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squashfs: add more sanity checks in xattr id lookup 

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>
This commit is contained in:
Phillip Lougher 2021-02-09 13:42:00 -08:00 committed by Linus Torvalds
parent eabac19e40
commit 506220d2ba
1 changed files with 57 additions and 9 deletions
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66
fs/squashfs/xattr_id.c
View File

@ -31,10 +31,15 @@ int squashfs_xattr_lookup(struct super_block *sb, unsigned int index,
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)
@ -50,13 +55,17 @@ int squashfs_xattr_lookup(struct super_block *sb, unsigned int index,
/*
* 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;
@ -70,13 +79,52 @@ __le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 start,
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;
TRACE("In read_xattr_index_table, length %d\n", len);
/* 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]);
return squashfs_read_table(sb, start + sizeof(*id_table), len);
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);
}
if (*xattr_table_start >= le64_to_cpu(table[0])) {
kfree(table);
return ERR_PTR(-EINVAL);
}
return table;
}