ptrace, seccomp: add support for retrieving seccomp metadata

With the new SECCOMP_FILTER_FLAG_LOG, we need to be able to extract these
flags for checkpoint restore, since they describe the state of a filter.

So, let's add PTRACE_SECCOMP_GET_METADATA, similar to ..._GET_FILTER, which
returns the metadata of the nth filter (right now, just the flags).
Hopefully this will be future proof, and new per-filter metadata can be
added to this struct.

Signed-off-by: Tycho Andersen <tycho@docker.com>
CC: Kees Cook <keescook@chromium.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

4 files changed, 51 insertions, 0 deletions

diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index 10f25f7e4304..c723a5c4e3ff 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -95,11 +95,19 @@ static inline void get_seccomp_filter(struct task_struct *tsk)
 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
 extern long seccomp_get_filter(struct task_struct *task,
                                unsigned long filter_off, void __user *data);
+extern long seccomp_get_metadata(struct task_struct *task,
+                                 unsigned long filter_off, void __user *data);
 #else
 static inline long seccomp_get_filter(struct task_struct *task,
                                       unsigned long n, void __user *data)
 {
         return -EINVAL;
 }
+static inline long seccomp_get_metadata(struct task_struct *task,
+                                        unsigned long filter_off,
+                                        void __user *data)
+{
+        return -EINVAL;
+}
 #endif /* CONFIG_SECCOMP_FILTER && CONFIG_CHECKPOINT_RESTORE */
 #endif /* _LINUX_SECCOMP_H */
diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
index e3939e00980b..e46d82b91166 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -66,6 +66,12 @@ struct ptrace_peeksiginfo_args {
 #define PTRACE_SETSIGMASK       0x420b
 
 #define PTRACE_SECCOMP_GET_FILTER       0x420c
+#define PTRACE_SECCOMP_GET_METADATA     0x420d
+
+struct seccomp_metadata {
+        unsigned long filter_off;       /* Input: which filter */
+        unsigned int flags;             /* Output: filter's flags */
+};
 
 /* Read signals from a shared (process wide) queue */
 #define PTRACE_PEEKSIGINFO_SHARED       (1 << 0)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 84b1367935e4..58291e9f3276 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1092,6 +1092,10 @@ int ptrace_request(struct task_struct *child, long request,
                 ret = seccomp_get_filter(child, addr, datavp);
                 break;
 
+        case PTRACE_SECCOMP_GET_METADATA:
+                ret = seccomp_get_metadata(child, addr, datavp);
+                break;
+
         default:
                 break;
         }
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 99bddaf79076..61bd9dc260c8 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -1061,6 +1061,39 @@ out:
         __put_seccomp_filter(filter);
         return ret;
 }
+
+long seccomp_get_metadata(struct task_struct *task,
+                          unsigned long size, void __user *data)
+{
+        long ret;
+        struct seccomp_filter *filter;
+        struct seccomp_metadata kmd = {};
+
+        if (!capable(CAP_SYS_ADMIN) ||
+            current->seccomp.mode != SECCOMP_MODE_DISABLED) {
+                return -EACCES;
+        }
+
+        size = min_t(unsigned long, size, sizeof(kmd));
+
+        if (copy_from_user(&kmd, data, size))
+                return -EFAULT;
+
+        filter = get_nth_filter(task, kmd.filter_off);
+        if (IS_ERR(filter))
+                return PTR_ERR(filter);
+
+        memset(&kmd, 0, sizeof(kmd));
+        if (filter->log)
+                kmd.flags |= SECCOMP_FILTER_FLAG_LOG;
+
+        ret = size;
+        if (copy_to_user(data, &kmd, size))
+                ret = -EFAULT;
+
+        __put_seccomp_filter(filter);
+        return ret;
+}
 #endif
 
 #ifdef CONFIG_SYSCTL