[PATCH 15/15] smb: client: support trusted EAs on POSIX mounts

Register the trusted xattr handler and add trusted.* to the native
prefix table. The handler sends native trusted names only on negotiated
SMB3 POSIX mounts; non-POSIX user.trusted.* EAs retain their existing
user namespace mapping.

Hide native trusted names from listxattr callers without CAP_SYS_ADMIN.
Reject the XFS trusted.SGI_ACL_* names before matching the trusted
prefix.

Run the following as root on a POSIX mount to check that a write clears
security.capability without removing trusted.name:

  $ CIFS_MNT=/path/to/cifs-mount
  $ file="$CIFS_MNT/trusted-preserve"
  $ touch "$file"
  $ setfattr -n trusted.name -v value "$file"
  $ printf 'data\n' >> "$file"

Signed-off-by: Ze Tan <[email protected]>
---
 fs/smb/client/cifsfs.h  |  1 +
 fs/smb/client/smb2ops.c |  3 +++
 fs/smb/client/xattr.c   | 51 +++++++++++++++++++++++++++++++++++++----
 3 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/fs/smb/client/cifsfs.h b/fs/smb/client/cifsfs.h
index 4ab1a203be3e..1c04dc07a2ff 100644
--- a/fs/smb/client/cifsfs.h
+++ b/fs/smb/client/cifsfs.h
@@ -136,6 +136,7 @@ int cifs_symlink(struct mnt_idmap *idmap, struct inode *inode,
 enum cifs_ea_name_type {
 	CIFS_EA_USER,
 	CIFS_EA_NATIVE,
+	CIFS_EA_HIDDEN,
 };
 
 enum cifs_ea_name_type
diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index fd778d903e93..f38230e4c31d 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -1103,6 +1103,8 @@ move_smb2_ea_to_cifs(char *dst, size_t dst_size,
 
 			name_type = cifs_ea_name_type(name, name_len,
 						     posix_extensions);
+			if (name_type == CIFS_EA_HIDDEN)
+				goto next;
 			if (name_type == CIFS_EA_NATIVE)
 				user_name_len = name_len + 1;
 			else
@@ -1130,6 +1132,7 @@ move_smb2_ea_to_cifs(char *dst, size_t dst_size,
 			}
 		}
 
+next:
 		if (!src->next_entry_offset)
 			break;
 
diff --git a/fs/smb/client/xattr.c b/fs/smb/client/xattr.c
index 59f6655a1b34..4b6736a6b375 100644
--- a/fs/smb/client/xattr.c
+++ b/fs/smb/client/xattr.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/fs.h>
+#include <linux/capability.h>
 #include <linux/posix_acl_xattr.h>
 #include <linux/slab.h>
 #include <linux/xattr.h>
@@ -36,7 +37,7 @@
 #define SMB3_XATTR_CIFS_NTSD_FULL "system.smb3_ntsd_full" /* owner/DACL/SACL */
 #define SMB3_XATTR_ATTRIB "smb3.dosattrib"  /* full name: user.smb3.dosattrib */
 #define SMB3_XATTR_CREATETIME "smb3.creationtime"  /* user.smb3.creationtime */
-enum { XATTR_USER, XATTR_SECURITY,
+enum { XATTR_USER, XATTR_TRUSTED, XATTR_SECURITY,
 	XATTR_CIFS_ACL, XATTR_ACL_ACCESS, XATTR_ACL_DEFAULT,
 	XATTR_CIFS_NTSD_SACL, XATTR_CIFS_NTSD_OWNER,
 	XATTR_CIFS_NTSD, XATTR_CIFS_NTSD_FULL };
@@ -46,6 +47,15 @@ static const char * const cifs_native_xattr_names[] = {
 	XATTR_SECURITY_PREFIX "xfstests",
 };
 
+static const char * const cifs_native_xattr_prefixes[] = {
+	XATTR_TRUSTED_PREFIX,
+};
+
+static const char * const cifs_unsupported_xattr_names[] = {
+	XATTR_TRUSTED_PREFIX "SGI_ACL_FILE",
+	XATTR_TRUSTED_PREFIX "SGI_ACL_DEFAULT",
+};
+
 enum cifs_ea_name_type
 cifs_ea_name_type(const char *name, size_t name_len, bool posix_extensions)
 {
@@ -54,6 +64,14 @@ cifs_ea_name_type(const char *name, size_t name_len, bool posix_extensions)
 	if (!posix_extensions)
 		return CIFS_EA_USER;
 
+	for (i = 0; i < ARRAY_SIZE(cifs_unsupported_xattr_names); i++) {
+		size_t xattr_len = strlen(cifs_unsupported_xattr_names[i]);
+
+		if (name_len == xattr_len &&
+		    !memcmp(name, cifs_unsupported_xattr_names[i], name_len))
+			return CIFS_EA_HIDDEN;
+	}
+
 	for (i = 0; i < ARRAY_SIZE(cifs_native_xattr_names); i++) {
 		size_t xattr_len = strlen(cifs_native_xattr_names[i]);
 
@@ -62,6 +80,15 @@ cifs_ea_name_type(const char *name, size_t name_len, bool posix_extensions)
 			return CIFS_EA_NATIVE;
 	}
 
+	for (i = 0; i < ARRAY_SIZE(cifs_native_xattr_prefixes); i++) {
+		size_t prefix_len = strlen(cifs_native_xattr_prefixes[i]);
+
+		if (name_len > prefix_len &&
+		    !memcmp(name, cifs_native_xattr_prefixes[i], prefix_len))
+			return capable(CAP_SYS_ADMIN) ? CIFS_EA_NATIVE :
+						       CIFS_EA_HIDDEN;
+	}
+
 	return CIFS_EA_USER;
 }
 
@@ -76,6 +103,10 @@ static int cifs_build_ea_name(int xattr_flag, const char *name, char *ea_name,
 		prefix = XATTR_SECURITY_PREFIX;
 		prefix_len = XATTR_SECURITY_PREFIX_LEN;
 		break;
+	case XATTR_TRUSTED:
+		prefix = XATTR_TRUSTED_PREFIX;
+		prefix_len = XATTR_TRUSTED_PREFIX_LEN;
+		break;
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -186,6 +217,7 @@ static int cifs_xattr_set(const struct xattr_handler *handler,
 	}
 
 	switch (handler->flags) {
+	case XATTR_TRUSTED:
 	case XATTR_SECURITY:
 		if (!pTcon->posix_extensions)
 			goto out;
@@ -195,8 +227,8 @@ static int cifs_xattr_set(const struct xattr_handler *handler,
 			goto out;
 		server_ea_name = ea_name;
 		lease_inode = inode;
-		cifs_dbg(FYI, "%s: setting security xattr %s\n",
-			 __func__, name);
+		cifs_dbg(FYI, "%s: setting native xattr %s\n",
+			 __func__, server_ea_name);
 		goto set_ea;
 
 	case XATTR_USER:
@@ -372,6 +404,7 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 
 	/* return alt name if available as pseudo attr */
 	switch (handler->flags) {
+	case XATTR_TRUSTED:
 	case XATTR_SECURITY:
 		if (!pTcon->posix_extensions)
 			goto out;
@@ -381,8 +414,8 @@ static int cifs_xattr_get(const struct xattr_handler *handler,
 			goto out;
 		server_ea_name = ea_name;
 		lease_inode = inode;
-		cifs_dbg(FYI, "%s: querying security xattr %s\n",
-			 __func__, name);
+		cifs_dbg(FYI, "%s: querying native xattr %s\n",
+			 __func__, server_ea_name);
 		goto query_ea;
 
 	case XATTR_USER:
@@ -531,6 +564,13 @@ static const struct xattr_handler cifs_user_xattr_handler = {
 	.set = cifs_xattr_set,
 };
 
+static const struct xattr_handler cifs_trusted_xattr_handler = {
+	.prefix = XATTR_TRUSTED_PREFIX,
+	.flags = XATTR_TRUSTED,
+	.get = cifs_xattr_get,
+	.set = cifs_xattr_set,
+};
+
 static const struct xattr_handler cifs_security_xattr_handler = {
 	.prefix = XATTR_SECURITY_PREFIX,
 	.flags = XATTR_SECURITY,
@@ -622,6 +662,7 @@ static const struct xattr_handler smb3_ntsd_full_xattr_handler = {
 
 const struct xattr_handler * const cifs_xattr_handlers[] = {
 	&cifs_user_xattr_handler,
+	&cifs_trusted_xattr_handler,
 	&cifs_security_xattr_handler,
 	&cifs_os2_xattr_handler,
 	&cifs_cifs_acl_xattr_handler,
-- 
2.43.0