On Sat, Oct 03, 2026 at 07:34:15PM +0900, [email protected] wrote: > From: Sung Byeongchan <[email protected]> > > SafeSetID policies constrain the ID transitions available to a task for > each source ID. id_permitted_for_cred() always builds that source key > from the old real UID, even when it is checking a GID transition. If the > real UID and real GID differ, the policy attached to the real GID is > therefore missed and the lookup can return the unconstrained default. > > On current mainline, a test task with real UID 1000, real GID 2000 and > only CAP_SETGID obtained non-allowlisted GID 2002 despite a 2000:2001 GID > policy. The bypass reproduced for setgid(), setegid(), setregid(), > setresgid(), setfsgid() and setgroups() across three clean QEMU boots, > and enabled access to a synthetic group-protected resource. This shows > a SafeSetID GID policy bypass and group privilege expansion; it does not > show direct UID 0 elevation or a universal local privilege escalation. > > Build the source key from the old real UID for UID policy checks and the > old real GID for GID policy checks. In three fixed-kernel boots, all > tested non-allowlisted transitions were blocked while the allowed target, > existing-ID, no-policy and UID-policy controls, and the existing SafeSetID > selftest continued to pass. > > Fixes: 5294bac97e12 ("LSM: SafeSetID: Add GID security policy handling") > Cc: [email protected] > Assisted-by: OpenAI Codex > Signed-off-by: Sung Byeongchan <[email protected]>
Seems obviously correct. Thanks for the find and the fix. Reviewed-by: Serge Hallyn <[email protected]> > --- > security/safesetid/lsm.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c > index d5fb949050dd8..18124fc499dbc 100644 > --- a/security/safesetid/lsm.c > +++ b/security/safesetid/lsm.c > @@ -148,13 +148,16 @@ static int safesetid_security_capable(const struct cred > *cred, > static bool id_permitted_for_cred(const struct cred *old, kid_t new_id, enum > setid_type new_type) > { > bool permitted; > + kid_t source_id; > > /* If our old creds already had this ID in it, it's fine. */ > if (new_type == UID) { > + source_id.uid = old->uid; > if (uid_eq(new_id.uid, old->uid) || uid_eq(new_id.uid, > old->euid) || > uid_eq(new_id.uid, old->suid)) > return true; > } else if (new_type == GID){ > + source_id.gid = old->gid; > if (gid_eq(new_id.gid, old->gid) || gid_eq(new_id.gid, > old->egid) || > gid_eq(new_id.gid, old->sgid)) > return true; > @@ -162,11 +165,10 @@ static bool id_permitted_for_cred(const struct cred > *old, kid_t new_id, enum set > return false; > > /* > - * Transitions to new UIDs require a check against the policy of the old > - * RUID. > + * Transitions require a check against the policy of the old real ID. > */ > permitted = > - setid_policy_lookup((kid_t){.uid = old->uid}, new_id, new_type) != > SIDPOL_CONSTRAINED; > + setid_policy_lookup(source_id, new_id, new_type) != > SIDPOL_CONSTRAINED; > > if (!permitted) { > if (new_type == UID) { > -- > 2.43.0
