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Subject[PATCH v2] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get_filter()
Date
From: Oleg Nesterov <oleg@redhat.com>

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 <chrissalls5@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Tycho Andersen <tycho@docker.com>
---
kernel/seccomp.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index c24579dfa7a1..bb3a38005b9c 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -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
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