Re: [PATCH 22/43] userns: Convert capabilities related permsion checks

Serge E. Hallyn
2012-04-18T18:50:11Z

Quoting Eric W. Beiderman (ebiederm@xmission.com):
> From: Eric W. Biederman <ebiederm@xmission.com>
>
> - Use uid_eq when comparing kuids
> Use gid_eq when comparing kgids
> - Use __make_kuid(user_ns, 0) to talk about the user_namespace root uid
> Use __make_kgid(user_ns, 0) to talk about the user_namespace root gid
>
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

though, nit,

> ---
> fs/open.c | 3 ++-
> security/commoncap.c | 43 ++++++++++++++++++++++++++++---------------
> 2 files changed, 30 insertions(+), 16 deletions(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index 5720854..92335f6 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -316,7 +316,8 @@ SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
>
> if (!issecure(SECURE_NO_SETUID_FIXUP)) {
> /* Clear the capabilities if we switch to a non-root user */
> - if (override_cred->uid)
> + kuid_t root_uid = make_kuid(override_cred->user_ns, 0);
> + if (!uid_eq(override_cred->uid, root_uid))
> cap_clear(override_cred->cap_effective);
> else
> override_cred->cap_effective =
> diff --git a/security/commoncap.c b/security/commoncap.c
> index dbd465a..9bf8df8 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -472,19 +472,24 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
> struct cred *new = bprm->cred;
> bool effective, has_cap = false;
> int ret;
> + kuid_t root_uid;
> + kgid_t root_gid;

the root_gid is assigned but never used.

>
> effective = false;
> ret = get_file_caps(bprm, &effective, &has_cap);
> if (ret < 0)
> return ret;
>
> + root_uid = make_kuid(new->user_ns, 0);
> + root_gid = make_kgid(new->user_ns, 0);
> +
> if (!issecure(SECURE_NOROOT)) {
> /*
> * If the legacy file capability is set, then don't set privs
> * for a setuid root binary run by a non-root user. Do set it
> * for a root user just to cause least surprise to an admin.
> */
> - if (has_cap && new->uid != 0 && new->euid == 0) {
> + if (has_cap && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
> warn_setuid_and_fcaps_mixed(bprm->filename);
> goto skip;
> }
> @@ -495,12 +500,12 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
> *
> * If only the real uid is 0, we do not set the effective bit.
> */
> - if (new->euid == 0 || new->uid == 0) {
> + if (uid_eq(new->euid, root_uid) || uid_eq(new->uid, root_uid)) {
> /* pP' = (cap_bset & ~0) | (pI & ~0) */
> new->cap_permitted = cap_combine(old->cap_bset,
> old->cap_inheritable);
> }
> - if (new->euid == 0)
> + if (uid_eq(new->euid, root_uid))
> effective = true;
> }
> skip:
> @@ -508,8 +513,8 @@ skip:
> /* Don't let someone trace a set[ug]id/setpcap binary with the revised
> * credentials unless they have the appropriate permit
> */
> - if ((new->euid != old->uid ||
> - new->egid != old->gid ||
> + if ((!uid_eq(new->euid, old->uid) ||
> + !gid_eq(new->egid, old->gid) ||
> !cap_issubset(new->cap_permitted, old->cap_permitted)) &&
> bprm->unsafe & ~LSM_UNSAFE_PTRACE_CAP) {
> /* downgrade; they get no more than they had, and maybe less */
> @@ -544,7 +549,7 @@ skip:
> */
> if (!cap_isclear(new->cap_effective)) {
> if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
> - new->euid != 0 || new->uid != 0 ||
> + !uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
> issecure(SECURE_NOROOT)) {
> ret = audit_log_bprm_fcaps(bprm, new, old);
> if (ret < 0)
> @@ -569,16 +574,17 @@ skip:
> int cap_bprm_secureexec(struct linux_binprm *bprm)
> {
> const struct cred *cred = current_cred();
> + kuid_t root_uid = make_kuid(cred->user_ns, 0);
>
> - if (cred->uid != 0) {
> + if (!uid_eq(cred->uid, root_uid)) {
> if (bprm->cap_effective)
> return 1;
> if (!cap_isclear(cred->cap_permitted))
> return 1;
> }
>
> - return (cred->euid != cred->uid ||
> - cred->egid != cred->gid);
> + return (!uid_eq(cred->euid, cred->uid) ||
> + !gid_eq(cred->egid, cred->gid));
> }
>
> /**
> @@ -668,15 +674,21 @@ int cap_inode_removexattr(struct dentry *dentry, const char *name)
> */
> static inline void cap_emulate_setxuid(struct cred *new, const struct cred *old)
> {
> - if ((old->uid == 0 || old->euid == 0 || old->suid == 0) &&
> - (new->uid != 0 && new->euid != 0 && new->suid != 0) &&
> + kuid_t root_uid = make_kuid(old->user_ns, 0);
> +
> + if ((uid_eq(old->uid, root_uid) ||
> + uid_eq(old->euid, root_uid) ||
> + uid_eq(old->suid, root_uid)) &&
> + (!uid_eq(new->uid, root_uid) &&
> + !uid_eq(new->euid, root_uid) &&
> + !uid_eq(new->suid, root_uid)) &&
> !issecure(SECURE_KEEP_CAPS)) {
> cap_clear(new->cap_permitted);
> cap_clear(new->cap_effective);
> }
> - if (old->euid == 0 && new->euid != 0)
> + if (uid_eq(old->euid, root_uid) && !uid_eq(new->euid, root_uid))
> cap_clear(new->cap_effective);
> - if (old->euid != 0 && new->euid == 0)
> + if (!uid_eq(old->euid, root_uid) && uid_eq(new->euid, root_uid))
> new->cap_effective = new->cap_permitted;
> }
>
> @@ -709,11 +721,12 @@ int cap_task_fix_setuid(struct cred *new, const struct cred *old, int flags)
> * if not, we might be a bit too harsh here.
> */
> if (!issecure(SECURE_NO_SETUID_FIXUP)) {
> - if (old->fsuid == 0 && new->fsuid != 0)
> + kuid_t root_uid = make_kuid(old->user_ns, 0);
> + if (uid_eq(old->fsuid, root_uid) && !uid_eq(new->fsuid, root_uid))
> new->cap_effective =
> cap_drop_fs_set(new->cap_effective);
>
> - if (old->fsuid != 0 && new->fsuid == 0)
> + if (!uid_eq(old->fsuid, root_uid) && uid_eq(new->fsuid, root_uid))
> new->cap_effective =
> cap_raise_fs_set(new->cap_effective,
> new->cap_permitted);
> --
> 1.7.2.5
>
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