[d-kernel] [PATCH] AltHa: handle setcap binaries in the same way as setuid ones

[Vladimir D. Seleznev]

altha.nosuid facility controls what binaries can raise user privilleges.
Prior to this commit it only handled setuid binaries, but it was still
possible to raise privilleges via setcaps. Now it handles both setuid
and setcap binaries.

Signed-off-by: Vladimir D. Seleznev <vseleznv на altlinux.org>
---
 Documentation/admin-guide/LSM/AltHa.rst |  6 ++--
 security/altha/altha_lsm.c              | 48 ++++++++++++++++++++-----
 2 files changed, 43 insertions(+), 11 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..4f6b309445c0 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 +238,19 @@ 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;
+	char *setuidcap_srt = "setuid";
 	/* when it's not a shebang issued script interpreter */
 	if (rstrscript_enabled && bprm->executable == bprm->interpreter) {
 		char *path_p;
@@ -267,11 +277,30 @@ 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;
+		int is_setuid = 0, is_setcap = 0;
+		uid_t cur_uid, cur_euid;
+
+		is_setuid = !uid_eq(bprm->cred->uid, bprm->cred->euid);
+
+		if (!is_setuid) {
+			cur_euid = from_kuid(bprm->cred->user_ns, bprm->cred->euid);
+			if (cur_euid != (uid_t) 0)
+				is_setcap = has_any_caps(bprm->cred);
+		}
+
+		/*
+		 * If no suid but it has any caps, change message string from
+		 * setuid to setcap.
+		 */
+		if (is_setcap)
+			setuidcap_srt = "setcap";
+
+		/* If no suid and no caps detected, exit. */
+		if (!is_setuid && !is_setcap)
+			return 0;
 
 		path_buffer = kmalloc(PATH_MAX, GFP_KERNEL);
 		if (!path_buffer)
@@ -283,8 +312,8 @@ 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, setuidcap_srt, cur_uid);
 				up_read(&nosuid_exceptions_sem);
 				kfree(path_buffer);
 				return 0;
@@ -292,9 +321,12 @@ 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, setuidcap_srt, cur_uid);
+		if (is_setuid)
+			bprm->cred->euid = bprm->cred->uid;
+		cap_clear(bprm->cred->cap_permitted);
+		cap_clear(bprm->cred->cap_effective);
 		kfree(path_buffer);
 	}
 	return 0;
-- 
2.33.3