eCryptfs: NULL crypt_stat dereference during lookup

If ecryptfs_encrypted_view or ecryptfs_xattr_metadata were being
specified as mount options, a NULL pointer dereference of crypt_stat
was possible during lookup.

This patch moves the crypt_stat assignment into
ecryptfs_lookup_and_interpose_lower(), ensuring that crypt_stat
will not be NULL before we attempt to dereference it.

Thanks to Dan Carpenter and his static analysis tool, smatch, for
finding this bug.
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>
Acked-by: Dustin Kirkland <kirkland@canonical.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ecryptfs/crypto.c

@@ -2221,17 +2221,19 @@ int ecryptfs_decode_and_decrypt_filename(char **plaintext_name,
 					 struct dentry *ecryptfs_dir_dentry,
 					 const char *name, size_t name_size)
 {
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
+		&ecryptfs_superblock_to_private(
+			ecryptfs_dir_dentry->d_sb)->mount_crypt_stat;
 	char *decoded_name;
 	size_t decoded_name_size;
 	size_t packet_size;
 	int rc = 0;
 
-	if ((name_size > ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE)
+	if ((mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)
+	    && !(mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
+	    && (name_size > ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE)
 	    && (strncmp(name, ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX,
 			ECRYPTFS_FNEK_ENCRYPTED_FILENAME_PREFIX_SIZE) == 0)) {
-		struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
-			&ecryptfs_superblock_to_private(
-				ecryptfs_dir_dentry->d_sb)->mount_crypt_stat;
 		const char *orig_name = name;
 		size_t orig_name_size = name_size;
 

fs/ecryptfs/ecryptfs_kernel.h

@@ -620,7 +620,6 @@ int ecryptfs_interpose(struct dentry *hidden_dentry,
 		       u32 flags);
 int ecryptfs_lookup_and_interpose_lower(struct dentry *ecryptfs_dentry,
 					struct dentry *lower_dentry,
-					struct ecryptfs_crypt_stat *crypt_stat,
 					struct inode *ecryptfs_dir_inode,
 					struct nameidata *ecryptfs_nd);
 int ecryptfs_decode_and_decrypt_filename(char **decrypted_name,

fs/ecryptfs/inode.c

@@ -246,7 +246,6 @@ out:
  */
 int ecryptfs_lookup_and_interpose_lower(struct dentry *ecryptfs_dentry,
 					struct dentry *lower_dentry,
-					struct ecryptfs_crypt_stat *crypt_stat,
 					struct inode *ecryptfs_dir_inode,
 					struct nameidata *ecryptfs_nd)
 {
@@ -254,6 +253,7 @@ int ecryptfs_lookup_and_interpose_lower(struct dentry *ecryptfs_dentry,
 	struct vfsmount *lower_mnt;
 	struct inode *lower_inode;
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
+	struct ecryptfs_crypt_stat *crypt_stat;
 	char *page_virt = NULL;
 	u64 file_size;
 	int rc = 0;
@@ -314,6 +314,11 @@ int ecryptfs_lookup_and_interpose_lower(struct dentry *ecryptfs_dentry,
 			goto out_free_kmem;
 		}
 	}
+	crypt_stat = &ecryptfs_inode_to_private(
+					ecryptfs_dentry->d_inode)->crypt_stat;
+	/* TODO: lock for crypt_stat comparison */
+	if (!(crypt_stat->flags & ECRYPTFS_POLICY_APPLIED))
+			ecryptfs_set_default_sizes(crypt_stat);
 	rc = ecryptfs_read_and_validate_header_region(page_virt,
 						      ecryptfs_dentry->d_inode);
 	if (rc) {
@@ -362,9 +367,7 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
 {
 	char *encrypted_and_encoded_name = NULL;
 	size_t encrypted_and_encoded_name_size;
-	struct ecryptfs_crypt_stat *crypt_stat = NULL;
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat = NULL;
-	struct ecryptfs_inode_info *inode_info;
 	struct dentry *lower_dir_dentry, *lower_dentry;
 	int rc = 0;
 
@@ -388,26 +391,15 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
 	}
 	if (lower_dentry->d_inode)
 		goto lookup_and_interpose;
-	inode_info =  ecryptfs_inode_to_private(ecryptfs_dentry->d_inode);
-	if (inode_info) {
-		crypt_stat = &inode_info->crypt_stat;
-		/* TODO: lock for crypt_stat comparison */
-		if (!(crypt_stat->flags & ECRYPTFS_POLICY_APPLIED))
-			ecryptfs_set_default_sizes(crypt_stat);
-	}
-	if (crypt_stat)
-		mount_crypt_stat = crypt_stat->mount_crypt_stat;
-	else
-		mount_crypt_stat = &ecryptfs_superblock_to_private(
-			ecryptfs_dentry->d_sb)->mount_crypt_stat;
-	if (!(crypt_stat && (crypt_stat->flags & ECRYPTFS_ENCRYPT_FILENAMES))
-	    && !(mount_crypt_stat && (mount_crypt_stat->flags
-				     & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)))
+	mount_crypt_stat = &ecryptfs_superblock_to_private(
+				ecryptfs_dentry->d_sb)->mount_crypt_stat;
+	if (!(mount_crypt_stat
+	    && (mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)))
 		goto lookup_and_interpose;
 	dput(lower_dentry);
 	rc = ecryptfs_encrypt_and_encode_filename(
 		&encrypted_and_encoded_name, &encrypted_and_encoded_name_size,
-		crypt_stat, mount_crypt_stat, ecryptfs_dentry->d_name.name,
+		NULL, mount_crypt_stat, ecryptfs_dentry->d_name.name,
 		ecryptfs_dentry->d_name.len);
 	if (rc) {
 		printk(KERN_ERR "%s: Error attempting to encrypt and encode "
@@ -426,7 +418,7 @@ static struct dentry *ecryptfs_lookup(struct inode *ecryptfs_dir_inode,
 	}
 lookup_and_interpose:
 	rc = ecryptfs_lookup_and_interpose_lower(ecryptfs_dentry, lower_dentry,
-						 crypt_stat, ecryptfs_dir_inode,
+						 ecryptfs_dir_inode,
 						 ecryptfs_nd);
 	goto out;
 out_d_drop: