[PATCH 3.18 65/85] squashfs: be more careful about metadata corruption

Greg Kroah-Hartman
2018-08-07T18:59:20Z

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 01cfb7937a9af2abb1136c7e89fbf3fd92952956 upstream.

Anatoly Trosinenko reports that a corrupted squashfs image can cause a
kernel oops. It turns out that squashfs can end up being confused about
negative fragment lengths.

The regular squashfs_read_data() does check for negative lengths, but
squashfs_read_metadata() did not, and the fragment size code just
blindly trusted the on-disk value. Fix both the fragment parsing and
the metadata reading code.

Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/squashfs/cache.c | 3 +++
fs/squashfs/file.c | 8 ++++++--
fs/squashfs/fragment.c | 4 +---
fs/squashfs/squashfs_fs.h | 6 ++++++
4 files changed, 16 insertions(+), 5 deletions(-)

--- a/fs/squashfs/cache.c
+++ b/fs/squashfs/cache.c
@@ -350,6 +350,9 @@ int squashfs_read_metadata(struct super_

TRACE("Entered squashfs_read_metadata [%llx:%x]\n", *block, *offset);

+ if (unlikely(length < 0))
+ return -EIO;
+
while (length) {
entry = squashfs_cache_get(sb, msblk->block_cache, *block, 0);
if (entry->error) {
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -194,7 +194,11 @@ static long long read_indexes(struct sup
}

for (i = 0; i < blocks; i++) {
- int size = le32_to_cpu(blist[i]);
+ int size = squashfs_block_size(blist[i]);
+ if (size < 0) {
+ err = size;
+ goto failure;
+ }
block += SQUASHFS_COMPRESSED_SIZE_BLOCK(size);
}
n -= blocks;
@@ -367,7 +371,7 @@ static int read_blocklist(struct inode *
sizeof(size));
if (res < 0)
return res;
- return le32_to_cpu(size);
+ return squashfs_block_size(size);
}

/* Copy data into page cache */
--- a/fs/squashfs/fragment.c
+++ b/fs/squashfs/fragment.c
@@ -61,9 +61,7 @@ int squashfs_frag_lookup(struct super_bl
return size;

*fragment_block = le64_to_cpu(fragment_entry.start_block);
- size = le32_to_cpu(fragment_entry.size);
-
- return size;
+ return squashfs_block_size(fragment_entry.size);
}

--- a/fs/squashfs/squashfs_fs.h
+++ b/fs/squashfs/squashfs_fs.h
@@ -129,6 +129,12 @@

#define SQUASHFS_COMPRESSED_BLOCK(B) (!((B) & SQUASHFS_COMPRESSED_BIT_BLOCK))

+static inline int squashfs_block_size(__le32 raw)
+{
+ u32 size = le32_to_cpu(raw);
+ return (size >> 25) ? -EIO : size;
+}
+
/*
* Inode number ops. Inodes consist of a compressed block number, and an
* uncompressed offset within that block