btrfs: harden parsing of compression mount options

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>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 408ce5418c18992726f2b656332bb5b04cd84cdb..73c6c5b9b07a6c0240307276b4a8515d941613a2 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -267,9 +267,19 @@ 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(const char *string, const char *type, bool may_have_level)
+{
+       const 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,
                                const struct fs_parameter *param, int opt)
 {
+       const char *string = param->string;
+
        /*
         * Provide the same semantics as older kernels that don't use fs
         * context, specifying the "compress" option clears "force-compress"
@@ -285,33 +295,34 @@ 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);
+               btrfs_err(NULL, "unrecognized compression value %s", string);
                return -EINVAL;
        }
        return 0;