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.
v17: - rebase onto refactored ptrace code now in -linus
v16: - update PT_TRACE_MASK to 0xbf4 so that STOP isn't clear on SETOPTIONS call (indan@xxxxxx)
[note PT_TRACE_MASK disappears in linux-next]
v15: - add audit support for non-zero return codes
- clean up style (indan@xxxxxx)
v14: - rebase/nochanges
v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
(Brings back a change to ptrace.c and the masks.)
v12: - rebase to linux-next
- use ptrace_event and update arch/Kconfig to mention slow-path dependency
- drop all tracehook changes and inclusion (oleg@xxxxxxxxxx)
v11: - invert the logic to just make it a PTRACE_SYSCALL accelerator
(indan@xxxxxx)
v10: - moved to PTRACE_O_SECCOMP / PT_TRACE_SECCOMP
v9: - n/a
v8: - guarded PTRACE_SECCOMP use with an ifdef
v7: - introduced
Signed-off-by: Will Drewry <wad@xxxxxxxxxxxx>
---
arch/Kconfig | 11 ++++++-----
include/linux/ptrace.h | 5 ++++-
include/linux/seccomp.h | 1 +
kernel/seccomp.c | 12 +++++++++++-
4 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index a24d213..fafefe6 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -216,15 +216,16 @@ config HAVE_CMPXCHG_DOUBLE
config HAVE_ARCH_SECCOMP_FILTER
bool
help
- This symbol should be selected by an architecure if it provides:
- asm/syscall.h:
+ An arch should select this symbol if it provides all of these things:
- syscall_get_arch()
- syscall_get_arguments()
- syscall_rollback()
- syscall_set_return_value()
- SIGSYS siginfo_t support must be implemented.
- __secure_computing_int()/secure_computing()'s return value must be
- checked, with -1 resulting in the syscall being skipped.
+ - SIGSYS siginfo_t support
+ - uses __secure_computing_int() or secure_computing()
+ - secure_computing is called from a ptrace_event()-safe context
+ - secure_computing return value is checked and a return value of -1
+ results in the system call being skipped immediately.
config SECCOMP_FILTER
def_bool y
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 5c71962..597e4fd 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -58,6 +58,7 @@
#define PTRACE_EVENT_EXEC 4
#define PTRACE_EVENT_VFORK_DONE 5
#define PTRACE_EVENT_EXIT 6
+#define PTRACE_EVENT_SECCOMP 7
/* Extended result codes which enabled by means other than options. */
#define PTRACE_EVENT_STOP 128
@@ -69,8 +70,9 @@
#define PTRACE_O_TRACEEXEC (1 << PTRACE_EVENT_EXEC)
#define PTRACE_O_TRACEVFORKDONE (1 << PTRACE_EVENT_VFORK_DONE)
#define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT)
+#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP)
-#define PTRACE_O_MASK 0x0000007f
+#define PTRACE_O_MASK 0x000000ff
#include <asm/ptrace.h>
@@ -98,6 +100,7 @@
#define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC)
#define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE)
#define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT)
+#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP)
/* single stepping state bits (used on ARM and PA-RISC) */
#define PT_SINGLESTEP_BIT 31
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index ecec06c..41ff13b 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -21,6 +21,7 @@
#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
+#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
/* Masks for the return value sections. */
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 9a59c93..4b5affa 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -24,6 +24,7 @@
#ifdef CONFIG_SECCOMP_FILTER
#include <asm/syscall.h>
#include <linux/filter.h>
+#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/slab.h>
#include <linux/tracehook.h>
@@ -398,7 +399,7 @@ int __secure_computing_int(int this_syscall)
case SECCOMP_MODE_FILTER:
ret = seccomp_run_filters(this_syscall);
data = ret & SECCOMP_RET_DATA;
- switch (code & SECCOMP_RET_ACTION) {
+ switch (ret & SECCOMP_RET_ACTION) {
case SECCOMP_RET_ERRNO:
/* Set the low-order 16-bits as a errno. */
syscall_set_return_value(current, task_pt_regs(current),
@@ -410,6 +411,15 @@ int __secure_computing_int(int this_syscall)
/* Let the filter pass back 16 bits of data. */
seccomp_send_sigsys(this_syscall, data);
goto skip;
+ case SECCOMP_RET_TRACE:
+ /* Skip these calls if there is no tracer. */
+ if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP))
+ goto skip;
+ /* Allow the BPF to provide the event message */
+ ptrace_event(PTRACE_EVENT_SECCOMP, data);
+ if (fatal_signal_pending(current))
+ break;
+ return 0;
case SECCOMP_RET_ALLOW:
return 0;
case SECCOMP_RET_KILL:
--
1.7.5.4
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