linux-kernel - [PATCH] perf: Fix data race between pin

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210527104711.2671610-1-elver@google.com>
Date:   Thu, 27 May 2021 12:47:11 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, peterz@...radead.org, mingo@...hat.com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     kasan-dev@...glegroups.com, dvyukov@...gle.com,
        syzbot+142c9018f5962db69c7e@...kaller.appspotmail.com
Subject: [PATCH] perf: Fix data race between pin_count increment/decrement

KCSAN reports a data race between increment and decrement of pin_count:

  write to 0xffff888237c2d4e0 of 4 bytes by task 15740 on cpu 1:
   find_get_context		kernel/events/core.c:4617
   __do_sys_perf_event_open	kernel/events/core.c:12097 [inline]
   __se_sys_perf_event_open	kernel/events/core.c:11933
   ...
  read to 0xffff888237c2d4e0 of 4 bytes by task 15743 on cpu 0:
   perf_unpin_context		kernel/events/core.c:1525 [inline]
   __do_sys_perf_event_open	kernel/events/core.c:12328 [inline]
   __se_sys_perf_event_open	kernel/events/core.c:11933
   ...

Because neither read-modify-write here is atomic, this can lead to one of the
operations being lost, resulting in an inconsistent pin_count. Fix it by adding
the missing locking in the CPU-event case.

Reported-by: syzbot+142c9018f5962db69c7e@...kaller.appspotmail.com
Signed-off-by: Marco Elver <elver@...gle.com>
---
 kernel/events/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6fee4a7e88d7..fe88d6eea3c2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4609,7 +4609,9 @@ find_get_context(struct pmu *pmu, struct task_struct *task,
 		cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
 		ctx = &cpuctx->ctx;
 		get_ctx(ctx);
+		raw_spin_lock_irqsave(&ctx->lock, flags);
 		++ctx->pin_count;
+		raw_spin_unlock_irqrestore(&ctx->lock, flags);

 		return ctx;
 	}
-- 
2.31.1.818.g46aad6cb9e-goog