From 5a62c0daff82e8343d24f98e1761d27bf8015782 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 20 Mar 2019 19:00:28 +0100
Subject: [PATCH] seccomp: introduce seccomp_restrict_suid_sgid() for blocking
chmod() for suid/sgid files
(cherry picked from commit 3c27973b13724ede05a06a5d346a569794cda433)
Related: #1687512
---
src/shared/seccomp-util.c | 132 ++++++++++++++++++++++++++++++++++++++
src/shared/seccomp-util.h | 1 +
2 files changed, 133 insertions(+)
diff --git a/src/shared/seccomp-util.c b/src/shared/seccomp-util.c
index 92910acf0e..fd46b9f88d 100644
--- a/src/shared/seccomp-util.c
+++ b/src/shared/seccomp-util.c
@@ -1,12 +1,14 @@
/* SPDX-License-Identifier: LGPL-2.1+ */
#include <errno.h>
+#include <fcntl.h>
#include <linux/seccomp.h>
#include <seccomp.h>
#include <stddef.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/shm.h>
+#include <sys/stat.h>
#include "af-list.h"
#include "alloc-util.h"
@@ -1747,3 +1749,133 @@ int seccomp_lock_personality(unsigned long personality) {
return 0;
}
+
+int seccomp_restrict_suid_sgid(void) {
+ uint32_t arch;
+ int r;
+
+ SECCOMP_FOREACH_LOCAL_ARCH(arch) {
+ _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
+
+ r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
+ if (r < 0)
+ return r;
+
+ /* Checks the mode_t parameter of the following system calls:
+ *
+ * → chmod() + fchmod() + fchmodat()
+ * → open() + creat() + openat()
+ * → mkdir() + mkdirat()
+ * → mknod() + mknodat()
+ */
+
+ for (unsigned bit = 0; bit < 2; bit ++) {
+ /* Block S_ISUID in the first iteration, S_ISGID in the second */
+ mode_t m = bit == 0 ? S_ISUID : S_ISGID;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(chmod),
+ 1,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(fchmod),
+ 1,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(fchmodat),
+ 1,
+ SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(mkdir),
+ 1,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(mkdirat),
+ 1,
+ SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(mknod),
+ 1,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(mknodat),
+ 1,
+ SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(open),
+ 2,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, O_CREAT, O_CREAT),
+ SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(openat),
+ 2,
+ SCMP_A2(SCMP_CMP_MASKED_EQ, O_CREAT, O_CREAT),
+ SCMP_A3(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+
+ r = seccomp_rule_add_exact(
+ seccomp,
+ SCMP_ACT_ERRNO(EPERM),
+ SCMP_SYS(creat),
+ 1,
+ SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+ if (r < 0)
+ break;
+ }
+ if (r < 0) {
+ log_debug_errno(r, "Failed to add suid/sgid rule for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
+ continue;
+ }
+
+ r = seccomp_load(seccomp);
+ if (IN_SET(r, -EPERM, -EACCES))
+ return r;
+ if (r < 0)
+ log_debug_errno(r, "Failed to apply suid/sgid restrictions for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
+ }
+
+ return 0;
+}
diff --git a/src/shared/seccomp-util.h b/src/shared/seccomp-util.h
index d8a36c4e21..602f092255 100644
--- a/src/shared/seccomp-util.h
+++ b/src/shared/seccomp-util.h
@@ -85,6 +85,7 @@ int seccomp_restrict_address_families(Set *address_families, bool whitelist);
int seccomp_restrict_realtime(void);
int seccomp_memory_deny_write_execute(void);
int seccomp_lock_personality(unsigned long personality);
+int seccomp_restrict_suid_sgid(void);
extern const uint32_t seccomp_local_archs[];