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| author | Seth Forshee <seth.forshee@canonical.com> | 2015-09-23 15:16:04 -0500 |
|---|---|---|
| committer | Eric W. Biederman <ebiederm@xmission.com> | 2016-06-24 10:40:31 -0500 |
| commit | d07b846f6200454c50d791796edb82660192513d (patch) | |
| tree | 0addc4233c4e08fc7ca69511761bbd2c7402c1de | |
| parent | cc50a07a247e17db76b1f0b0ca06652556e04fa3 (diff) | |
| download | lwn-d07b846f6200454c50d791796edb82660192513d.tar.gz lwn-d07b846f6200454c50d791796edb82660192513d.zip | |
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, current_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.
--EWB Replaced in_userns with the simpler current_in_userns.
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
| -rw-r--r-- | include/linux/user_namespace.h | 6 | ||||
| -rw-r--r-- | kernel/user_namespace.c | 14 | ||||
| -rw-r--r-- | security/commoncap.c | 2 |
3 files changed, 22 insertions, 0 deletions
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index 8297e5b341d8..9217169c64cb 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -72,6 +72,7 @@ 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 int proc_setgroups_show(struct seq_file *m, void *v); extern bool userns_may_setgroups(const struct user_namespace *ns); +extern bool current_in_userns(const struct user_namespace *target_ns); #else static inline struct user_namespace *get_user_ns(struct user_namespace *ns) @@ -100,6 +101,11 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) { return true; } + +static inline bool current_in_userns(const struct user_namespace *target_ns) +{ + return true; +} #endif #endif /* _LINUX_USER_H */ diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 9bafc211930c..68f594212759 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -938,6 +938,20 @@ bool userns_may_setgroups(const struct user_namespace *ns) return allowed; } +/* + * Returns true if @ns is the same namespace as or a descendant of + * @target_ns. + */ +bool current_in_userns(const struct user_namespace *target_ns) +{ + struct user_namespace *ns; + for (ns = current_user_ns(); ns; ns = ns->parent) { + if (ns == target_ns) + return true; + } + return false; +} + static inline struct user_namespace *to_user_ns(struct ns_common *ns) { return container_of(ns, struct user_namespace, ns); diff --git a/security/commoncap.c b/security/commoncap.c index e7fadde737f4..e109e6dac858 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -455,6 +455,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) return 0; + if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns)) + return 0; rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); if (rc < 0) { |