> @@ -902,6 +902,7 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
>                                       grub_xfs_first_de(dir->data, dirblock);
>           int entries = -1;
>           char *end = dirblock + dirblk_size;
> +         grub_uint32_t magic;
>
>           numread = grub_xfs_read_file (dir, 0, 0,
>                                         blk << dirblk_log2,
> @@ -912,6 +913,15 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
>               return 0;
>             }
>
> +         /*
> +          * If this data block isn't actually part of the extent list then
> +          * grub_xfs_read_file() returns a block of zeros. So if the magic 
> number
> +          * field is all zeros then this block should be skipped.
> +          */
> +         magic = *(grub_uint32_t *)dirblock;
> +         if (!magic)
> +           continue;
> +
>           /*
>            * Leaf and tail information are only in the data block if the 
> number
>            * of extents is 1.
> --
> 2.43.0