Squashfs: add sanity checks to id reading at mount time

Fsfuzzer generates corrupted filesystems which throw a warn_on in
kmalloc.  One of these is due to a corrupted superblock no_ids 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 id table
structures.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

4 files changed, 37 insertions, 6 deletions

diff --git a/fs/squashfs/id.c b/fs/squashfs/id.c
index 2fdac6703b48..499d08a1f34a 100644
--- a/fs/squashfs/id.c
+++ b/fs/squashfs/id.c
@@ -66,11 +66,37 @@ int squashfs_get_id(struct super_block *sb, unsigned int index,
  * Read uncompressed id lookup table indexes from disk into memory
  */
 __le64 *squashfs_read_id_index_table(struct super_block *sb,
-                        u64 id_table_start, unsigned short no_ids)
+                u64 id_table_start, u64 next_table, unsigned short no_ids)
 {
         unsigned int length = SQUASHFS_ID_BLOCK_BYTES(no_ids);
+        __le64 *table;
 
         TRACE("In read_id_index_table, length %d\n", length);
 
-        return squashfs_read_table(sb, id_table_start, length);
+        /* Sanity check values */
+
+        /* there should always be at least one id */
+        if (no_ids == 0)
+                return ERR_PTR(-EINVAL);
+
+        /*
+         * length bytes should not extend into the next table - this check
+         * also traps instances where id_table_start is incorrectly larger
+         * than the next table start
+         */
+        if (id_table_start + length > next_table)
+                return ERR_PTR(-EINVAL);
+
+        table = squashfs_read_table(sb, id_table_start, length);
+
+        /*
+         * table[0] points to the first id lookup table metadata block, this
+         * should be less than id_table_start
+         */
+        if (!IS_ERR(table) && table[0] >= id_table_start) {
+                kfree(table);
+                return ERR_PTR(-EINVAL);
+        }
+
+        return table;
 }
diff --git a/fs/squashfs/squashfs.h b/fs/squashfs/squashfs.h
index d622e849a451..0e3d220defd2 100644
--- a/fs/squashfs/squashfs.h
+++ b/fs/squashfs/squashfs.h
@@ -61,7 +61,7 @@ extern __le64 *squashfs_read_fragment_index_table(struct super_block *,
 
 /* id.c */
 extern int squashfs_get_id(struct super_block *, unsigned int, unsigned int *);
-extern __le64 *squashfs_read_id_index_table(struct super_block *, u64,
+extern __le64 *squashfs_read_id_index_table(struct super_block *, u64, u64,
                                 unsigned short);
 
 /* inode.c */
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 401cc8c7608f..8f5f2781a60e 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -83,7 +83,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
         long long root_inode;
         unsigned short flags;
         unsigned int fragments;
-        u64 lookup_table_start, xattr_id_table_start;
+        u64 lookup_table_start, xattr_id_table_start, next_table;
         int err;
 
         TRACE("Entered squashfs_fill_superblock\n");
@@ -217,8 +217,10 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
         /* Handle xattrs */
         sb->s_xattr = squashfs_xattr_handlers;
         xattr_id_table_start = le64_to_cpu(sblk->xattr_id_table_start);
-        if (xattr_id_table_start == SQUASHFS_INVALID_BLK)
+        if (xattr_id_table_start == SQUASHFS_INVALID_BLK) {
+                next_table = msblk->bytes_used;
                 goto allocate_id_index_table;
+        }
 
         /* Allocate and read xattr id lookup table */
         msblk->xattr_id_table = squashfs_read_xattr_id_table(sb,
@@ -230,11 +232,13 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
                 if (err != -ENOTSUPP)
                         goto failed_mount;
         }
+        next_table = msblk->xattr_table;
 
 allocate_id_index_table:
         /* Allocate and read id index table */
         msblk->id_table = squashfs_read_id_index_table(sb,
-                le64_to_cpu(sblk->id_table_start), le16_to_cpu(sblk->no_ids));
+                le64_to_cpu(sblk->id_table_start), next_table,
+                le16_to_cpu(sblk->no_ids));
         if (IS_ERR(msblk->id_table)) {
                 ERROR("unable to read id index table\n");
                 err = PTR_ERR(msblk->id_table);
diff --git a/fs/squashfs/xattr.h b/fs/squashfs/xattr.h
index b634efce4bde..9b3dd6c4c1fe 100644
--- a/fs/squashfs/xattr.h
+++ b/fs/squashfs/xattr.h
@@ -31,6 +31,7 @@ static inline __le64 *squashfs_read_xattr_id_table(struct super_block *sb,
                 u64 start, u64 *xattr_table_start, int *xattr_ids)
 {
         ERROR("Xattrs in filesystem, these will be ignored\n");
+        *xattr_table_start = start;
         return ERR_PTR(-ENOTSUPP);
 }