[PATCH 4.9 18/49] squashfs: add more sanity checks in xattr id lookup

Greg Kroah-Hartman
2021-02-22T13:55:53Z

From: Phillip Lougher <phillip@squashfs.org.uk>

commit 506220d2ba21791314af569211ffd8870b8208fa upstream.

Sysbot has reported a warning where a kmalloc() attempt exceeds the
maximum limit. This has been identified as corruption of the xattr_ids
count when reading the xattr id lookup table.

This patch adds a number of additional sanity checks to detect this
corruption and others.

1. It checks for a corrupted xattr index read from the inode. This could
be because the metadata block is uncompressed, or because the
"compression" bit has been corrupted (turning a compressed block
into an uncompressed block). This would cause an out of bounds read.

2. It checks against corruption of the xattr_ids count. This can either
lead to the above kmalloc failure, or a smaller than expected
table to be read.

3. It checks the contents of the index table for corruption.

[phillip@squashfs.org.uk: fix checkpatch issue]
Link: https://lkml.kernel.org/r/270245655.754655.1612770082682@webmail.123-reg.co.uk

Link: https://lkml.kernel.org/r/20210204130249.4495-5-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: syzbot+2ccea6339d368360800d@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/squashfs/xattr_id.c | 66 ++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 57 insertions(+), 9 deletions(-)

--- a/fs/squashfs/xattr_id.c
+++ b/fs/squashfs/xattr_id.c
@@ -44,10 +44,15 @@ int squashfs_xattr_lookup(struct super_b
struct squashfs_sb_info *msblk = sb->s_fs_info;
int block = SQUASHFS_XATTR_BLOCK(index);
int offset = SQUASHFS_XATTR_BLOCK_OFFSET(index);
- u64 start_block = le64_to_cpu(msblk->xattr_id_table[block]);
+ u64 start_block;
struct squashfs_xattr_id id;
int err;

+ if (index >= msblk->xattr_ids)
+ return -EINVAL;
+
+ start_block = le64_to_cpu(msblk->xattr_id_table[block]);
+
err = squashfs_read_metadata(sb, &id, &start_block, &offset,
sizeof(id));
if (err < 0)
@@ -63,13 +68,17 @@ int squashfs_xattr_lookup(struct super_b
/*
* Read uncompressed xattr id lookup table indexes from disk into memory
*/
-__le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start,
+__le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 table_start,
u64 *xattr_table_start, int *xattr_ids)
{
- unsigned int len;
+ struct squashfs_sb_info *msblk = sb->s_fs_info;
+ unsigned int len, indexes;
struct squashfs_xattr_id_table *id_table;
+ __le64 *table;
+ u64 start, end;
+ int n;

- id_table = squashfs_read_table(sb, start, sizeof(*id_table));
+ id_table = squashfs_read_table(sb, table_start, sizeof(*id_table));
if (IS_ERR(id_table))
return (__le64 *) id_table;

@@ -83,13 +92,52 @@ __le64 *squashfs_read_xattr_id_table(str
if (*xattr_ids == 0)
return ERR_PTR(-EINVAL);

- /* xattr_table should be less than start */
- if (*xattr_table_start >= start)
+ len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids);
+ indexes = SQUASHFS_XATTR_BLOCKS(*xattr_ids);
+
+ /*
+ * The computed size of the index table (len bytes) should exactly
+ * match the table start and end points
+ */
+ start = table_start + sizeof(*id_table);
+ end = msblk->bytes_used;
+
+ if (len != (end - start))
return ERR_PTR(-EINVAL);

- len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids);
+ table = squashfs_read_table(sb, start, len);
+ if (IS_ERR(table))
+ return table;
+
+ /* table[0], table[1], ... table[indexes - 1] store the locations
+ * of the compressed xattr id blocks. Each entry should be less than
+ * the next (i.e. table[0] < table[1]), and the difference between them
+ * should be SQUASHFS_METADATA_SIZE or less. table[indexes - 1]
+ * should be less than table_start, and again the difference
+ * shouls be SQUASHFS_METADATA_SIZE or less.
+ *
+ * Finally xattr_table_start should be less than table[0].
+ */
+ for (n = 0; n < (indexes - 1); n++) {
+ start = le64_to_cpu(table[n]);
+ end = le64_to_cpu(table[n + 1]);
+
+ if (start >= end || (end - start) > SQUASHFS_METADATA_SIZE) {
+ kfree(table);
+ return ERR_PTR(-EINVAL);
+ }
+ }
+
+ start = le64_to_cpu(table[indexes - 1]);
+ if (start >= table_start || (table_start - start) > SQUASHFS_METADATA_SIZE) {
+ kfree(table);
+ return ERR_PTR(-EINVAL);
+ }

- TRACE("In read_xattr_index_table, length %d\n", len);
+ if (*xattr_table_start >= le64_to_cpu(table[0])) {
+ kfree(table);
+ return ERR_PTR(-EINVAL);
+ }

- return squashfs_read_table(sb, start + sizeof(*id_table), len);
+ return table;
}