Commit a8c473e9 authored by Seth Forshee's avatar Seth Forshee Committed by Eric W. Biederman

fs: Limit file caps to the user namespace of the super block

Capability sets attached to files must be ignored except in the
user namespaces where the mounter is privileged, i.e. s_user_ns
and its descendants. Otherwise a vector exists for gaining
privileges in namespaces where a user is not already privileged.

Add a new helper function, in_user_ns(), to test whether a user
namespace is the same as or a descendant of another namespace.
Use this helper to determine whether a file's capability set
should be applied to the caps constructed during exec.
Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatarSeth Forshee <seth.forshee@canonical.com>
Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent 4aceccd6
...@@ -72,6 +72,8 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, ...@@ -72,6 +72,8 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t,
extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *); extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *);
extern int proc_setgroups_show(struct seq_file *m, void *v); extern int proc_setgroups_show(struct seq_file *m, void *v);
extern bool userns_may_setgroups(const struct user_namespace *ns); extern bool userns_may_setgroups(const struct user_namespace *ns);
extern bool in_userns(const struct user_namespace *ns,
const struct user_namespace *target_ns);
#else #else
static inline struct user_namespace *get_user_ns(struct user_namespace *ns) static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
...@@ -100,6 +102,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) ...@@ -100,6 +102,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns)
{ {
return true; return true;
} }
static inline bool in_userns(const struct user_namespace *ns,
const struct user_namespace *target_ns)
{
return true;
}
#endif #endif
#endif /* _LINUX_USER_H */ #endif /* _LINUX_USER_H */
...@@ -945,6 +945,20 @@ bool userns_may_setgroups(const struct user_namespace *ns) ...@@ -945,6 +945,20 @@ bool userns_may_setgroups(const struct user_namespace *ns)
return allowed; return allowed;
} }
/*
* Returns true if @ns is the same namespace as or a descendant of
* @target_ns.
*/
bool in_userns(const struct user_namespace *ns,
const struct user_namespace *target_ns)
{
for (; ns; ns = ns->parent) {
if (ns == target_ns)
return true;
}
return false;
}
static inline struct user_namespace *to_user_ns(struct ns_common *ns) static inline struct user_namespace *to_user_ns(struct ns_common *ns)
{ {
return container_of(ns, struct user_namespace, ns); return container_of(ns, struct user_namespace, ns);
......
...@@ -450,6 +450,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c ...@@ -450,6 +450,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
return 0; return 0;
if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns))
return 0;
rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
if (rc < 0) { if (rc < 0) {
......
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