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capabilities: factor out cap_bprm_set_creds privileged root

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Factor out the case of privileged root from the function
cap_bprm_set_creds() to make the latter easier to read and analyse.

Suggested-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Acked-by: Kees Cook <keescook@chromium.org>
Okay-ished-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
This commit is contained in:
Richard Guy Briggs 2017-10-11 20:57:05 -04:00 committed by James Morris
parent 33957a104c
commit db1a8922cf
1 changed files with 48 additions and 28 deletions
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76
security/commoncap.c
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@ -695,6 +695,52 @@ out:
return rc;
}
/*
* handle_privileged_root - Handle case of privileged root
* @bprm: The execution parameters, including the proposed creds
* @has_fcap: Are any file capabilities set?
* @effective: Do we have effective root privilege?
* @root_uid: This namespace' root UID WRT initial USER namespace
*
* Handle the case where root is privileged and hasn't been neutered by
* SECURE_NOROOT. If file capabilities are set, they won't be combined with
* set UID root and nothing is changed. If we are root, cap_permitted is
* updated. If we have become set UID root, the effective bit is set.
*/
static void handle_privileged_root(struct linux_binprm *bprm, bool has_cap,
bool *effective, kuid_t root_uid)
{
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
if (issecure(SECURE_NOROOT))
return;
/*
* 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 && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
warn_setuid_and_fcaps_mixed(bprm->filename);
return;
}
/*
* To support inheritance of root-permissions and suid-root
* executables under compatibility mode, we override the
* capability sets for the file.
*/
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 only the real uid is 0, we do not set the effective bit.
*/
if (uid_eq(new->euid, root_uid))
*effective = true;
}
/**
* cap_bprm_set_creds - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
@ -707,46 +753,20 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
{
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
bool effective, has_cap = false, is_setid;
bool effective = false, has_cap = false, is_setid;
int ret;
kuid_t root_uid;
if (WARN_ON(!cap_ambient_invariant_ok(old)))
return -EPERM;
effective = false;
ret = get_file_caps(bprm, &effective, &has_cap);
if (ret < 0)
return ret;
root_uid = make_kuid(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 && !uid_eq(new->uid, root_uid) && uid_eq(new->euid, root_uid)) {
warn_setuid_and_fcaps_mixed(bprm->filename);
goto skip;
}
/*
* To support inheritance of root-permissions and suid-root
* executables under compatibility mode, we override the
* capability sets for the file.
*
* If only the real uid is 0, we do not set the effective bit.
*/
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 (uid_eq(new->euid, root_uid))
effective = true;
}
skip:
handle_privileged_root(bprm, has_cap, &effective, root_uid);
/* if we have fs caps, clear dangerous personality flags */
if (!cap_issubset(new->cap_permitted, old->cap_permitted))