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Subject[PATCH 4.13 075/110] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()
Date
4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Oleg Nesterov <oleg@redhat.com>

commit 66a733ea6b611aecf0119514d2dddab5f9d6c01e upstream.

As Chris explains, get_seccomp_filter() and put_seccomp_filter() can end
up using different filters. Once we drop ->siglock it is possible for
task->seccomp.filter to have been replaced by SECCOMP_FILTER_FLAG_TSYNC.

Fixes: f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters")
Reported-by: Chris Salls <chrissalls5@gmail.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
[tycho: add __get_seccomp_filter vs. open coding refcount_inc()]
Signed-off-by: Tycho Andersen <tycho@docker.com>
[kees: tweak commit log]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -458,14 +458,19 @@ static long seccomp_attach_filter(unsign
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)
@@ -476,10 +481,8 @@ static inline void seccomp_filter_free(s
}
}

-/* 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;
@@ -488,6 +491,12 @@ void put_seccomp_filter(struct task_stru
}
}

+/* 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));
@@ -908,13 +917,13 @@ long seccomp_get_filter(struct task_stru
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:

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