netdev - [PATCH bpf 2/2] bpf: fixes possible race in update_prog

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Message-Id: <20211026203825.2720459-3-eric.dumazet@gmail.com>
Date:   Tue, 26 Oct 2021 13:38:25 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        bpf <bpf@...r.kernel.org>
Subject: [PATCH bpf 2/2] bpf: fixes possible race in update_prog_stats() for 32bit arches

From: Eric Dumazet <edumazet@...gle.com>

It seems update_prog_stats() suffers from same issue fixed
in the prior patch:

As it can run while interrupts are enabled, it could
be re-entered and the u64_stats syncp could be mangled.

Fixes: fec56f5890d9 ("bpf: Introduce BPF trampoline")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>
---
 kernel/bpf/trampoline.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index fe1e857324e6683cecf5f88d24e0790f7ec72253..d3a307a8c42b95692f082f23f01e1ed470e63dec 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -585,11 +585,13 @@ static void notrace update_prog_stats(struct bpf_prog *prog,
 	     * Hence check that 'start' is valid.
 	     */
 	    start > NO_START_TIME) {
+		unsigned long flags;
+
 		stats = this_cpu_ptr(prog->stats);
-		u64_stats_update_begin(&stats->syncp);
+		flags = u64_stats_update_begin_irqsave(&stats->syncp);
 		stats->cnt++;
 		stats->nsecs += sched_clock() - start;
-		u64_stats_update_end(&stats->syncp);
+		u64_stats_update_end_irqrestore(&stats->syncp, flags);
 	}
 }
 
-- 
2.33.0.1079.g6e70778dc9-goog