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signal/seccomp: Refactor seccomp signal and coredump generation 

Factor out force_sig_seccomp from the seccomp signal generation and
place it in kernel/signal.c.  The function force_sig_seccomp takes a
parameter 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.

Further it no longer becomes necessary for __seccomp_filter
to call do_group_exit.

Acked-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87r1gr6qc4.fsf_-_@disp2133
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2021-06-23 16:44:32 -05:00
parent a3616a3c02
commit 307d522f5e
3 changed files with 33 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/sched/signal.h
View File

@ -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);

40
kernel/seccomp.c
View File

@ -922,30 +922,6 @@ 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 */
@ -1218,7 +1194,7 @@ 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:
@ -1289,18 +1265,14 @@ 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);
}
if (action == SECCOMP_RET_KILL_THREAD)
/* Trigger a coredump with SIGSYS */
force_sig_seccomp(this_syscall, data, true);
} else {
do_exit(SIGSYS);
else
do_group_exit(SIGSYS);
}
return -1; /* skip the syscall go directly to signal handling */
}
unreachable();

30
kernel/signal.c
View File

@ -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.
@ -1322,7 +1323,7 @@ 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;
@ -1333,7 +1334,7 @@ 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);
@ -1354,7 +1355,7 @@ 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);
}
/*
@ -1685,7 +1686,7 @@ 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
@ -1793,6 +1794,27 @@ 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.
*/