[PATCH 2/9] signal/seccomp: Refactor seccomp signal and coredump generation

Eric W. Biederman
2021-06-24T19:00:10Z

Factor out force_sig_seccomp from the seccomp signal generation and
place it in kernel/signal.c. The function force_sig_seccomp takes a
paramter force_coredump to indicate that the sigaction field should be
reset to SIGDFL so that a coredump will be generated when the signal
is delivered.

force_sig_seccomp is then used to replace both seccomp_send_sigsys
and seccomp_init_siginfo.

force_sig_info_to_task gains an extra parameter to force using
the default signal action.

With this change seccomp is no longer a special case and there
becomes exactly one place do_coredump is called from.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
include/linux/sched/signal.h | 1 +
kernel/seccomp.c | 43 ++++++++----------------------------
kernel/signal.c | 30 +++++++++++++++++++++----
3 files changed, 36 insertions(+), 38 deletions(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 7f4278fa21fe..774be5d3ac3e 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -329,6 +329,7 @@ int force_sig_pkuerr(void __user *addr, u32 pkey);
int force_sig_perf(void __user *addr, u32 type, u64 sig_data);

int force_sig_ptrace_errno_trap(int errno, void __user *addr);
+int force_sig_seccomp(int syscall, int reason, bool force_coredump);

extern int send_sig_info(int, struct kernel_siginfo *, struct task_struct *);
extern void force_sigsegv(int sig);
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 6ecd3f3a52b5..3e06d4628d98 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -920,30 +920,6 @@ void get_seccomp_filter(struct task_struct *tsk)
refcount_inc(&orig->users);
}

-static void seccomp_init_siginfo(kernel_siginfo_t *info, int syscall, int reason)
-{
- clear_siginfo(info);
- info->si_signo = SIGSYS;
- info->si_code = SYS_SECCOMP;
- info->si_call_addr = (void __user *)KSTK_EIP(current);
- info->si_errno = reason;
- info->si_arch = syscall_get_arch(current);
- info->si_syscall = syscall;
-}
-
-/**
- * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
- * @syscall: syscall number to send to userland
- * @reason: filter-supplied reason code to send to userland (via si_errno)
- *
- * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
- */
-static void seccomp_send_sigsys(int syscall, int reason)
-{
- struct kernel_siginfo info;
- seccomp_init_siginfo(&info, syscall, reason);
- force_sig_info(&info);
-}
#endif /* CONFIG_SECCOMP_FILTER */

/* For use with seccomp_actions_logged */
@@ -1195,7 +1171,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
/* Show the handler the original registers. */
syscall_rollback(current, current_pt_regs());
/* Let the filter pass back 16 bits of data. */
- seccomp_send_sigsys(this_syscall, data);
+ force_sig_seccomp(this_syscall, data, false);
goto skip;

case SECCOMP_RET_TRACE:
@@ -1266,18 +1242,17 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
/* Dump core only if this is the last remaining thread. */
if (action != SECCOMP_RET_KILL_THREAD ||
get_nr_threads(current) == 1) {
- kernel_siginfo_t info;
-
/* Show the original registers in the dump. */
syscall_rollback(current, current_pt_regs());
- /* Trigger a manual coredump since do_exit skips it. */
- seccomp_init_siginfo(&info, this_syscall, data);
- do_coredump(&info);
+ /* Trigger a coredump with SIGSYS */
+ force_sig_seccomp(this_syscall, data, true);
+ } else {
+ if (action == SECCOMP_RET_KILL_THREAD)
+ do_exit(SIGSYS);
+ else
+ do_group_exit(SIGSYS);
}
- if (action == SECCOMP_RET_KILL_THREAD)
- do_exit(SIGSYS);
- else
- do_group_exit(SIGSYS);
+ return -1;
}

unreachable();
diff --git a/kernel/signal.c b/kernel/signal.c
index f7c6ffcbd044..da37cc4515f2 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -54,6 +54,7 @@
#include <asm/unistd.h>
#include <asm/siginfo.h>
#include <asm/cacheflush.h>
+#include <asm/syscall.h> /* for syscall_get_* */

/*
* SLAB caches for signal bits.
@@ -1349,7 +1350,7 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
* that is why we also clear SIGNAL_UNKILLABLE.
*/
static int
-force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t)
+force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool sigdfl)
{
unsigned long int flags;
int ret, blocked, ignored;
@@ -1360,7 +1361,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t)
action = &t->sighand->action[sig-1];
ignored = action->sa.sa_handler == SIG_IGN;
blocked = sigismember(&t->blocked, sig);
- if (blocked || ignored) {
+ if (blocked || ignored || sigdfl) {
action->sa.sa_handler = SIG_DFL;
if (blocked) {
sigdelset(&t->blocked, sig);
@@ -1381,7 +1382,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t)

int force_sig_info(struct kernel_siginfo *info)
{
- return force_sig_info_to_task(info, current);
+ return force_sig_info_to_task(info, current, false);
}

/*
@@ -1712,7 +1713,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr
info.si_flags = flags;
info.si_isr = isr;
#endif
- return force_sig_info_to_task(&info, t);
+ return force_sig_info_to_task(&info, t, false);
}

int force_sig_fault(int sig, int code, void __user *addr
@@ -1820,6 +1821,27 @@ int force_sig_perf(void __user *addr, u32 type, u64 sig_data)
return force_sig_info(&info);
}

+/**
+ * force_sig_seccomp - signals the task to allow in-process syscall emulation
+ * @syscall: syscall number to send to userland
+ * @reason: filter-supplied reason code to send to userland (via si_errno)
+ *
+ * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
+ */
+int force_sig_seccomp(int syscall, int reason, bool force_coredump)
+{
+ struct kernel_siginfo info;
+
+ clear_siginfo(&info);
+ info.si_signo = SIGSYS;
+ info.si_code = SYS_SECCOMP;
+ info.si_call_addr = (void __user *)KSTK_EIP(current);
+ info.si_errno = reason;
+ info.si_arch = syscall_get_arch(current);
+ info.si_syscall = syscall;
+ return force_sig_info_to_task(&info, current, force_coredump);
+}
+
/* For the crazy architectures that include trap information in
* the errno field, instead of an actual errno value.
*/
--
2.20.1