ptrace,seccomp: Add PTRACE_SECCOMP support

This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP, and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE. When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that results in a BPF program returning SECCOMP_RET_TRACE. The 16-bit SECCOMP_RET_DATA mask of the BPF program return value will be passed as the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG. If the subordinate process is not using seccomp filter, then no system call notifications will occur even if the option is specified. If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE is returned, the system call will not be executed and an -ENOSYS errno will be returned to userspace. This change adds a dependency on the system call slow path. Any future efforts to use the system call fast path for seccomp filter will need to address this restriction. Signed-off-by: Will Drewry <wad@chromium.org> Acked-by: Eric Paris <eparis@redhat.com>

Will Drewry committed 14 years ago

Commit fb0fadf1 parent bb6ea434 files · +26 −6Browse files

Unified · Split

4 files

arch/Kconfig +5 −5
include/linux/ptrace.h +4 −1
include/linux/seccomp.h +1 −0
kernel/seccomp.c +16 −0

arch/Kconfig+5−5

@@ -219,15 +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:
	222	+ An arch should select this symbol if it provides all of these things:
224	223	- syscall_get_arch()
225	224	- syscall_get_arguments()
226	225	- syscall_rollback()
227	226	- 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	+ - SIGSYS siginfo_t support
	228	+ - secure_computing is called from a ptrace_event()-safe context
	229	+ - secure_computing return value is checked and a return value of -1
	230	+ results in the system call being skipped immediately.
231	231
232	232	config SECCOMP_FILTER
233	233	def_bool y

include/linux/ptrace.h+4−1

@@ -58,6 +58,7 @@ · 57 unmodified lines
58	58	#define PTRACE_EVENT_EXEC 4
59	59	#define PTRACE_EVENT_VFORK_DONE 5
60	60	#define PTRACE_EVENT_EXIT 6
	61	+#define PTRACE_EVENT_SECCOMP 7
61	62	/* Extended result codes which enabled by means other than options. */
62	63	#define PTRACE_EVENT_STOP 128
63	64
@@ -69,8 +70,9 @@ · 5 unmodified lines
69	70	#define PTRACE_O_TRACEEXEC (1 << PTRACE_EVENT_EXEC)
70	71	#define PTRACE_O_TRACEVFORKDONE (1 << PTRACE_EVENT_VFORK_DONE)
71	72	#define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT)
	73	+#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP)
72	74
73		−#define PTRACE_O_MASK 0x0000007f
	75	+#define PTRACE_O_MASK 0x000000ff
74	76
75	77	#include <asm/ptrace.h>
76	78
@@ -98,6 +100,7 @@ · 21 unmodified lines
98	100	#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
99	101	#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
100	102	#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
	103	+#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)
101	104
102	105	/* single stepping state bits (used on ARM and PA-RISC) */
103	106	#define PT_SINGLESTEP_BIT 31

include/linux/seccomp.h+1−0

@@ -21,6 +21,7 @@ · 20 unmodified lines
21	21	#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
22	22	#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
23	23	#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
	24	+#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
24	25	#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
25	26
26	27	/* Masks for the return value sections. */

kernel/seccomp.c+16−0

@@ -24,6 +24,7 @@ · 23 unmodified lines
24	24	#ifdef CONFIG_SECCOMP_FILTER
25	25	#include <asm/syscall.h>
26	26	#include <linux/filter.h>
	27	+#include <linux/ptrace.h>
27	28	#include <linux/security.h>
28	29	#include <linux/slab.h>
29	30	#include <linux/tracehook.h>
@@ -408,6 +409,21 @@ int __secure_computing(int this_syscall) · 378 unmodified lines
408	409	/* Let the filter pass back 16 bits of data. */
409	410	seccomp_send_sigsys(this_syscall, data);
410	411	goto skip;
	412	+ case SECCOMP_RET_TRACE:
	413	+ /* Skip these calls if there is no tracer. */
	414	+ if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP))
	415	+ goto skip;
	416	+ /* Allow the BPF to provide the event message */
	417	+ ptrace_event(PTRACE_EVENT_SECCOMP, data);
	418	+ /*
	419	+ * The delivery of a fatal signal during event
	420	+ * notification may silently skip tracer notification.
	421	+ * Terminating the task now avoids executing a system
	422	+ * call that may not be intended.
	423	+ */
	424	+ if (fatal_signal_pending(current))
	425	+ break;
	426	+ return 0;
411	427	case SECCOMP_RET_ALLOW:
412	428	return 0;
413	429	case SECCOMP_RET_KILL: