[d-kernel] [PATCH] AltHa: nosuid handles capabilities as well

[Vladimir D. Seleznev]

Signed-off-by: Vladimir D. Seleznev <vseleznv на altlinux.org>
---
 Documentation/admin-guide/LSM/AltHa.rst |  6 ++--
 security/altha/altha_lsm.c              | 37 ++++++++++++++++++++-----
 2 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/LSM/AltHa.rst b/Documentation/admin-guide/LSM/AltHa.rst
index be698709d3f0..beda40601c9e 100644
--- a/Documentation/admin-guide/LSM/AltHa.rst
+++ b/Documentation/admin-guide/LSM/AltHa.rst
@@ -3,7 +3,7 @@ AltHa
 ====
 
 AltHa is a Linux Security Module currently has three userspace hardening options:
-    * ignore SUID on binaries (with exceptions possible);
+    * ignore SUID and setcaps on binaries (with exceptions possible);
     * prevent running selected script interpreters in interactive mode;
     * disable open file unlinking in selected dirs.
     * enable kiosk mode
@@ -15,12 +15,12 @@ through sysctls in ``/proc/sys/kernel/altha``.
 
 NoSUID
 ============
-Modern Linux systems can be used with minimal (or even zero at least for OWL and ALT) usage of SUID programms, but in many cases in full-featured desktop or server systems there are plenty of them: uncounted and sometimes unnecessary. Privileged programms are always an attack surface, but mounting filesystems with ``nosuid`` flag doesn't provide enough granularity in SUID binaries management. This LSM module provides a single control point for all SUID binaries. When this submodule is enabled, SUID bits on all binaries except explicitly listed are system-wide ignored.
+Modern Linux systems can be used with minimal (or even zero at least for OWL and ALT) usage of SUID programms, but in many cases in full-featured desktop or server systems there are plenty of them: uncounted and sometimes unnecessary. Privileged programms are always an attack surface, but mounting filesystems with ``nosuid`` flag doesn't provide enough granularity in SUID binaries management. This LSM module provides a single control point for all SUID and setcap binaries. When this submodule is enabled, SUID and setcap bits on all binaries except explicitly listed are system-wide ignored.
 
 Sysctl parameters and defaults:
 
 * ``kernel.altha.nosuid.enabled = 0``, set to 1 to enable
-* ``kernel.altha.nosuid.exceptions =``, colon-separated list of enabled SUID binaries, for example: ``/bin/su:/usr/libexec/hasher-priv/hasher-priv``
+* ``kernel.altha.nosuid.exceptions =``, colon-separated list of enabled SUID and setcap binaries, for example: ``/bin/su:/usr/libexec/hasher-priv/hasher-priv``
 
 RestrScript
 ============
diff --git a/security/altha/altha_lsm.c b/security/altha/altha_lsm.c
index c670ad7ed458..5f0505a51644 100644
--- a/security/altha/altha_lsm.c
+++ b/security/altha/altha_lsm.c
@@ -11,6 +11,7 @@
 
 #include <linux/lsm_hooks.h>
 #include <linux/cred.h>
+#include <linux/capability.h>
 #include <linux/sysctl.h>
 #include <linux/binfmts.h>
 #include <linux/file.h>
@@ -237,10 +238,20 @@ int is_olock_dir(struct inode *inode)
 	return 0;
 }
 
+static int has_any_caps(struct cred *cred)
+{
+	return !cap_isclear(cred->cap_permitted) ||
+	       !cap_isclear(cred->cap_effective);
+
+	return 0;
+}
+
 /* Hooks */
 static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * fi)
 {
 	struct altha_list_struct *node;
+	int is_set_caps = 0;
+	char *set_uid_cap = "setuid";
 	/* when it's not a shebang issued script interpreter */
 	if (rstrscript_enabled && bprm->executable == bprm->interpreter) {
 		char *path_p;
@@ -267,11 +278,18 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f
 		up_read(&interpreters_sem);
 		kfree(path_buffer);
 	}
-	if (unlikely(nosuid_enabled &&
-		     !uid_eq(bprm->cred->uid, bprm->cred->euid))) {
+	if (nosuid_enabled) {
 		char *path_p;
 		char *path_buffer;
 		uid_t cur_uid;
+		uid_t cur_euid = from_kuid(bprm->cred->user_ns, bprm->cred->euid);
+		/* Check for any caps for non-superuser. */
+		if (cur_euid != (uid_t) 0
+		   && has_any_caps(bprm->cred)) {
+			is_set_caps = 1;
+			set_uid_cap = "setcap";
+		} else if (uid_eq(bprm->cred->uid, bprm->cred->euid))
+			return 0;
 
 		path_buffer = kmalloc(PATH_MAX, GFP_KERNEL);
 		if (!path_buffer)
@@ -283,8 +301,8 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f
 		list_for_each_entry(node, &nosuid_exceptions_list, list) {
 			if (strcmp(path_p, node->spath) == 0) {
 				pr_notice_ratelimited
-				    ("AltHa/NoSUID: %s permitted to setuid from %d\n",
-				     bprm->filename, cur_uid);
+				    ("AltHa/NoSUID: %s permitted to %s from %d\n",
+				     bprm->filename, set_uid_cap, cur_uid);
 				up_read(&nosuid_exceptions_sem);
 				kfree(path_buffer);
 				return 0;
@@ -292,9 +310,14 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f
 		}
 		up_read(&nosuid_exceptions_sem);
 		pr_notice_ratelimited
-		    ("AltHa/NoSUID: %s prevented to setuid from %d\n",
-		     bprm->filename, cur_uid);
-		bprm->cred->euid = bprm->cred->uid;
+		    ("AltHa/NoSUID: %s prevented to %s from %d\n",
+		     bprm->filename, set_uid_cap, cur_uid);
+		if (is_set_caps) {
+			cap_clear(bprm->cred->cap_inheritable);
+			cap_clear(bprm->cred->cap_permitted);
+			cap_clear(bprm->cred->cap_effective);
+		} else
+			bprm->cred->euid = bprm->cred->uid;
 		kfree(path_buffer);
 	}
 	return 0;
-- 
2.33.2