seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()

From: Oleg Nesterov <[email protected]>

As Chris explains, get_seccomp_filter() and put_seccomp_filter() can use the different filters, once we drop ->siglock task->seccomp.filter can be replaced by SECCOMP_FILTER_FLAG_TSYNC.

v2: add __get_seccomp_filter vs. open coding refcount_inc()

Fixes f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters")

Reported-by Chris Salls <[email protected]>

Cc [email protected]

Signed-off-by Oleg Nesterov <[email protected]>

Signed-off-by Tycho Andersen <[email protected]>

---
 kernel/seccomp.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

kernel/seccomp.c +16 -8

index c24579dfa7a1..bb3a38005b9c 100644
@@ -473,14 +473,19 @@ static long seccomp_attach_filter(unsigned int flags,
        return 0;
 }
 
+void __get_seccomp_filter(struct seccomp_filter *filter)
+{
+       /* Reference count is bounded by the number of total processes. */
+       refcount_inc(&filter->usage);
+}
+
 /* get_seccomp_filter - increments the reference count of the filter on @tsk */
 void get_seccomp_filter(struct task_struct *tsk)
 {
        struct seccomp_filter *orig = tsk->seccomp.filter;
        if (!orig)
                return;
-       /* Reference count is bounded by the number of total processes. */
-       refcount_inc(&orig->usage);
+       __get_seccomp_filter(orig);
 }
 
 static inline void seccomp_filter_free(struct seccomp_filter *filter)

@@ -491,10 +496,8 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter)
        }
 }
 
-/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
-void put_seccomp_filter(struct task_struct *tsk)
+static void __put_seccomp_filter(struct seccomp_filter *orig)
 {
-       struct seccomp_filter *orig = tsk->seccomp.filter;
        /* Clean up single-reference branches iteratively. */
        while (orig && refcount_dec_and_test(&orig->usage)) {
                struct seccomp_filter *freeme = orig;

@@ -503,6 +506,12 @@ void put_seccomp_filter(struct task_struct *tsk)
        }
 }
 
+/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
+void put_seccomp_filter(struct task_struct *tsk)
+{
+       __put_seccomp_filter(tsk->seccomp.filter);
+}
+
 static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
 {
        memset(info, 0, sizeof(*info));

@@ -1025,13 +1034,13 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
        if (!data)
                goto out;
 
-       get_seccomp_filter(task);
+       __get_seccomp_filter(filter);
        spin_unlock_irq(&task->sighand->siglock);
 
        if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
                ret = -EFAULT;
 
-       put_seccomp_filter(task);
+       __put_seccomp_filter(filter);
        return ret;
 
 out:
--

2.11.0