linux-ext4 - [PATCH 23/29] fuse2fs: check for supported xattr name prefixes

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Message-ID: <174786677959.1383760.12099114841852662650.stgit@frogsfrogsfrogs>
Date: Wed, 21 May 2025 15:40:55 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: linux-ext4@...r.kernel.org
Subject: [PATCH 23/29] fuse2fs: check for supported xattr name prefixes

From: Darrick J. Wong <djwong@...nel.org>

Ignore any xattr calls for name prefixes that the kernel doesn't also
support.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 lib/ext2fs/ext2fsP.h |    3 +++
 misc/fuse2fs.c       |   37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)


diff --git a/lib/ext2fs/ext2fsP.h b/lib/ext2fs/ext2fsP.h
index d1f2105e9813ca..428081c9e2ff38 100644
--- a/lib/ext2fs/ext2fsP.h
+++ b/lib/ext2fs/ext2fsP.h
@@ -214,4 +214,7 @@ typedef void (*ext2_exit_fn)(void *);
 errcode_t ext2fs_add_exit_fn(ext2_exit_fn fn, void *data);
 errcode_t ext2fs_remove_exit_fn(ext2_exit_fn fn, void *data);
 
+#define ARRAY_SIZE(array)			\
+        (sizeof(array) / sizeof(array[0]))
+
 #define EXT2FS_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2*!!(cond)]))
diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index 74bbe661a417e5..28b77d367cf705 100644
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -2443,6 +2443,27 @@ static int op_statfs(const char *path EXT2FS_ATTR((unused)),
 	return 0;
 }
 
+static const char *valid_xattr_prefixes[] = {
+	"user.",
+	"trusted.",
+	"security.",
+	"gnu.",
+	"system.",
+};
+
+static int validate_xattr_name(const char *name)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(valid_xattr_prefixes); i++) {
+		if (!strncmp(name, valid_xattr_prefixes[i],
+					strlen(valid_xattr_prefixes[i])))
+			return 1;
+	}
+
+	return 0;
+}
+
 static int op_getxattr(const char *path, const char *key, char *value,
 		       size_t len)
 {
@@ -2456,6 +2477,9 @@ static int op_getxattr(const char *path, const char *key, char *value,
 	errcode_t err;
 	int ret = 0;
 
+	if (!validate_xattr_name(key))
+		return -ENODATA;
+
 	FUSE2FS_CHECK_CONTEXT(ff);
 	fs = ff->fs;
 	pthread_mutex_lock(&ff->bfl);
@@ -2626,6 +2650,9 @@ static int op_setxattr(const char *path EXT2FS_ATTR((unused)),
 	if (flags & ~(XATTR_CREATE | XATTR_REPLACE))
 		return -EOPNOTSUPP;
 
+	if (!validate_xattr_name(key))
+		return -EINVAL;
+
 	FUSE2FS_CHECK_CONTEXT(ff);
 	fs = ff->fs;
 	pthread_mutex_lock(&ff->bfl);
@@ -2714,6 +2741,16 @@ static int op_removexattr(const char *path, const char *key)
 	errcode_t err;
 	int ret = 0;
 
+	/*
+	 * Once in a while libfuse gives us a no-name xattr to delete as part
+	 * of clearing ACLs.  Just pretend we cleared them.
+	 */
+	if (key[0] == 0)
+		return 0;
+
+	if (!validate_xattr_name(key))
+		return -ENODATA;
+
 	FUSE2FS_CHECK_CONTEXT(ff);
 	fs = ff->fs;
 	pthread_mutex_lock(&ff->bfl);