e2fsck: check for encrypted directory entries with too-short file names

If there are directory entries with file names which are less than 16
bytes, it turns out that passing less than the crypto block size to
the kernel's crypto layer will cause the kernel to crash.

However, since there never should be encrypted directory entries where
the file name is less than 16 bytes (the AES block size), change
e2fsck to offer to address this corruption by deleting the directory
entry.

(We need to checks for this condition into the kernel as well.)

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

e2fsck/pass2.c

@@ -494,6 +494,20 @@ static int check_name(e2fsck_t ctx,
 	return ret;
 }
 
+static int encrypted_check_name(e2fsck_t ctx,
+				struct ext2_dir_entry *dirent,
+				struct problem_context *pctx)
+{
+	if (ext2fs_dirent_name_len(dirent) < EXT4_CRYPTO_BLOCK_SIZE) {
+		if (fix_problem(ctx, PR_2_BAD_ENCRYPTED_NAME, pctx)) {
+			dirent->inode = 0;
+			return 1;
+		}
+		ext2fs_unmark_valid(ctx->fs);
+	}
+	return 0;
+}
+
 /*
  * Check the directory filetype (if present)
  */
@@ -1383,6 +1397,12 @@ skip_checksum:
 		if (!encrypted && check_name(ctx, dirent, &cd->pctx))
 			dir_modified++;
 
+		if (encrypted && (dot_state) > 1 &&
+		    encrypted_check_name(ctx, dirent, &cd->pctx)) {
+			dir_modified++;
+			goto next;
+		}
+
 		if (check_filetype(ctx, dirent, ino, &cd->pctx))
 			dir_modified++;
 

e2fsck/problem.c

@@ -1613,6 +1613,11 @@ static struct e2fsck_problem problem_table[] = {
 	  N_("Fixing size of inline @d @i %i failed.\n"),
 	  PROMPT_TRUNCATE, 0 },
 
+	/* Encrypted directory entry is too short */
+	{ PR_2_BAD_ENCRYPTED_NAME,
+	  N_("Encrypted @E is too short.\n"),
+	  PROMPT_CLEAR, 0 },
+
 	/* Pass 3 errors */
 
 	/* Pass 3: Checking directory connectivity */

e2fsck/problem.h

@@ -963,6 +963,9 @@ struct problem_context {
 /* fixing inline dir size failed */
 #define PR_2_FIX_INLINE_DIR_FAILED	0x02004F
 
+/* Encrypted directory entry is too short */
+#define PR_2_BAD_ENCRYPTED_NAME		0x020050
+
 /*
  * Pass 3 errors
  */

lib/ext2fs/ext2_fs.h

@@ -579,6 +579,7 @@ struct ext2_inode_large {
 #define EXT4_MAX_KEY_SIZE			64
 
 #define EXT4_KEY_DESCRIPTOR_SIZE		8
+#define EXT4_CRYPTO_BLOCK_SIZE			16
 
 /* Password derivation constants */
 #define EXT4_MAX_PASSPHRASE_SIZE		1024

tests/f_short_encrypted_dirent/expect.1

@@ -0,0 +1,17 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Encrypted entry 'motd' in /get_shorty (12) is too short.
+Clear? yes
+
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Unattached inode 13
+Connect to /lost+found? yes
+
+Inode 13 ref count is 2, should be 1.  Fix? yes
+
+Pass 5: Checking group summary information
+
+test_filesys: ***** FILE SYSTEM WAS MODIFIED *****
+test_filesys: 13/16 files (0.0% non-contiguous), 23/100 blocks
+Exit status is 1

tests/f_short_encrypted_dirent/expect.2

@@ -0,0 +1,7 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+test_filesys: 13/16 files (0.0% non-contiguous), 23/100 blocks
+Exit status is 0

tests/f_short_encrypted_dirent/name

@@ -0,0 +1 @@
+short encrypted directory entry