fscrypt: improve warning messages for unsupported encryption contexts

When fs/crypto/ encounters an inode with an invalid encryption context,
currently it prints a warning if the pair of encryption modes are
unrecognized, but it's silent if there are other problems such as
unsupported context size, format, or flags.  To help people debug such
situations, add more warning messages.
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/crypto/keyinfo.c

@@ -510,8 +510,12 @@ int fscrypt_get_encryption_info(struct inode *inode)
 	res = inode->i_sb->s_cop->get_context(inode, &ctx, sizeof(ctx));
 	if (res < 0) {
 		if (!fscrypt_dummy_context_enabled(inode) ||
-		    IS_ENCRYPTED(inode))
+		    IS_ENCRYPTED(inode)) {
+			fscrypt_warn(inode,
+				     "Error %d getting encryption context",
+				     res);
 			return res;
+		}
 		/* Fake up a context for an unencrypted directory */
 		memset(&ctx, 0, sizeof(ctx));
 		ctx.format = FS_ENCRYPTION_CONTEXT_FORMAT_V1;
@@ -519,14 +523,22 @@ int fscrypt_get_encryption_info(struct inode *inode)
 		ctx.filenames_encryption_mode = FS_ENCRYPTION_MODE_AES_256_CTS;
 		memset(ctx.master_key_descriptor, 0x42, FS_KEY_DESCRIPTOR_SIZE);
 	} else if (res != sizeof(ctx)) {
+		fscrypt_warn(inode,
+			     "Unknown encryption context size (%d bytes)", res);
 		return -EINVAL;
 	}
 
-	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1)
+	if (ctx.format != FS_ENCRYPTION_CONTEXT_FORMAT_V1) {
+		fscrypt_warn(inode, "Unknown encryption context version (%d)",
+			     ctx.format);
 		return -EINVAL;
+	}
 
-	if (ctx.flags & ~FS_POLICY_FLAGS_VALID)
+	if (ctx.flags & ~FS_POLICY_FLAGS_VALID) {
+		fscrypt_warn(inode, "Unknown encryption context flags (0x%02x)",
+			     ctx.flags);
 		return -EINVAL;
+	}
 
 	crypt_info = kmem_cache_zalloc(fscrypt_info_cachep, GFP_NOFS);
 	if (!crypt_info)