[PATCH] ptrace, seccomp: add support for retrieving seccomp flags

[Tycho Andersen]

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_FLAGS, similar to ..._GET_FILTER, which
returns the flags of the nth filter.

Signed-off-by: Tycho Andersen <tycho@xxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 include/linux/seccomp.h     |  7 +++++
 include/uapi/linux/ptrace.h |  1 +
 kernel/ptrace.c             |  4 +++
 kernel/seccomp.c            | 74 ++++++++++++++++++++++++++++++++++-----------
 4 files changed, 68 insertions(+), 18 deletions(-)

diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index c8bef436b61d..4713d62378e3 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -94,11 +94,18 @@ 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_flags(struct task_struct *task,
+			      unsigned long filter_off);
 #else
 static inline long seccomp_get_filter(struct task_struct *task,
 				      unsigned long n, void __user *data)
 {
 	return -EINVAL;
 }
+static inline long seccomp_get_flags(struct task_struct *task,
+				     unsigned long filter_off)
+{
+	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 fb8106509000..52903f0f6600 100644
--- a/include/uapi/linux/ptrace.h
+++ b/include/uapi/linux/ptrace.h
@@ -65,6 +65,7 @@ struct ptrace_peeksiginfo_args {
 #define PTRACE_SETSIGMASK	0x420b
 
 #define PTRACE_SECCOMP_GET_FILTER	0x420c
+#define PTRACE_SECCOMP_GET_FLAGS	0x420d
 
 /* 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 60f356d91060..fa3d2b4d3bf0 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1094,6 +1094,10 @@ int ptrace_request(struct task_struct *child, long request,
 		ret = seccomp_get_filter(child, addr, datavp);
 		break;
 
+	case PTRACE_SECCOMP_GET_FLAGS:
+		ret = seccomp_get_flags(child, addr);
+		break;
+
 	default:
 		break;
 	}
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index c24579dfa7a1..67768aaa7952 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -968,24 +968,16 @@ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 }
 
 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
-long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
-			void __user *data)
+static struct seccomp_filter *get_nth_filter(struct task_struct *task,
+					     unsigned long filter_off)
 {
 	struct seccomp_filter *filter;
-	struct sock_fprog_kern *fprog;
-	long ret;
 	unsigned long count = 0;
 
-	if (!capable(CAP_SYS_ADMIN) ||
-	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
-		return -EACCES;
-	}
+	WARN_ON_ONCE(!spin_is_locked(&task->sighand->siglock));
 
-	spin_lock_irq(&task->sighand->siglock);
-	if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (task->seccomp.mode != SECCOMP_MODE_FILTER)
+		return ERR_PTR(-EINVAL);
 
 	filter = task->seccomp.filter;
 	while (filter) {
@@ -993,10 +985,9 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 		count++;
 	}
 
-	if (filter_off >= count) {
-		ret = -ENOENT;
-		goto out;
-	}
+	if (filter_off >= count)
+		return ERR_PTR(-ENOENT);
+
 	count -= filter_off;
 
 	filter = task->seccomp.filter;
@@ -1007,7 +998,28 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 
 	if (WARN_ON(count != 1 || !filter)) {
 		/* The filter tree shouldn't shrink while we're using it. */
-		ret = -ENOENT;
+		return ERR_PTR(-ENOENT);
+	}
+
+	return filter;
+}
+
+long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
+			void __user *data)
+{
+	struct seccomp_filter *filter;
+	struct sock_fprog_kern *fprog;
+	long ret;
+
+	if (!capable(CAP_SYS_ADMIN) ||
+	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
+		return -EACCES;
+	}
+
+	spin_lock_irq(&task->sighand->siglock);
+	filter = get_nth_filter(task, filter_off);
+	if (IS_ERR(filter)) {
+		ret = PTR_ERR(filter);
 		goto out;
 	}
 
@@ -1038,6 +1050,32 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 	spin_unlock_irq(&task->sighand->siglock);
 	return ret;
 }
+
+long seccomp_get_flags(struct task_struct *task, unsigned long filter_off)
+{
+	long flags = 0L;
+	struct seccomp_filter *filter;
+
+	if (!capable(CAP_SYS_ADMIN) ||
+	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
+		return -EACCES;
+	}
+
+	spin_lock_irq(&task->sighand->siglock);
+	filter = get_nth_filter(task, filter_off);
+	if (IS_ERR(filter)) {
+		flags = PTR_ERR(filter);
+		goto out;
+	}
+
+	if (filter->log)
+		flags |= SECCOMP_FILTER_FLAG_LOG;
+
+out:
+	spin_unlock_irq(&task->sighand->siglock);
+	return flags;
+
+}
 #endif
 
 #ifdef CONFIG_SYSCTL
-- 
2.11.0