Merge tag 'seccomp-v5.17-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull seccomp fixes from Kees Cook:
"This fixes a corner case of fatal SIGSYS being ignored since v5.15.
Along with the signal fix is a change to seccomp so that seeing
another syscall after a fatal filter result will cause seccomp to kill
the process harder.
Summary:
- Force HANDLER_EXIT even for SIGNAL_UNKILLABLE
- Make seccomp self-destruct after fatal filter results
- Update seccomp samples for easier behavioral demonstration"
* tag 'seccomp-v5.17-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
samples/seccomp: Adjust sample to also provide kill option
seccomp: Invalidate seccomp mode to catch death failures
signal: HANDLER_EXIT should clear SIGNAL_UNKILLABLE
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 4d8f44a..db10e73 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -29,6 +29,9 @@
#include <linux/syscalls.h>
#include <linux/sysctl.h>
+/* Not exposed in headers: strictly internal use only. */
+#define SECCOMP_MODE_DEAD (SECCOMP_MODE_FILTER + 1)
+
#ifdef CONFIG_HAVE_ARCH_SECCOMP_FILTER
#include <asm/syscall.h>
#endif
@@ -1010,6 +1013,7 @@ static void __secure_computing_strict(int this_syscall)
#ifdef SECCOMP_DEBUG
dump_stack();
#endif
+ current->seccomp.mode = SECCOMP_MODE_DEAD;
seccomp_log(this_syscall, SIGKILL, SECCOMP_RET_KILL_THREAD, true);
do_exit(SIGKILL);
}
@@ -1261,6 +1265,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
case SECCOMP_RET_KILL_THREAD:
case SECCOMP_RET_KILL_PROCESS:
default:
+ current->seccomp.mode = SECCOMP_MODE_DEAD;
seccomp_log(this_syscall, SIGSYS, action, true);
/* Dump core only if this is the last remaining thread. */
if (action != SECCOMP_RET_KILL_THREAD ||
@@ -1309,6 +1314,11 @@ int __secure_computing(const struct seccomp_data *sd)
return 0;
case SECCOMP_MODE_FILTER:
return __seccomp_filter(this_syscall, sd, false);
+ /* Surviving SECCOMP_RET_KILL_* must be proactively impossible. */
+ case SECCOMP_MODE_DEAD:
+ WARN_ON_ONCE(1);
+ do_exit(SIGKILL);
+ return -1;
default:
BUG();
}
diff --git a/kernel/signal.c b/kernel/signal.c
index 3860273..9b04631 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1342,9 +1342,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
}
/*
* Don't clear SIGNAL_UNKILLABLE for traced tasks, users won't expect
- * debugging to leave init killable.
+ * debugging to leave init killable. But HANDLER_EXIT is always fatal.
*/
- if (action->sa.sa_handler == SIG_DFL && !t->ptrace)
+ if (action->sa.sa_handler == SIG_DFL &&
+ (!t->ptrace || (handler == HANDLER_EXIT)))
t->signal->flags &= ~SIGNAL_UNKILLABLE;
ret = send_signal(sig, info, t, PIDTYPE_PID);
spin_unlock_irqrestore(&t->sighand->siglock, flags);
diff --git a/samples/seccomp/dropper.c b/samples/seccomp/dropper.c
index cc0648e..4bca4b7 100644
--- a/samples/seccomp/dropper.c
+++ b/samples/seccomp/dropper.c
@@ -25,7 +25,7 @@
#include <sys/prctl.h>
#include <unistd.h>
-static int install_filter(int nr, int arch, int error)
+static int install_filter(int arch, int nr, int error)
{
struct sock_filter filter[] = {
BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
@@ -42,6 +42,10 @@ static int install_filter(int nr, int arch, int error)
.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
.filter = filter,
};
+ if (error == -1) {
+ struct sock_filter kill = BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL);
+ filter[4] = kill;
+ }
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
perror("prctl(NO_NEW_PRIVS)");
return 1;
@@ -57,9 +61,10 @@ int main(int argc, char **argv)
{
if (argc < 5) {
fprintf(stderr, "Usage:\n"
- "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
+ "dropper <arch> <syscall_nr> <errno> <prog> [<args>]\n"
"Hint: AUDIT_ARCH_I386: 0x%X\n"
" AUDIT_ARCH_X86_64: 0x%X\n"
+ " errno == -1 means SECCOMP_RET_KILL\n"
"\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
return 1;
}