From feb8ae43a7b33148028829b1b1691b28c874c952 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 12 May 2019 13:18:42 -0400 Subject: start massaging the checks in sget_...(): move to sget_userns() there are 3 remaining callers of sget_userns() - sget(), mount_ns() and mount_pseudo_xattr(). Extra check in sget() is conditional upon mount being neither KERNMOUNT nor SUBMOUNT, the identical one in mount_ns() - upon being not KERNMOUNT; mount_pseudo_xattr() has no such checks at all. However, mount_ns() is never used with SUBMOUNT and mount_pseudo_xattr() is used only for KERNMOUNT, so both would be fine with the same logics as currently done in sget(), allowing to consolidate the entire thing in sget_userns() itself. That's not where these checks will end up in the long run, though - the whole reason why they'd been done so deep in the bowels of mount(2) was that there had been no way for a filesystem to specify which userns to look at until it has entered ->mount(). Now there is a place where filesystem could override the defaults - ->init_fs_context(). Which allows to pull the checks out into the callers of vfs_get_tree(). That'll take quite a bit of massage, but that mess is possible to tease apart. Signed-off-by: Al Viro --- fs/super.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) (limited to 'fs') diff --git a/fs/super.c b/fs/super.c index 2739f57515f8..9c371a04e1b6 100644 --- a/fs/super.c +++ b/fs/super.c @@ -583,6 +583,10 @@ struct super_block *sget_userns(struct file_system_type *type, struct super_block *old; int err; + /* Ensure the requestor has permissions over the target filesystem */ + if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN)) + return ERR_PTR(-EPERM); + if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !(type->fs_flags & FS_USERNS_MOUNT) && !capable(CAP_SYS_ADMIN)) @@ -653,10 +657,6 @@ struct super_block *sget(struct file_system_type *type, if (flags & SB_SUBMOUNT) user_ns = &init_user_ns; - /* Ensure the requestor has permissions over the target filesystem */ - if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT)) && !ns_capable(user_ns, CAP_SYS_ADMIN)) - return ERR_PTR(-EPERM); - return sget_userns(type, test, set, flags, user_ns, data); } @@ -1164,12 +1164,6 @@ struct dentry *mount_ns(struct file_system_type *fs_type, { struct super_block *sb; - /* Don't allow mounting unless the caller has CAP_SYS_ADMIN - * over the namespace. - */ - if (!(flags & SB_KERNMOUNT) && !ns_capable(user_ns, CAP_SYS_ADMIN)) - return ERR_PTR(-EPERM); - sb = sget_userns(fs_type, ns_test_super, ns_set_super, flags, user_ns, ns); if (IS_ERR(sb)) -- cgit v1.2.3-59-g8ed1b