[patch 7/9] unprivileged mounts: allow unprivileged fuse mounts

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Use FS_SAFE for "fuse" fs type, but not for "fuseblk".

FUSE was designed from the beginning to be safe for unprivileged users.  This
has also been verified in practice over many years.  In addition unprivileged
mounts require the parent mount to be owned by the user, which is more strict
than the current userspace policy.

This will enable future installations to remove the suid-root fusermount
utility.

Don't require the "user_id=" and "group_id=" options for unprivileged mounts,
but if they are present, verify them for sanity.

Disallow the "allow_other" option for unprivileged mounts.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---

Index: linux/fs/fuse/inode.c
===================================================================
--- linux.orig/fs/fuse/inode.c	2008-01-03 17:13:13.000000000 +0100
+++ linux/fs/fuse/inode.c	2008-01-03 21:28:01.000000000 +0100
@@ -357,6 +357,19 @@ static int parse_fuse_opt(char *opt, str
 	d->max_read = ~0;
 	d->blksize = 512;
 
+	/*
+	 * For unprivileged mounts use current uid/gid.  Still allow
+	 * "user_id" and "group_id" options for compatibility, but
+	 * only if they match these values.
+	 */
+	if (!capable(CAP_SYS_ADMIN)) {
+		d->user_id = current->uid;
+		d->user_id_present = 1;
+		d->group_id = current->gid;
+		d->group_id_present = 1;
+
+	}
+
 	while ((p = strsep(&opt, ",")) != NULL) {
 		int token;
 		int value;
@@ -385,6 +398,8 @@ static int parse_fuse_opt(char *opt, str
 		case OPT_USER_ID:
 			if (match_int(&args[0], &value))
 				return 0;
+			if (d->user_id_present && d->user_id != value)
+				return 0;
 			d->user_id = value;
 			d->user_id_present = 1;
 			break;
@@ -392,6 +407,8 @@ static int parse_fuse_opt(char *opt, str
 		case OPT_GROUP_ID:
 			if (match_int(&args[0], &value))
 				return 0;
+			if (d->group_id_present && d->group_id != value)
+				return 0;
 			d->group_id = value;
 			d->group_id_present = 1;
 			break;
@@ -596,6 +613,10 @@ static int fuse_fill_super(struct super_
 	if (!parse_fuse_opt((char *) data, &d, is_bdev))
 		return -EINVAL;
 
+	/* This is a privileged option */
+	if ((d.flags & FUSE_ALLOW_OTHER) && !capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	if (is_bdev) {
 #ifdef CONFIG_BLOCK
 		if (!sb_set_blocksize(sb, d.blksize))
@@ -696,9 +717,9 @@ static int fuse_get_sb(struct file_syste
 static struct file_system_type fuse_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "fuse",
-	.fs_flags	= FS_HAS_SUBTYPE,
 	.get_sb		= fuse_get_sb,
 	.kill_sb	= kill_anon_super,
+	.fs_flags	= FS_HAS_SUBTYPE | FS_SAFE,
 };
 
 #ifdef CONFIG_BLOCK

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