nspawn: Map all seccomp filters to capabilities

This change makes it so all seccomp filters are mapped
to the appropriate capability and are only added if that
capability was not requested when running the container.

This unbreaks the remaining use cases broken by the
addition of seccomp filters without respecting requested
capabilities.

Co-Authored-By: Clif Houck <me@clifhouck.com>
[zj: - adapt to our coding style, make struct anonymous]

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c
index 8ce5fbeb629f6b25db1bd7cd0c297bf21c0e5067..8833704ab79839cc675ba59941735251baf8aa6b 100644 (file)
--- a/src/nspawn/nspawn.c
+++ b/src/nspawn/nspawn.c
@@ -2567,19 +2567,19 @@ static int setup_ipvlan(pid_t pid) {
 static int setup_seccomp(void) {
 
 #ifdef HAVE_SECCOMP
-        static const int blacklist[] = {
-                SCMP_SYS(kexec_load),
-                SCMP_SYS(open_by_handle_at),
-                SCMP_SYS(iopl),
-                SCMP_SYS(ioperm),
-                SCMP_SYS(swapon),
-                SCMP_SYS(swapoff),
-        };
-
-        static const int kmod_blacklist[] = {
-                SCMP_SYS(init_module),
-                SCMP_SYS(finit_module),
-                SCMP_SYS(delete_module),
+        static const struct {
+                uint64_t capability;
+                int syscall_num;
+        } blacklist[] = {
+                { CAP_SYS_RAWIO,  SCMP_SYS(iopl)},
+                { CAP_SYS_RAWIO,  SCMP_SYS(ioperm)},
+                { CAP_SYS_BOOT,   SCMP_SYS(kexec_load)},
+                { CAP_SYS_ADMIN,  SCMP_SYS(swapon)},
+                { CAP_SYS_ADMIN,  SCMP_SYS(swapoff)},
+                { CAP_SYS_ADMIN,  SCMP_SYS(open_by_handle_at)},
+                { CAP_SYS_MODULE, SCMP_SYS(init_module)},
+                { CAP_SYS_MODULE, SCMP_SYS(finit_module)},
+                { CAP_SYS_MODULE, SCMP_SYS(delete_module)},
         };
 
         scmp_filter_ctx seccomp;
@@ -2597,7 +2597,10 @@ static int setup_seccomp(void) {
         }
 
         for (i = 0; i < ELEMENTSOF(blacklist); i++) {
-                r = seccomp_rule_add(seccomp, SCMP_ACT_ERRNO(EPERM), blacklist[i], 0);
+                if (arg_retain & (1ULL << blacklist[i].capability))
+                        continue;
+
+                r = seccomp_rule_add(seccomp, SCMP_ACT_ERRNO(EPERM), blacklist[i].syscall_num, 0);
                 if (r == -EFAULT)
                         continue; /* unknown syscall */
                 if (r < 0) {
@@ -2606,19 +2609,6 @@ static int setup_seccomp(void) {
                 }
         }
 
-        /* If the CAP_SYS_MODULE capability is not requested then
-         * we'll block the kmod syscalls too */
-        if (!(arg_retain & (1ULL << CAP_SYS_MODULE))) {
-                for (i = 0; i < ELEMENTSOF(kmod_blacklist); i++) {
-                        r = seccomp_rule_add(seccomp, SCMP_ACT_ERRNO(EPERM), kmod_blacklist[i], 0);
-                        if (r == -EFAULT)
-                                continue; /* unknown syscall */
-                        if (r < 0) {
-                                log_error_errno(r, "Failed to block syscall: %m");
-                                goto finish;
-                        }
-                }
-        }
 
         /*
            Audit is broken in containers, much of the userspace audit