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Subject[PATCH] ptrace, seccomp: add support for retrieving seccomp flags
Date
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@docker.com>
CC: Kees Cook <keescook@chromium.org>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
---
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
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