From 5a62c0daff82e8343d24f98e1761d27bf8015782 Mon Sep 17 00:00:00 2001 From: Lennart Poettering 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 +#include #include #include #include #include #include #include +#include #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[];