169 lines
6.6 KiB
Diff
169 lines
6.6 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Jon DeVree <nuxi@vault24.org>
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Date: Tue, 17 Oct 2023 23:03:47 -0400
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Subject: [PATCH] fs/xfs: Fix XFS directory extent parsing
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The XFS directory entry parsing code has never been completely correct
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for extent based directories. The parser correctly handles the case
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where the directory is contained in a single extent, but then mistakenly
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assumes the data blocks for the multiple extent case are each identical
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to the single extent case. The difference in the format of the data
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blocks between the two cases is tiny enough that its gone unnoticed for
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a very long time.
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A recent change introduced some additional bounds checking into the XFS
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parser. Like GRUB's existing parser, it is correct for the single extent
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case but incorrect for the multiple extent case. When parsing a directory
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with multiple extents, this new bounds checking is sometimes (but not
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always) tripped and triggers an "invalid XFS directory entry" error. This
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probably would have continued to go unnoticed but the /boot/grub/<arch>
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directory is large enough that it often has multiple extents.
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The difference between the two cases is that when there are multiple
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extents, the data blocks do not contain a trailer nor do they contain
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any leaf information. That information is stored in a separate set of
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extents dedicated to just the leaf information. These extents come after
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the directory entry extents and are not included in the inode size. So
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the existing parser already ignores the leaf extents.
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The only reason to read the trailer/leaf information at all is so that
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the parser can avoid misinterpreting that data as directory entries. So
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this updates the parser as follows:
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For the single extent case the parser doesn't change much:
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1. Read the size of the leaf information from the trailer
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2. Set the end pointer for the parser to the start of the leaf
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information. (The previous bounds checking set the end pointer to the
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start of the trailer, so this is actually a small improvement.)
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3. Set the entries variable to the expected number of directory entries.
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For the multiple extent case:
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1. Set the end pointer to the end of the block.
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2. Do not set up the entries variable. Figuring out how many entries are
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in each individual block is complex and does not seem worth it when
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it appears to be safe to just iterate over the entire block.
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The bounds check itself was also dependent upon the faulty XFS parser
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because it accidentally used "filename + length - 1". Presumably this
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was able to pass the fuzzer because in the old parser there was always
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8 bytes of slack space between the tail pointer and the actual end of
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the block. Since this is no longer the case the bounds check needs to be
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updated to "filename + length + 1" in order to prevent a regression in
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the handling of corrupt fliesystems.
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Notes:
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* When there is only one extent there will only ever be one block. If
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more than one block is required then XFS will always switch to holding
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leaf information in a separate extent.
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* B-tree based directories seems to be parsed properly by the same code
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that handles multiple extents. This is unlikely to ever occur within
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/boot though because its only used when there are an extremely large
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number of directory entries.
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Fixes: ef7850c75 (fs/xfs: Fix issues found while fuzzing the XFS filesystem)
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Fixes: b2499b29c (Adds support for the XFS filesystem.)
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Fixes: https://savannah.gnu.org/bugs/?64376
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Signed-off-by: Jon DeVree <nuxi@vault24.org>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Tested-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
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Tested-by: Marta Lewandowska <mlewando@redhat.com>
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---
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grub-core/fs/xfs.c | 52 ++++++++++++++++++++++++++++++++++++++--------------
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1 file changed, 38 insertions(+), 14 deletions(-)
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diff --git a/grub-core/fs/xfs.c b/grub-core/fs/xfs.c
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index ebf962793fa7..18edfcff486c 100644
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--- a/grub-core/fs/xfs.c
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+++ b/grub-core/fs/xfs.c
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@@ -223,6 +223,12 @@ struct grub_xfs_inode
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/* Size of struct grub_xfs_inode v2, up to unused4 member included. */
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#define XFS_V2_INODE_SIZE (XFS_V3_INODE_SIZE - 76)
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+struct grub_xfs_dir_leaf_entry
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+{
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+ grub_uint32_t hashval;
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+ grub_uint32_t address;
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+} GRUB_PACKED;
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+
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struct grub_xfs_dirblock_tail
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{
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grub_uint32_t leaf_count;
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@@ -874,9 +880,8 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
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{
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struct grub_xfs_dir2_entry *direntry =
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grub_xfs_first_de(dir->data, dirblock);
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- int entries;
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- struct grub_xfs_dirblock_tail *tail =
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- grub_xfs_dir_tail(dir->data, dirblock);
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+ int entries = -1;
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+ char *end = dirblock + dirblk_size;
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numread = grub_xfs_read_file (dir, 0, 0,
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blk << dirblk_log2,
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@@ -887,14 +892,27 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
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return 0;
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}
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- entries = (grub_be_to_cpu32 (tail->leaf_count)
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- - grub_be_to_cpu32 (tail->leaf_stale));
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+ /*
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+ * Leaf and tail information are only in the data block if the number
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+ * of extents is 1.
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+ */
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+ if (dir->inode.nextents == grub_cpu_to_be32_compile_time (1))
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+ {
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+ struct grub_xfs_dirblock_tail *tail = grub_xfs_dir_tail (dir->data, dirblock);
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- if (!entries)
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- continue;
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+ end = (char *) tail;
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+
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+ /* Subtract the space used by leaf nodes. */
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+ end -= grub_be_to_cpu32 (tail->leaf_count) * sizeof (struct grub_xfs_dir_leaf_entry);
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+
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+ entries = grub_be_to_cpu32 (tail->leaf_count) - grub_be_to_cpu32 (tail->leaf_stale);
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+
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+ if (!entries)
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+ continue;
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+ }
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/* Iterate over all entries within this block. */
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- while ((char *)direntry < (char *)tail)
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+ while ((char *) direntry < (char *) end)
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{
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grub_uint8_t *freetag;
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char *filename;
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@@ -914,7 +932,7 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
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}
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filename = (char *)(direntry + 1);
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- if (filename + direntry->len - 1 > (char *) tail)
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+ if (filename + direntry->len + 1 > (char *) end)
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return grub_error (GRUB_ERR_BAD_FS, "invalid XFS directory entry");
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/* The byte after the filename is for the filetype, padding, or
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@@ -928,11 +946,17 @@ grub_xfs_iterate_dir (grub_fshelp_node_t dir,
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return 1;
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}
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- /* Check if last direntry in this block is
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- reached. */
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- entries--;
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- if (!entries)
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- break;
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+ /*
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+ * The expected number of directory entries is only tracked for the
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+ * single extent case.
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+ */
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+ if (dir->inode.nextents == grub_cpu_to_be32_compile_time (1))
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+ {
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+ /* Check if last direntry in this block is reached. */
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+ entries--;
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+ if (!entries)
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+ break;
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+ }
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/* Select the next directory entry. */
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direntry = grub_xfs_next_de(dir->data, direntry);
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