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seccomp fixes for v5.17-rc4

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- Force HANDLER_EXIT even for SIGNAL_UNKILLABLE.
 - Make seccomp self-destruct after fatal filter results.
 - Update seccomp samples for easier behavioral demonstration.
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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
This commit is contained in:
Linus Torvalds 2022-02-12 09:04:05 -08:00
commit eef8cffcab
3 changed files with 20 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
kernel/seccomp.c
View File

@ -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();
}

5
kernel/signal.c
View File

@ -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);

9
samples/seccomp/dropper.c
View File

@ -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;
}