[PATCH v3 2/2] btrfs: harden parsing of compress mount options

[Daniel Vacek <neelx@suse.com>]

Btrfs happily but incorrectly accepts the `-o compress=zlib+foo` and similar
options with any random suffix.

Fix that by explicitly checking the end of the strings.

Signed-off-by: Daniel Vacek <neelx@suse.com>
---
v3 changes: Split into two patches to ease backporting,
            no functional changes.

 fs/btrfs/super.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 6291ab45ab2a5..4510c5f7a785e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -270,9 +270,20 @@ static inline blk_mode_t btrfs_open_mode(struct fs_context *fc)
 	return sb_open_mode(fc->sb_flags) & ~BLK_OPEN_RESTRICT_WRITES;
 }
 
+static bool btrfs_match_compress_type(char *string, char *type, bool may_have_level)
+{
+	int len = strlen(type);
+
+	return strncmp(string, type, len) == 0 &&
+		((may_have_level && string[len] == ':') ||
+				    string[len] == '\0');
+}
+
 static int btrfs_parse_compress(struct btrfs_fs_context *ctx,
 				struct fs_parameter *param, int opt)
 {
+	char *string = param->string;
+
 	/*
 	 * Provide the same semantics as older kernels that don't use fs
 	 * context, specifying the "compress" option clears
@@ -288,36 +299,37 @@ static int btrfs_parse_compress(struct btrfs_fs_context *ctx,
 		btrfs_set_opt(ctx->mount_opt, COMPRESS);
 		btrfs_clear_opt(ctx->mount_opt, NODATACOW);
 		btrfs_clear_opt(ctx->mount_opt, NODATASUM);
-	} else if (strncmp(param->string, "zlib", 4) == 0) {
+	} else if (btrfs_match_compress_type(string, "zlib", true)) {
 		ctx->compress_type = BTRFS_COMPRESS_ZLIB;
 		ctx->compress_level =
 			btrfs_compress_str2level(BTRFS_COMPRESS_ZLIB,
-						 param->string + 4);
+						 string + 4);
 		btrfs_set_opt(ctx->mount_opt, COMPRESS);
 		btrfs_clear_opt(ctx->mount_opt, NODATACOW);
 		btrfs_clear_opt(ctx->mount_opt, NODATASUM);
-	} else if (strncmp(param->string, "lzo", 3) == 0) {
+	} else if (btrfs_match_compress_type(string, "lzo", false)) {
 		ctx->compress_type = BTRFS_COMPRESS_LZO;
 		ctx->compress_level = 0;
 		btrfs_set_opt(ctx->mount_opt, COMPRESS);
 		btrfs_clear_opt(ctx->mount_opt, NODATACOW);
 		btrfs_clear_opt(ctx->mount_opt, NODATASUM);
-	} else if (strncmp(param->string, "zstd", 4) == 0) {
+	} else if (btrfs_match_compress_type(string, "zstd", true)) {
 		ctx->compress_type = BTRFS_COMPRESS_ZSTD;
 		ctx->compress_level =
 			btrfs_compress_str2level(BTRFS_COMPRESS_ZSTD,
-						 param->string + 4);
+						 string + 4);
 		btrfs_set_opt(ctx->mount_opt, COMPRESS);
 		btrfs_clear_opt(ctx->mount_opt, NODATACOW);
 		btrfs_clear_opt(ctx->mount_opt, NODATASUM);
-	} else if (strncmp(param->string, "no", 2) == 0) {
+	} else if (btrfs_match_compress_type(string, "no", false) ||
+		   btrfs_match_compress_type(string, "none", false)) {
 		ctx->compress_level = 0;
 		ctx->compress_type = 0;
 		btrfs_clear_opt(ctx->mount_opt, COMPRESS);
 		btrfs_clear_opt(ctx->mount_opt, FORCE_COMPRESS);
 	} else {
 		btrfs_err(NULL, "unrecognized compression value %s",
-			  param->string);
+			  string);
 		return -EINVAL;
 	}
 	return 0;
-- 
2.47.2