Re: [PATCH V3 05/10] capabilities: use intuitive names for id changes
On Wed, Aug 23, 2017 at 3:12 AM, Richard Guy Briggs <rgb(a)redhat.com> wrote:
Introduce a number of inlines to make the use of the negation of
uid_eq() easier to read and analyse.
Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com>
---
security/commoncap.c | 26 +++++++++++++++++++++-----
1 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/security/commoncap.c b/security/commoncap.c
index 36c38a1..1af7dec 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -483,6 +483,15 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective,
bool *has_f
static inline bool root_privileged(void) { return !issecure(SECURE_NOROOT); }
+static inline bool is_real(kuid_t uid, struct cred *cred)
+{ return uid_eq(cred->uid, uid); }
OK I guess, but this just seems like a way to obfuscate the code a bit
and save typing "->uid".
+
+static inline bool is_eff(kuid_t uid, struct cred *cred)
+{ return uid_eq(cred->euid, uid); }
Ditto.
+
+static inline bool is_suid(kuid_t uid, struct cred *cred)
+{ return !is_real(uid, cred) && is_eff(uid, cred); }
Please no. This is IMO insane. You're hiding really weird,
nonintuitive logic in an oddly named helper.
Also, this is going to cause massive confusion and severe bugs: given
the same, the only remotely sensible guess as to what this function
does is uid_eq(cred->suid, uid). So NAK to this.
+
void handle_privileged_root(struct linux_binprm *bprm, bool has_fcap, bool *effective,
kuid_t root_uid)
{
const struct cred *old = current_cred();
@@ -493,7 +502,7 @@ void handle_privileged_root(struct linux_binprm *bprm, bool has_fcap,
bool *effe
* 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_fcap && !uid_eq(new->uid, root_uid) &&
uid_eq(new->euid, root_uid)) {
+ if (has_fcap && is_suid(root_uid, new)) {
e.g. this. The logic used to be obviously slightly dicey. Now it
looks sane but doesn't do what you'd naively expect it to do, which is
far worse.
@@ -519,6 +528,13 @@ void handle_privileged_root(struct linux_binprm
*bprm, bool has_fcap, bool *effe
!cap_issubset(cred->cap_##target, cred->cap_##source)
#define cap_full(field, cred) \
cap_issubset(CAP_FULL_SET, cred->cap_##field)
+
+static inline bool is_setuid(struct cred *new, const struct cred *old)
+{ return !uid_eq(new->euid, old->uid); }
+
+static inline bool is_setgid(struct cred *new, const struct cred *old)
+{ return !gid_eq(new->egid, old->gid); }
Please don't. This logic is fragile, and these helpers are pretending
it's not fragile even though it's still fragile.