Re: [PATCH] fs/xfs: Avoid unreadble filesystem if V4 superblock

[Daniel Kiper]

On Wed, Aug 25, 2021 at 03:31:52PM +0200, Erwan Velu wrote:
> Commit 8b1e5d1936fffc490510e85c95f93248453586c1 introduced the support
> of bigtime by adding the some features in inodes V3.
>
> This change extended grub_xfs_inode struct by 76 bytes but also changed the
> computation of XFS_V3_INODE_SIZE & XFS_V2_INODE_SIZE.
>
> Prior this commit, XFS_V2_INODE_SIZE was 100 bytes, after the commit it's 84 
> bytes.
> XFS_V2_INODE_SIZE becomes 16 bytes too small.
>
> As a result, the data structure aren't properly aligned and generates
> "attempt to read or write outside of partition" errors when trying to
> read the filesystem.
>
>                              GNU GRUB  version 2.11
>       ....
>       grub> set debug=efi,gpt,xfs
>       grub> insmod part_gpt
>       grub> ls (hd0,gpt1)/
>       partmap/gpt.c:93: Read a valid GPT header
>       partmap/gpt.c:115: GPT entry 0: start=4096, length=1953125
>       fs/xfs.c:931: Reading sb
>       fs/xfs.c:270: Validating superblock
>       fs/xfs.c:295: XFS v4 superblock detected
>       fs/xfs.c:962: Reading root ino 128
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:515: Reading inode (739521961424144223) - 344365866970255880, 
> 3840
>       error: attempt to read or write outside of partition.
>
> This commit change the XFS_V2_INODE_SIZE computation by substracting 76
> instead of 92 from the actual size of grub_xfs_inode.
> This 76 value is coming from the added :
>       20 uint8   unused5
>        1 uint64  flags2
>         48 uint8   unused6
>
> This patch explicit the split between the v2 and v3 parts of structure.
> The unused4 is still ending to the v2 structures and the v3 starts at unused5.
> This will avoid future corruption of v2 or v3.
>
> The XFS_V2_INODE_SIZE is returning to its expected size and the
> filesystem is back to a readable state.
>
>                       GNU GRUB  version 2.11
>       ....
>       grub> set debug=efi,gpt,xfs
>       grub> insmod part_gpt
>       grub> ls (hd0,gpt1)/
>       partmap/gpt.c:93: Read a valid GPT header
>       partmap/gpt.c:115: GPT entry 0: start=4096, length=1953125
>       fs/xfs.c:931: Reading sb
>       fs/xfs.c:270: Validating superblock
>       fs/xfs.c:295: XFS v4 superblock detected
>       fs/xfs.c:962: Reading root ino 128
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:931: Reading sb
>       fs/xfs.c:270: Validating superblock
>       fs/xfs.c:295: XFS v4 superblock detected
>       fs/xfs.c:962: Reading root ino 128
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:515: Reading inode (128) - 64, 0
>       fs/xfs.c:515: Reading inode (131) - 64, 768
>       efi/ fs/xfs.c:515: Reading inode (3145856) - 1464904, 0
>       grub2/ fs/xfs.c:515: Reading inode (132) - 64, 1024
>       grub/ fs/xfs.c:515: Reading inode (139) - 64, 2816
>       grub>
>
> Signed-off-by: Erwan Velu <e.velu@criteo.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel