seccomp: Add SECCOMP_RET_TRAP

Adds a new return value to seccomp filters that triggers a SIGSYS to be delivered with the new SYS_SECCOMP si_code. This allows in-process system call emulation, including just specifying an errno or cleanly dumping core, rather than just dying. Suggested-by: Markus Gutschke <markus@chromium.org> Suggested-by: Julien Tinnes <jln@chromium.org> Signed-off-by: Will Drewry <wad@chromium.org> Acked-by: Eric Paris <eparis@redhat.com>

Will Drewry committed 14 years ago

Commit bb6ea431 parent a0727e84 files · +37 −6Browse files

Unified · Split

4 files

arch/Kconfig +9 −5
include/asm-generic/siginfo.h +1 −1
include/linux/seccomp.h +1 −0
kernel/seccomp.c +26 −0

arch/Kconfig+9−5

@@ -219,11 +219,15 @@ config ARCH_WANT_OLD_COMPAT_IPC · 218 unmodified lines
219	219	config HAVE_ARCH_SECCOMP_FILTER
220	220	bool
221	221	help
222		− This symbol should be selected by an architecure if it provides
223		− asm/syscall.h, specifically syscall_get_arguments(),
224		− syscall_get_arch(), and syscall_set_return_value(). Additionally,
225		− its system call entry path must respect a return value of -1 from
226		− __secure_computing() and/or secure_computing().
	222	+ This symbol should be selected by an architecure if it provides:
	223	+ asm/syscall.h:
	224	+ - syscall_get_arch()
	225	+ - syscall_get_arguments()
	226	+ - syscall_rollback()
	227	+ - syscall_set_return_value()
	228	+ SIGSYS siginfo_t support must be implemented.
	229	+ __secure_computing()/secure_computing()'s return value must be
	230	+ checked, with -1 resulting in the syscall being skipped.
227	231
228	232	config SECCOMP_FILTER
229	233	def_bool y

include/asm-generic/siginfo.h+1−1

@@ -93,7 +93,7 @@ typedef struct siginfo { · 92 unmodified lines
93	93
94	94	/* SIGSYS */
95	95	struct {
96		− void __user _call_addr; / calling insn */
	96	+ void __user _call_addr; / calling user insn */
97	97	int _syscall; /* triggering system call number */
98	98	unsigned int _arch; /* AUDIT_ARCH_* of syscall */
99	99	} _sigsys;

include/linux/seccomp.h+1−0

@@ -19,6 +19,7 @@ · 18 unmodified lines
19	19	* selects the least permissive choice.
20	20	*/
21	21	#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
	22	+#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
22	23	#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
23	24	#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
24	25

kernel/seccomp.c+26−0

@@ -332,6 +332,26 @@ void put_seccomp_filter(struct task_struct *tsk) · 331 unmodified lines
332	332	kfree(freeme);
333	333	}
334	334	}
	335	+
	336	+/**
	337	+ * seccomp_send_sigsys - signals the task to allow in-process syscall emulation
	338	+ * @syscall: syscall number to send to userland
	339	+ * @reason: filter-supplied reason code to send to userland (via si_errno)
	340	+ *
	341	+ * Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
	342	+ */
	343	+static void seccomp_send_sigsys(int syscall, int reason)
	344	+{
	345	+ struct siginfo info;
	346	+ memset(&info, 0, sizeof(info));
	347	+ info.si_signo = SIGSYS;
	348	+ info.si_code = SYS_SECCOMP;
	349	+ info.si_call_addr = (void __user *)KSTK_EIP(current);
	350	+ info.si_errno = reason;
	351	+ info.si_arch = syscall_get_arch(current, task_pt_regs(current));
	352	+ info.si_syscall = syscall;
	353	+ force_sig_info(SIGSYS, &info, current);
	354	+}
335	355	#endif /* CONFIG_SECCOMP_FILTER */
336	356
337	357	/*
@@ -382,6 +402,12 @@ int __secure_computing(int this_syscall) · 44 unmodified lines
382	402	syscall_set_return_value(current, task_pt_regs(current),
383	403	-data, 0);
384	404	goto skip;
	405	+ case SECCOMP_RET_TRAP:
	406	+ /* Show the handler the original registers. */
	407	+ syscall_rollback(current, task_pt_regs(current));
	408	+ /* Let the filter pass back 16 bits of data. */
	409	+ seccomp_send_sigsys(this_syscall, data);
	410	+ goto skip;
385	411	case SECCOMP_RET_ALLOW:
386	412	return 0;
387	413	case SECCOMP_RET_KILL: