From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Erwan Velu <[email protected]>
Date: Wed, 25 Aug 2021 15:31:52 +0200
Subject: [PATCH] fs/xfs: Fix unreadable filesystem with v4 superblock

The commit 8b1e5d193 (fs/xfs: Add bigtime incompat feature support)
introduced the bigtime support by adding some features in v3 inodes.
This change extended grub_xfs_inode struct by 76 bytes but also changed
the computation of XFS_V2_INODE_SIZE and XFS_V3_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 structures aren't properly aligned and the GRUB
generates "attempt to read or write outside of partition" errors when
trying to read the XFS 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 subtracting 76
bytes instead of 92 bytes from the actual size of grub_xfs_inode struct.
This 76 bytes value comes from added members:
	20 grub_uint8_t   unused5
	 1 grub_uint64_t  flags2
        48 grub_uint8_t   unused6

This patch explicitly splits the v2 and v3 parts of the structure.
The unused4 is still ending of the v2 structures and the v3 starts
at unused5. Thanks to this we will avoid future corruptions of v2
or v3 inodes.

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>

Fixes: 8b1e5d193 (fs/xfs: Add bigtime incompat feature support)

Signed-off-by: Erwan Velu <[email protected]>
Tested-by: Carlos Maiolino <[email protected]>
Reviewed-by: Daniel Kiper <[email protected]>
(cherry picked from commit a4b495520e4dc41a896a8b916a64eda9970c50ea)
---
 grub-core/fs/xfs.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/grub-core/fs/xfs.c b/grub-core/fs/xfs.c
index 0f524c3a8a6..e3816d1ec4a 100644
--- a/grub-core/fs/xfs.c
+++ b/grub-core/fs/xfs.c
@@ -192,6 +192,11 @@ struct grub_xfs_time_legacy
   grub_uint32_t nanosec;
 } GRUB_PACKED;
 
+/*
+ * The struct grub_xfs_inode layout was taken from the
+ * struct xfs_dinode_core which is described here:
+ * https://mirrors.edge.kernel.org/pub/linux/utils/fs/xfs/docs/xfs_filesystem_structure.pdf
+ */
 struct grub_xfs_inode
 {
   grub_uint8_t magic[2];
@@ -208,14 +213,15 @@ struct grub_xfs_inode
   grub_uint32_t nextents;
   grub_uint16_t unused3;
   grub_uint8_t fork_offset;
-  grub_uint8_t unused4[37];
+  grub_uint8_t unused4[17]; /* Last member of inode v2. */
+  grub_uint8_t unused5[20]; /* First member of inode v3. */
   grub_uint64_t flags2;
-  grub_uint8_t unused5[48];
+  grub_uint8_t unused6[48]; /* Last member of inode v3. */
 } GRUB_PACKED;
 
 #define XFS_V3_INODE_SIZE	sizeof(struct grub_xfs_inode)
-/* Size of struct grub_xfs_inode until fork_offset (included). */
-#define XFS_V2_INODE_SIZE	(XFS_V3_INODE_SIZE - 92)
+/* Size of struct grub_xfs_inode v2, up to unused4 member included. */
+#define XFS_V2_INODE_SIZE	(XFS_V3_INODE_SIZE - 76)
 
 struct grub_xfs_dirblock_tail
 {