Squashfs: handle corruption of directory structure

Handle the rare case where a directory metadata block is uncompressed and
corrupted, leading to a kernel oops in directory scanning (memcpy).
Normally corruption is detected at the decompression stage and dealt with
then, however, this will not happen if:

- metadata isn't compressed (users can optionally request no metadata
  compression), or
- the compressed metadata block was larger than the original, in which
  case the uncompressed version was used, or
- the data was corrupt after decompression

This patch fixes this by adding some sanity checks against known maximum
values.

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

2 files changed, 21 insertions, 0 deletions

diff --git a/fs/squashfs/dir.c b/fs/squashfs/dir.c
index 0dc340aa2be9..3f79cd1d0c19 100644
--- a/fs/squashfs/dir.c
+++ b/fs/squashfs/dir.c
@@ -172,6 +172,11 @@ static int squashfs_readdir(struct file *file, void *dirent, filldir_t filldir)
                 length += sizeof(dirh);
 
                 dir_count = le32_to_cpu(dirh.count) + 1;
+
+                /* dir_count should never be larger than 256 */
+                if (dir_count > 256)
+                        goto failed_read;
+
                 while (dir_count--) {
                         /*
                          * Read directory entry.
@@ -183,6 +188,10 @@ static int squashfs_readdir(struct file *file, void *dirent, filldir_t filldir)
 
                         size = le16_to_cpu(dire->size) + 1;
 
+                        /* size should never be larger than SQUASHFS_NAME_LEN */
+                        if (size > SQUASHFS_NAME_LEN)
+                                goto failed_read;
+
                         err = squashfs_read_metadata(inode->i_sb, dire->name,
                                         &block, &offset, size);
                         if (err < 0)
diff --git a/fs/squashfs/namei.c b/fs/squashfs/namei.c
index 7a9464d08cf6..5d922a6701ab 100644
--- a/fs/squashfs/namei.c
+++ b/fs/squashfs/namei.c
@@ -176,6 +176,11 @@ static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
                 length += sizeof(dirh);
 
                 dir_count = le32_to_cpu(dirh.count) + 1;
+
+                /* dir_count should never be larger than 256 */
+                if (dir_count > 256)
+                        goto data_error;
+
                 while (dir_count--) {
                         /*
                          * Read directory entry.
@@ -187,6 +192,10 @@ static struct dentry *squashfs_lookup(struct inode *dir, struct dentry *dentry,
 
                         size = le16_to_cpu(dire->size) + 1;
 
+                        /* size should never be larger than SQUASHFS_NAME_LEN */
+                        if (size > SQUASHFS_NAME_LEN)
+                                goto data_error;
+
                         err = squashfs_read_metadata(dir->i_sb, dire->name,
                                         &block, &offset, size);
                         if (err < 0)
@@ -228,6 +237,9 @@ exit_lookup:
         d_add(dentry, inode);
         return ERR_PTR(0);
 
+data_error:
+        err = -EIO;
+
 read_failure:
         ERROR("Unable to read directory block [%llx:%x]\n",
                 squashfs_i(dir)->start + msblk->directory_table,