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fs/xfs: Handle non-continuous data blocks in directory extents

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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 <nuxi@vault24.org>
Reviewed-By: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Jon DeVree 2024-02-11 10:34:58 -05:00 committed by Daniel Kiper
parent 04d2a50f31
commit 68dd65cfda
1 changed files with 10 additions and 0 deletions
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10
grub-core/fs/xfs.c
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@ -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 *)(void *) dirblock;
if (!magic)
continue;
/*
* Leaf and tail information are only in the data block if the number
* of extents is 1.