linux-kernel - Re: eBPF / seccomp globals?

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Message-ID: <CAMkWEXMm=vRoxyzfODQsg9kvMfYs9ENw=dn+2cvPMP-i7_WzZg@mail.gmail.com>
Date:	Thu, 10 Sep 2015 23:22:23 +0000
From:	Michael Tirado <mtirado418@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: eBPF / seccomp globals?

Sorry for spamming you guys with my ugly, poorly formatted hack.
I had to change something due to my shallow knowledge of how
multiprocessors / multiple threads sharing a filter would behave.
There may have been a possibility for the deferred integer to rollover
and ruin everything?  just in case someone tries to use it....

From: Michael R Tirado <mtirado418@...il.com>
Date: Thu, 10 Sep 2015 23:06:55 +0000
Subject: [PATCH 2/2] changed to signed integer, due to multiprocesor
 uncertainty.

---
 kernel/seccomp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index dc2a5af..e39e8c2 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -58,7 +58,7 @@ struct seccomp_filter {
     atomic_t usage;
     struct seccomp_filter *prev;
     struct bpf_prog *prog;
-    unsigned int deferred;
+    int deferred;
 };

 /* Limit any path through the tree to 256KB worth of instructions. */
@@ -198,7 +198,7 @@ static u32 seccomp_run_filters(struct seccomp_data *sd)
      */
     for (; f; f = f->prev) {
         u32 cur_ret;
-        if (unlikely(f->deferred)) {
+        if (unlikely(f->deferred > 0)) {
             --f->deferred;
             continue;
         }
-- 
1.8.4
--
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