linux-kernel - [PATCH 2/6] seccomp: make underlying bpf ref counted as well

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Message-Id: <1441382664-17437-3-git-send-email-tycho.andersen@canonical.com>
Date:	Fri,  4 Sep 2015 10:04:20 -0600
From:	Tycho Andersen <tycho.andersen@...onical.com>
To:	Kees Cook <keescook@...omium.org>,
	Alexei Starovoitov <ast@...nel.org>
Cc:	Will Drewry <wad@...omium.org>, Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Tycho Andersen <tycho.andersen@...onical.com>
Subject: [PATCH 2/6] seccomp: make underlying bpf ref counted as well

In the next patch, we're going to add a way to access the underlying
filters via bpf fds. This means that we need to ref-count both the
struct seccomp_filter objects and the struct bpf_prog objects separately,
in case a process dies but a filter is still referred to by another
process.

Additionally, we mark classic converted seccomp filters as seccomp eBPF
programs, since they are a subset of what is supported in seccomp eBPF.

Signed-off-by: Tycho Andersen <tycho.andersen@...onical.com>
CC: Kees Cook <keescook@...omium.org>
CC: Will Drewry <wad@...omium.org>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Pavel Emelyanov <xemul@...allels.com>
CC: Serge E. Hallyn <serge.hallyn@...ntu.com>
CC: Alexei Starovoitov <ast@...nel.org>
CC: Daniel Borkmann <daniel@...earbox.net>
---
 kernel/seccomp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 5bd4779..acfe1fb 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -377,6 +377,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 	}
 
 	atomic_set(&sfilter->usage, 1);
+	atomic_set(&sfilter->prog->aux->refcnt, 1);
+	sfilter->prog->type = BPF_PROG_TYPE_SECCOMP;
 
 	return sfilter;
 }
@@ -469,7 +471,7 @@ void get_seccomp_filter(struct task_struct *tsk)
 static inline void seccomp_filter_free(struct seccomp_filter *filter)
 {
 	if (filter) {
-		bpf_prog_free(filter->prog);
+		bpf_prog_put(filter->prog);
 		kfree(filter);
 	}
 }
-- 
2.1.4

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