BACKPORT: 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.

v18: - rebase
     - comment fatal_signal check
     - acked-by
v17: - ...
v16: - update PT_TRACE_MASK to 0xbf4 so that STOP isn't clear on SETOPTIONS call (indan@nul.nu)
       [note PT_TRACE_MASK disappears in linux-next]
v15: - add audit support for non-zero return codes
     - clean up style (indan@nul.nu)
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@redhat.com)
v11: - invert the logic to just make it a PTRACE_SYSCALL accelerator
       (indan@nul.nu)
v10: - moved to PTRACE_O_SECCOMP / PT_TRACE_SECCOMP
v9:  - n/a
v8:  - guarded PTRACE_SECCOMP use with an ifdef
v7:  - introduced

Change-Id: I1a6b98cc3dad0be83f856279f850f718a9888b53
Acked-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Will Drewry <wad@chromium.org>
BUG=chromium-os:27878
TEST=none. Part of a much larger stack that really should merge together.

Change-Id: I1ba0786303612deae64878f8a8396541a9553a89
Reviewed-on: https://gerrit.chromium.org/gerrit/21368
Reviewed-by: Will Drewry <wad@chromium.org>
Tested-by: Will Drewry <wad@chromium.org>

diff --git a/arch/Kconfig b/arch/Kconfig
index d5f3869..ed5702d 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -219,15 +219,16 @@ config ARCH_WANT_OLD_COMPAT_IPC
 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..26bf736 100644 (file)
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -51,6 +51,9 @@
 #define PTRACE_INTERRUPT       0x4207
 #define PTRACE_LISTEN          0x4208
 
+/* flags in @data for PTRACE_SEIZE */
+#define PTRACE_SEIZE_DEVEL     0x80000000 /* temp flag for development */
+
 /* Wait extended result codes for the above trace options.  */
 #define PTRACE_EVENT_FORK      1
 #define PTRACE_EVENT_VFORK     2
@@ -58,6 +61,8 @@
 #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
 
@@ -69,6 +74,7 @@
 #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
 
@@ -98,6 +104,9 @@
 #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)
+
+#define PT_TRACE_MASK  0x000007f4
 
 /* 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 (file)
--- 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/ptrace.c b/kernel/ptrace.c
index ee8d49b..a51f76b 100644 (file)
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -535,6 +535,9 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
        flags |= (data << PT_OPT_FLAG_SHIFT);
        child->ptrace = flags;
 
+       if (data & PTRACE_O_TRACESECCOMP)
+               child->ptrace |= PT_TRACE_SECCOMP;
+
        return 0;
 }
 

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index b1ec240..aa2faab 100644 (file)
--- 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>
@@ -403,7 +404,7 @@ 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),
@@ -415,6 +416,21 @@ 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);
+                       /*
+                        * The delivery of a fatal signal during event
+                        * notification may silently skip tracer notification.
+                        * Terminating the task now avoids executing a system
+                        * call that may not be intended.
+                        */
+                       if (fatal_signal_pending(current))
+                               break;
+                       return 0;
                case SECCOMP_RET_ALLOW:
                        return 0;
                case SECCOMP_RET_KILL: