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SubjectRe: [patch 7/9] unprivileged mounts: allow unprivileged fuse mounts
Quoting Miklos Szeredi (miklos@szeredi.hu):
> From: Miklos Szeredi <mszeredi@suse.cz>
>
> 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@suse.cz>

Sounds like a sysctl to enable FS_SAFE for fuse will make this patch
acceptable to everyone?

> ---
>
> 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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