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Subject[PATCH 5/7] Squashfs: add sanity checks to lookup table reading at mount time
Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc. One of these is due to a corrupted superblock inodes field.
Fix this by checking that the number of bytes to be read (and allocated)
does not extend into the next filesystem structure.

Also add a couple of other sanity checks of the mount-time lookup table
structures.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
---
fs/squashfs/export.c | 29 +++++++++++++++++++++++++++--
fs/squashfs/squashfs.h | 2 +-
fs/squashfs/super.c | 3 ++-
3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/fs/squashfs/export.c b/fs/squashfs/export.c
index cc6dd90..e54e4cb 100644
--- a/fs/squashfs/export.c
+++ b/fs/squashfs/export.c
@@ -121,13 +121,38 @@ static struct dentry *squashfs_get_parent(struct dentry *child)
* Read uncompressed inode lookup table indexes off disk into memory
*/
__le64 *squashfs_read_inode_lookup_table(struct super_block *sb,
- u64 lookup_table_start, unsigned int inodes)
+ u64 lookup_table_start, u64 next_table, unsigned int inodes)
{
unsigned int length = SQUASHFS_LOOKUP_BLOCK_BYTES(inodes);
+ __le64 *table;

TRACE("In read_inode_lookup_table, length %d\n", length);

- return squashfs_read_table(sb, lookup_table_start, length);
+ /* Sanity check values */
+
+ /* there should always be at least one inode */
+ if (inodes == 0)
+ return ERR_PTR(-EINVAL);
+
+ /* length bytes should not extend into the next table - this check
+ * also traps instances where lookup_table_start is incorrectly larger
+ * than the next table start
+ */
+ if (lookup_table_start + length > next_table)
+ return ERR_PTR(-EINVAL);
+
+ table = squashfs_read_table(sb, lookup_table_start, length);
+
+ /*
+ * table[0] points to the first inode lookup table metadata block,
+ * this should be less than lookup_table_start
+ */
+ if (table[0] >= lookup_table_start) {
+ kfree(table);
+ return ERR_PTR(-EINVAL);
+ }
+
+ return table;
}


diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index 0e3d220..3b705f1 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -51,7 +51,7 @@ extern const struct squashfs_decompressor *squashfs_lookup_decompressor(int);
extern void *squashfs_decompressor_init(struct super_block *, unsigned short);

/* export.c */
-extern __le64 *squashfs_read_inode_lookup_table(struct super_block *, u64,
+extern __le64 *squashfs_read_inode_lookup_table(struct super_block *, u64, u64,
unsigned int);

/* fragment.c */
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 8f5f278..80a7119 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -245,6 +245,7 @@ allocate_id_index_table:
msblk->id_table = NULL;
goto failed_mount;
}
+ next_table = msblk->id_table[0];

/* Handle inode lookup table */
lookup_table_start = le64_to_cpu(sblk->lookup_table_start);
@@ -253,7 +254,7 @@ allocate_id_index_table:

/* Allocate and read inode lookup table */
msblk->inode_lookup_table = squashfs_read_inode_lookup_table(sb,
- lookup_table_start, msblk->inodes);
+ lookup_table_start, next_table, msblk->inodes);
if (IS_ERR(msblk->inode_lookup_table)) {
ERROR("unable to read inode lookup table\n");
err = PTR_ERR(msblk->inode_lookup_table);
--
1.7.1


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