From 68dd65cfdaad08b1f8ec01b84949b0bf88bc0d8c Mon Sep 17 00:00:00 2001
From: Jon DeVree <[email protected]>
Date: Sun, 11 Feb 2024 10:34:58 -0500
Subject: [PATCH 0990/1000] fs/xfs: Handle non-continuous data blocks in
 directory extents

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 (fs/xfs: Fix XFS directory extent parsing)
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 <[email protected]>
Reviewed-By: Vladimir Serbinenko <[email protected]>
Reviewed-by: Daniel Kiper <[email protected]>
---
 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 1ce5fa4..2a22e26 100644
--- a/grub-core/fs/xfs.c
+++ b/grub-core/fs/xfs.c
@@ -904,6 +904,7 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
 
 	    int entries = -1;
 	    char *end = dirblock + dirblk_size;
+            grub_uint32_t magic;
 
 	    numread = grub_xfs_read_file (dir, 0, 0,
 					  blk << dirblk_log2,
@@ -914,6 +915,15 @@ 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 *)(void *) dirblock;
+            if (!magic)
+              continue;
+
 	    /*
 	     * Leaf and tail information are only in the data block if the number
 	     * of extents is 1.
-- 
2.33.0