linux-kernel - [PATCH] btrfs: harden parsing of compress mount option

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Message-ID: <20250423073329.4021878-1-neelx@suse.com>
Date: Wed, 23 Apr 2025 09:33:28 +0200
From: Daniel Vacek <neelx@...e.com>
To: Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>,
	David Sterba <dsterba@...e.com>,
	Nick Terrell <terrelln@...com>
Cc: Daniel Vacek <neelx@...e.com>,
	linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] btrfs: harden parsing of compress mount option

Btrfs happily but incorrectly accepts the `-o compress=zlib+foo` and similar
options with any random suffix. Let's handle that correctly.

Signed-off-by: Daniel Vacek <neelx@...e.com>
---
 fs/btrfs/super.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 40709e2a44fce..f7e064b8c6d88 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -354,7 +354,10 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			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 (strncmp(param->string, "zlib", 4) == 0 &&
+				(param->string[4] == ':' ||
+				 param->string[4] == ',' ||
+				 param->string[4] == '\0')) {
 			ctx->compress_type = BTRFS_COMPRESS_ZLIB;
 			ctx->compress_level =
 				btrfs_compress_str2level(BTRFS_COMPRESS_ZLIB,
@@ -362,13 +365,18 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			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 (strncmp(param->string, "lzo", 3) == 0 &&
+				(param->string[3] == ',' ||
+				 param->string[3] == '\0')) {
 			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 (strncmp(param->string, "zstd", 4) == 0 &&
+				(param->string[4] == ':' ||
+				 param->string[4] == ',' ||
+				 param->string[4] == '\0')) {
 			ctx->compress_type = BTRFS_COMPRESS_ZSTD;
 			ctx->compress_level =
 				btrfs_compress_str2level(BTRFS_COMPRESS_ZSTD,
@@ -376,7 +384,12 @@ static int btrfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			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 ((strncmp(param->string, "no", 2) == 0 &&
+				(param->string[2] == ',' ||
+				 param->string[2] == '\0')) ||
+			   (strncmp(param->string, "none", 4) == 0 &&
+				(param->string[4] == ',' ||
+				 param->string[4] == '\0'))) {
 			ctx->compress_level = 0;
 			ctx->compress_type = 0;
 			btrfs_clear_opt(ctx->mount_opt, COMPRESS);
-- 
2.47.2