[PATCH v6 2/6] btrfs: also validate compression levels in btrfs_compress_is_valid_type()

[koraynilay <koray.fra@gmail.com>]

Change btrfs_compress_is_valid_type() to use btrfs_match_compress_type()
and btrfs_compress_str2level() instead of a simple strncmp(), which would
validate even incorrect strings (e.g. "zstd:invalid" or "zstdinvalid").

This also makes the function validate levels in the same way the
compress= option gets parsed, allowing bigger or smaller values, but
still clamping them to the min or max supported.

Furthermore, remove the len parameter, since now it requires a
NUL-terminated string because of btrfs_compress_str2level(); this change
is fine because btrfs_compress_is_valid_type() is used only once in
props.c by prop_compression_validate(), which now uses a stack-based
buffer and memcpy() to convert the user-supplied xattr value to a
NUL-terminated string.

Assisted-by: Gemini:3.1-pro antigravity-cli-1.1.5
Signed-off-by: koraynilay <koray.fra@gmail.com>
---
 fs/btrfs/compression.c | 18 +++++++++++++++---
 fs/btrfs/compression.h |  2 +-
 fs/btrfs/props.c       | 18 +++++++++++++++++-
 3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 2880ee1f80d1..de10d96aee8a 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -70,18 +70,30 @@ static struct compressed_bio *alloc_compressed_bio(struct btrfs_inode *inode,
 	return to_compressed_bio(bbio);
 }
 
-bool btrfs_compress_is_valid_type(const char *str, size_t len)
+/**
+ * btrfs_compress_is_valid_type - Check if a string is a valid compression type.
+ * @str: The compression string to check. Must be null-terminated.
+ *
+ * Return: %true if the string is a valid compression algorithm (optionally with
+ * a level suffix, e.g. "zstd" or "zstd:9"), %false otherwise.
+ */
+bool btrfs_compress_is_valid_type(const char *str)
 {
+	size_t len = strlen(str);
 	int i;
 
 	for (i = 1; i < ARRAY_SIZE(btrfs_compress_types); i++) {
 		size_t comp_len = strlen(btrfs_compress_types[i]);
+		const char *comp_type = btrfs_compress_types[i];
+		int tmp_level;
 
 		if (len < comp_len)
 			continue;
 
-		if (!strncmp(btrfs_compress_types[i], str, comp_len))
-			return true;
+		if (btrfs_match_compress_type(str, comp_type, true)) {
+			if (btrfs_compress_str2level(i, str + comp_len, &tmp_level) == 0)
+				return true;
+		}
 	}
 	return false;
 }
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index e67ba47b4cdc..c63bed9f4152 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -132,7 +132,7 @@ extern const struct btrfs_compress_levels btrfs_lzo_compress;
 extern const struct btrfs_compress_levels btrfs_zstd_compress;
 
 const char* btrfs_compress_type2str(enum btrfs_compression_type type);
-bool btrfs_compress_is_valid_type(const char *str, size_t len);
+bool btrfs_compress_is_valid_type(const char *str);
 
 int btrfs_compress_heuristic(struct btrfs_inode *inode, u64 start, u64 end);
 
diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
index bb77d46376d4..2e706093e186 100644
--- a/fs/btrfs/props.c
+++ b/fs/btrfs/props.c
@@ -18,6 +18,15 @@
 #include "super.h"
 #include "dir-item.h"
 
+/*
+ * Max length of compression algorithm:level string.
+ *
+ * For now the longest possible string is "zstd:-15", which is
+ * 8 characters + 1 terminating null byte.
+ * Rounding it up to the closest power of 2 gives 16.
+ */
+#define BTRFS_COMPRESS_PROP_MAX_LEN 16
+
 #define BTRFS_PROP_HANDLERS_HT_BITS 8
 static DEFINE_HASHTABLE(prop_handlers_ht, BTRFS_PROP_HANDLERS_HT_BITS);
 
@@ -295,13 +304,20 @@ int btrfs_load_inode_props(struct btrfs_inode *inode, struct btrfs_path *path)
 static int prop_compression_validate(const struct btrfs_inode *inode,
 				     const char *value, size_t len)
 {
+	char value_str[BTRFS_COMPRESS_PROP_MAX_LEN];
+
 	if (!btrfs_inode_can_compress(inode))
 		return -EINVAL;
 
 	if (!value)
 		return 0;
 
-	if (btrfs_compress_is_valid_type(value, len))
+	if (len >= BTRFS_COMPRESS_PROP_MAX_LEN)
+		return -EINVAL;
+
+	memcpy(value_str, value, len);
+	value_str[len] = '\0';
+	if (btrfs_compress_is_valid_type(value_str))
 		return 0;
 
 	if ((len == 2 && strncmp("no", value, 2) == 0) ||
-- 
2.55.0