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squashfs: more metadata hardening

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The squashfs fragment reading code doesn't actually verify that the
fragment is inside the fragment table.  The end result _is_ verified to
be inside the image when actually reading the fragment data, but before
that is done, we may end up taking a page fault because the fragment
table itself might not even exist.

Another report from Anatoly and his endless squashfs image fuzzing.

Reported-by: Анатолий Тросиненко <anatoly.trosinenko@gmail.com>
Acked-by:: Phillip Lougher <phillip.lougher@gmail.com>,
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2018-08-02 08:43:35 -07:00
parent 6b47037682
commit 71755ee535
3 changed files with 13 additions and 6 deletions
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13
fs/squashfs/fragment.c
View file

@ -49,11 +49,16 @@ int squashfs_frag_lookup(struct super_block *sb, unsigned int fragment,
u64 *fragment_block)
{
struct squashfs_sb_info *msblk = sb->s_fs_info;
int block = SQUASHFS_FRAGMENT_INDEX(fragment);
int offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
u64 start_block = le64_to_cpu(msblk->fragment_index[block]);
int block, offset, size;
struct squashfs_fragment_entry fragment_entry;
int size;
u64 start_block;
if (fragment >= msblk->fragments)
return -EIO;
block = SQUASHFS_FRAGMENT_INDEX(fragment);
offset = SQUASHFS_FRAGMENT_INDEX_OFFSET(fragment);
start_block = le64_to_cpu(msblk->fragment_index[block]);
size = squashfs_read_metadata(sb, &fragment_entry, &start_block,
&offset, sizeof(fragment_entry));

1
fs/squashfs/squashfs_fs_sb.h
View file

@ -75,6 +75,7 @@ struct squashfs_sb_info {
unsigned short block_log;
long long bytes_used;
unsigned int inodes;
unsigned int fragments;
int xattr_ids;
};
#endif

5
fs/squashfs/super.c
View file

@ -175,6 +175,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
msblk->inode_table = le64_to_cpu(sblk->inode_table_start);
msblk->directory_table = le64_to_cpu(sblk->directory_table_start);
msblk->inodes = le32_to_cpu(sblk->inodes);
msblk->fragments = le32_to_cpu(sblk->fragments);
flags = le16_to_cpu(sblk->flags);
TRACE("Found valid superblock on %pg\n", sb->s_bdev);
@ -185,7 +186,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
TRACE("Filesystem size %lld bytes\n", msblk->bytes_used);
TRACE("Block size %d\n", msblk->block_size);
TRACE("Number of inodes %d\n", msblk->inodes);
TRACE("Number of fragments %d\n", le32_to_cpu(sblk->fragments));
TRACE("Number of fragments %d\n", msblk->fragments);
TRACE("Number of ids %d\n", le16_to_cpu(sblk->no_ids));
TRACE("sblk->inode_table_start %llx\n", msblk->inode_table);
TRACE("sblk->directory_table_start %llx\n", msblk->directory_table);
@ -272,7 +273,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
sb->s_export_op = &squashfs_export_ops;
handle_fragments:
fragments = le32_to_cpu(sblk->fragments);
fragments = msblk->fragments;
if (fragments == 0)
goto check_directory_table;