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[77.10.144.44]) by smtp.gmail.com with ESMTPSA id y17sm6353141ejw.172.2022.01.25.06.59.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Jan 2022 06:59:37 -0800 (PST) From: =?utf-8?q?Christian_G=C3=B6ttsche?= To: selinux@vger.kernel.org Cc: Paul Moore , Stephen Smalley , Eric Paris , "David S. Miller" , Ondrej Mosnacek , Jeremy Kerr , Xiong Zhenwu , Tyler Hicks , linux-kernel@vger.kernel.org Subject: [RFC PATCH] selinux: split no transition execve check Date: Tue, 25 Jan 2022 15:59:27 +0100 Message-Id: <20220125145931.56831-1-cgzones@googlemail.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org 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 --- 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(-) 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 {