From 8cc497e735104080f6830a8f468b2724ae372990 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Wed, 3 Apr 2019 13:11:00 +0200
Subject: [PATCH] seccomp: rework how the S[UG]ID filter is installed
If we know that a syscall is undefined on the given architecture, don't
even try to add it.
Try to install the filter even if some syscalls fail. Also use a helper
function to make the whole a bit less magic.
This allows the S[UG]ID test to pass on arm64.
(cherry picked from commit da4dc9a6748797e804b6bc92ad513d509abf581c)
Resolves: #1860374
---
src/shared/seccomp-util.c | 244 +++++++++++++++++++++-----------------
1 file changed, 138 insertions(+), 106 deletions(-)
diff --git a/src/shared/seccomp-util.c b/src/shared/seccomp-util.c
index fd46b9f88d..d91fb4e269 100644
--- a/src/shared/seccomp-util.c
+++ b/src/shared/seccomp-util.c
@@ -1750,9 +1750,139 @@ int seccomp_lock_personality(unsigned long personality) {
return 0;
}
+static int seccomp_restrict_sxid(scmp_filter_ctx seccomp, mode_t m) {
+ /* Checks the mode_t parameter of the following system calls:
+ *
+ * → chmod() + fchmod() + fchmodat()
+ * → open() + creat() + openat()
+ * → mkdir() + mkdirat()
+ * → mknod() + mknodat()
+ *
+ * Returns error if *everything* failed, and 0 otherwise.
+ */
+ int r = 0;
+ bool any = false;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for chmod: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for fchmod: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for fchmodat: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for mkdir: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for mkdirat: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for mknod: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for mknodat: %m");
+ else
+ any = true;
+
+#if SCMP_SYS(open) > 0
+ 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)
+ log_debug_errno(r, "Failed to add filter for open: %m");
+ else
+ any = true;
+#endif
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for openat: %m");
+ else
+ any = true;
+
+ 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)
+ log_debug_errno(r, "Failed to add filter for creat: %m");
+ else
+ any = true;
+
+ return any ? 0 : r;
+}
+
int seccomp_restrict_suid_sgid(void) {
uint32_t arch;
- int r;
+ int r, k;
SECCOMP_FOREACH_LOCAL_ARCH(arch) {
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
@@ -1761,114 +1891,16 @@ int seccomp_restrict_suid_sgid(void) {
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_restrict_sxid(seccomp, S_ISUID);
+ if (r < 0)
+ log_debug_errno(r, "Failed to add suid rule for architecture %s, ignoring: %m", seccomp_arch_to_string(arch));
- 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;
+ k = seccomp_restrict_sxid(seccomp, S_ISGID);
+ if (k < 0)
+ log_debug_errno(r, "Failed to add sgid rule for architecture %s, ignoring: %m", seccomp_arch_to_string(arch));
- 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));
+ if (r < 0 && k < 0)
continue;
- }
r = seccomp_load(seccomp);
if (IN_SET(r, -EPERM, -EACCES))