LSM: lift extracting and parsing LSM options into the caller of ->sb_remount()

This paves the way for retaining the LSM options from a common filesystem
mount context during a mount parameter parsing phase to be instituted prior
to actual mount/reconfiguration actions.

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namespace.c

@@ -2299,6 +2299,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	int err;
 	struct super_block *sb = path->mnt->mnt_sb;
 	struct mount *mnt = real_mount(path->mnt);
+	struct security_mnt_opts opts;
 
 	if (!check_mnt(mnt))
 		return -EINVAL;
@@ -2309,7 +2310,23 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 	if (!can_change_locked_flags(mnt, mnt_flags))
 		return -EPERM;
 
-	err = security_sb_remount(sb, data);
+	security_init_mnt_opts(&opts);
+	if (data && !(sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)) {
+		char *secdata = alloc_secdata();
+		if (!secdata)
+			return -ENOMEM;
+		err = security_sb_copy_data(data, secdata);
+		if (err) {
+			free_secdata(secdata);
+			return err;
+		}
+		err = security_sb_parse_opts_str(secdata, &opts);
+		free_secdata(secdata);
+		if (err)
+			return err;
+	}
+	err = security_sb_remount(sb, &opts);
+	security_free_mnt_opts(&opts);
 	if (err)
 		return err;
 

include/linux/lsm_hooks.h

@@ -1462,7 +1462,8 @@ union security_list_options {
 	int (*sb_alloc_security)(struct super_block *sb);
 	void (*sb_free_security)(struct super_block *sb);
 	int (*sb_copy_data)(char *orig, char *copy);
-	int (*sb_remount)(struct super_block *sb, void *data);
+	int (*sb_remount)(struct super_block *sb,
+			  struct security_mnt_opts *opts);
 	int (*sb_kern_mount)(struct super_block *sb, int flags,
 			     struct security_mnt_opts *opts);
 	int (*sb_show_options)(struct seq_file *m, struct super_block *sb);

include/linux/security.h

@@ -249,7 +249,7 @@ void security_bprm_committed_creds(struct linux_binprm *bprm);
 int security_sb_alloc(struct super_block *sb);
 void security_sb_free(struct super_block *sb);
 int security_sb_copy_data(char *orig, char *copy);
-int security_sb_remount(struct super_block *sb, void *data);
+int security_sb_remount(struct super_block *sb, struct security_mnt_opts *opts);
 int security_sb_kern_mount(struct super_block *sb, int flags,
 			   struct security_mnt_opts *opts);
 int security_sb_show_options(struct seq_file *m, struct super_block *sb);
@@ -561,7 +561,8 @@ static inline int security_sb_copy_data(char *orig, char *copy)
 	return 0;
 }
 
-static inline int security_sb_remount(struct super_block *sb, void *data)
+static inline int security_sb_remount(struct super_block *sb,
+				      struct security_mnt_opts *opts)
 {
 	return 0;
 }

security/security.c

@@ -390,9 +390,10 @@ int security_sb_copy_data(char *orig, char *copy)
 }
 EXPORT_SYMBOL(security_sb_copy_data);
 
-int security_sb_remount(struct super_block *sb, void *data)
+int security_sb_remount(struct super_block *sb,
+			struct security_mnt_opts *opts)
 {
-	return call_int_hook(sb_remount, 0, sb, data);
+	return call_int_hook(sb_remount, 0, sb, opts);
 }
 
 int security_sb_kern_mount(struct super_block *sb, int flags,

security/selinux/hooks.c

@@ -2812,39 +2812,22 @@ static int selinux_sb_copy_data(char *orig, char *copy)
 	return rc;
 }
 
-static int selinux_sb_remount(struct super_block *sb, void *data)
+static int selinux_sb_remount(struct super_block *sb,
+			      struct security_mnt_opts *opts)
 {
-	int rc, i, *flags;
-	struct security_mnt_opts opts;
-	char *secdata, **mount_options;
+	int i, *flags;
+	char **mount_options;
 	struct superblock_security_struct *sbsec = sb->s_security;
 
 	if (!(sbsec->flags & SE_SBINITIALIZED))
 		return 0;
 
-	if (!data)
-		return 0;
+	mount_options = opts->mnt_opts;
+	flags = opts->mnt_opts_flags;
 
-	if (sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)
-		return 0;
-
-	security_init_mnt_opts(&opts);
-	secdata = alloc_secdata();
-	if (!secdata)
-		return -ENOMEM;
-	rc = selinux_sb_copy_data(data, secdata);
-	if (rc)
-		goto out_free_secdata;
-
-	rc = selinux_parse_opts_str(secdata, &opts);
-	if (rc)
-		goto out_free_secdata;
-
-	mount_options = opts.mnt_opts;
-	flags = opts.mnt_opts_flags;
-
-	for (i = 0; i < opts.num_mnt_opts; i++) {
+	for (i = 0; i < opts->num_mnt_opts; i++) {
 		u32 sid;
+		int rc;
 
 		if (flags[i] == SBLABEL_MNT)
 			continue;
@@ -2855,9 +2838,8 @@ static int selinux_sb_remount(struct super_block *sb, void *data)
 			pr_warn("SELinux: security_context_str_to_sid"
 			       "(%s) failed for (dev %s, type %s) errno=%d\n",
 			       mount_options[i], sb->s_id, sb->s_type->name, rc);
-			goto out_free_opts;
+			return rc;
 		}
-		rc = -EINVAL;
 		switch (flags[i]) {
 		case FSCONTEXT_MNT:
 			if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid, sid))
@@ -2880,21 +2862,16 @@ static int selinux_sb_remount(struct super_block *sb, void *data)
 				goto out_bad_option;
 			break;
 		default:
-			goto out_free_opts;
+			return -EINVAL;
 		}
 	}
+	return 0;
 
-	rc = 0;
-out_free_opts:
-	security_free_mnt_opts(&opts);
-out_free_secdata:
-	free_secdata(secdata);
-	return rc;
 out_bad_option:
 	pr_warn("SELinux: unable to change security options "
 	       "during remount (dev %s, type=%s)\n", sb->s_id,
 	       sb->s_type->name);
-	goto out_free_opts;
+	return -EINVAL;
 }
 
 static int selinux_sb_kern_mount(struct super_block *sb, int flags,