1) all call chains leading to sget_userns() pass through ->mount()
instances.
2) none of ->mount() instances is ever called directly - the only
call site is legacy_get_tree()
3) all remaining ->mount() instances end up calling sget_userns()
IOW, we might as well do the capability checks just before calling
->mount(). As for the arguments passed to mount_capable(),
in case of call chains to sget_userns() going through sget(),
we either don't call mount_capable() at all, or pass current_user_ns()
to it. The call chains going through mount_pseudo_xattr() don't
call mount_capable() at all (SB_KERNMOUNT in flags on those).
That could've been split into smaller steps (lifting the checks
into sget(), then callers of sget(), then all the way to the
entries of every ->mount() out there, then to the sole caller),
but that would be too much churn for little benefit...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
struct super_block *sb;
struct dentry *root;
+ if (!(fc->sb_flags & (SB_KERNMOUNT|SB_SUBMOUNT))) {
+ if (!mount_capable(fc->fs_type, current_user_ns()))
+ return -EPERM;
+ }
+
root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
fc->source, ctx->legacy_data);
if (IS_ERR(root))
struct mount;
struct shrink_control;
struct fs_context;
+struct user_namespace;
/*
* block_dev.c
extern int reconfigure_super(struct fs_context *);
extern bool trylock_super(struct super_block *sb);
extern struct super_block *user_get_super(dev_t);
+extern bool mount_capable(struct file_system_type *, struct user_namespace *);
/*
* open.c
struct super_block *old;
int err;
- if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT))) {
- if (!mount_capable(type, user_ns))
- return ERR_PTR(-EPERM);
- }
retry:
spin_lock(&sb_lock);
if (test) {