Messages in this thread | | | Date | Thu, 27 Jan 2022 08:42:26 -0500 | Subject | Re: [RFC PATCH] selinux: split no transition execve check | From | Chris PeBenito <> |
| |
On 1/26/22 17:51, Paul Moore wrote: > On Tue, Jan 25, 2022 at 9:59 AM Christian Göttsche > <cgzones@googlemail.com> wrote: >> >> In case a setuid or setgid binary is mislabeled with a generic context, >> either via a policy mistake or a move by the distribution package, >> executing it will be checked by the file permission execute_no_trans on >> the generic file context (e.g. bin_t). The setuid(2)/setgid(2) syscall >> within will then be checked against the unchanged caller process >> context, which might have been granted the capability permission setuid/ >> setgid to initially drop privileges. To avoid that scenario split the >> execute_no_trans permission in case of a setuid/setgid binary into a new >> permission execute_sxid_no_trans. >> >> For backward compatibility this behavior is contained in a new policy >> capability. >> >> Signed-off-by: Christian Göttsche <cgzones@googlemail.com> >> --- >> security/selinux/hooks.c | 9 ++++++++- >> security/selinux/include/classmap.h | 2 +- >> security/selinux/include/policycap.h | 1 + >> security/selinux/include/policycap_names.h | 3 ++- >> security/selinux/include/security.h | 8 ++++++++ >> 5 files changed, 20 insertions(+), 3 deletions(-) > > Adding the refpolicy list to this thread as their opinion seems > particularly relevant to this discussion. > > FWIW, this looks reasonable to me but I would like to hear what others > have to say.
I think this a band-aid to cover up the real problem, which is the mislabeled files.
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c >> index 5b6895e4fc29..b825fee39a70 100644 >> --- a/security/selinux/hooks.c >> +++ b/security/selinux/hooks.c >> @@ -2348,9 +2348,16 @@ static int selinux_bprm_creds_for_exec(struct linux_binprm *bprm) >> ad.u.file = bprm->file; >> >> if (new_tsec->sid == old_tsec->sid) { >> + u32 perm; >> + >> + if (selinux_policycap_execute_sxid_no_trans() && is_sxid(inode->i_mode)) >> + perm = FILE__EXECUTE_SXID_NO_TRANS; >> + else >> + perm = FILE__EXECUTE_NO_TRANS; >> + >> rc = avc_has_perm(&selinux_state, >> old_tsec->sid, isec->sid, >> - SECCLASS_FILE, FILE__EXECUTE_NO_TRANS, &ad); >> + SECCLASS_FILE, perm, &ad); >> if (rc) >> return rc; >> } else { >> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h >> index 35aac62a662e..53a1eeeb86fb 100644 >> --- a/security/selinux/include/classmap.h >> +++ b/security/selinux/include/classmap.h >> @@ -65,7 +65,7 @@ struct security_class_mapping secclass_map[] = { >> "quotaget", "watch", NULL } }, >> { "file", >> { COMMON_FILE_PERMS, >> - "execute_no_trans", "entrypoint", NULL } }, >> + "execute_no_trans", "entrypoint", "execute_sxid_no_trans", NULL } }, >> { "dir", >> { COMMON_FILE_PERMS, "add_name", "remove_name", >> "reparent", "search", "rmdir", NULL } }, >> diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h >> index 2ec038efbb03..23929dc3e1db 100644 >> --- a/security/selinux/include/policycap.h >> +++ b/security/selinux/include/policycap.h >> @@ -11,6 +11,7 @@ enum { >> POLICYDB_CAPABILITY_CGROUPSECLABEL, >> POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION, >> POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS, >> + POLICYDB_CAPABILITY_EXECUTE_SXID_NO_TRANS, >> __POLICYDB_CAPABILITY_MAX >> }; >> #define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1) >> diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h >> index b89289f092c9..4c014c2cf352 100644 >> --- a/security/selinux/include/policycap_names.h >> +++ b/security/selinux/include/policycap_names.h >> @@ -12,7 +12,8 @@ const char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = { >> "always_check_network", >> "cgroup_seclabel", >> "nnp_nosuid_transition", >> - "genfs_seclabel_symlinks" >> + "genfs_seclabel_symlinks", >> + "execute_sxid_no_trans", >> }; >> >> #endif /* _SELINUX_POLICYCAP_NAMES_H_ */ >> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h >> index ac0ece01305a..ab95241b6b7b 100644 >> --- a/security/selinux/include/security.h >> +++ b/security/selinux/include/security.h >> @@ -219,6 +219,14 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void) >> return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]); >> } >> >> +static inline bool selinux_policycap_execute_sxid_no_trans(void) >> +{ >> + struct selinux_state *state = &selinux_state; >> + >> + return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_EXECUTE_SXID_NO_TRANS]); >> +} >> + >> + >> struct selinux_policy_convert_data; >> >> struct selinux_load_state { >> -- >> 2.34.1 >> > >
-- Chris PeBenito
| |