From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 29F5541D11C; Sat, 12 Sep 2026 09:33:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789205628; cv=none; b=ehXXGGWoIx4LgLoP9TbuRYIM9SXTFElR9/o3S1aeYSNjlU8kLAzhl35Ug+EGDjlvi2r7PCu0nBw2McLKZYppRcUawJdf8nyAy/XaYTfIA8JhTici9O4F4Edcc1xCKmwl4wpkJT9njcWi4NEovqyBqLY+ur2Dta86RpuuvIkEvGY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789205628; c=relaxed/simple; bh=tOdTRJu6FAJWay53JcPKJWqIdDUwdjEPjYfTOiJAtjs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GwjgJmcy0v3J/nzdZRUBFYwgHtei0wnGBQFWi4K5bwt2tWTodFvJaGcUY55f5MIvarVHoGc7T327KNPQOqwXSgxXmLhvZsBmtGzdWBigXTq3zsncAGsfp/6JUAQFMy1ieqVjIJj9XyM9+jYuJfEqFAn249v9zywNrmWGSFEIWyU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=17dud6Ek; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="17dud6Ek" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C9F801F000FF; Sat, 12 Sep 2026 09:33:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789205625; bh=xkqg26ror/UVmymsZr58LhUjVicuIXf+ubCDPBQJvt8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=17dud6EkPuTtwMtv6pck6Mk/WWMufjo8i6mwCFYh1A8/BMpt9PcjdcYKgKHu7voIL 7I9AW9s9+cJcgDXeq6apZtWW5STwavk3jRtnlEA1RR64ont7XHYBZXiMqy7KxRwmXZ AOtvG6o50V4UGCj6Ls+Q2sDpOTSxD1/Yug7pdsW8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kimi Security Team , Peter Zijlstra , Weiming Shi , Yilin Zhang , Sasha Levin Subject: [PATCH 6.18 0039/1518] perf: Fix use-after-free when perf mmap() revival races with the last munmap() Date: Sat, 12 Sep 2026 08:36:48 +0200 Message-ID: <20260912065624.316408122@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065623.398859879@linuxfoundation.org> References: <20260912065623.398859879@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Yilin Zhang [ Upstream commit 58a8108bc73de0740d5b88150465d6690ea5f85f ] perf_mmap_close() drops rb->mmap_count *without* holding event->mmap_mutex (the refcount_dec_and_test() right before the refcount_dec_and_mutex_lock() of event->mmap_count). A concurrent perf_mmap_rb() can slot its entire "revival" path into that window (perf_mmap holds event->mmap_mutex for its whole duration, including rb_alloc): munmap side (perf_mmap_close) mmap side (perf_mmap_rb) ----------------------------------- -------------------------------- rb->mmap_count 1 -> 0 (no lock) (holds event->mmap_mutex) inc_not_zero(rb->mmap_count) fails ring_buffer_attach(event, NULL) rb_alloc() + attach new rb refcount_set(&event->mmap_count, 1) lock; event->mmap_count 1 -> 0 ring_buffer_attach(event, NULL) ring_buffer_put() -> frees the *new* rb The revival's refcount_set(&event->mmap_count, 1) is an invisible 1 -> 1 write: the close frees the just-revived buffer although the other process still has it mapped -- a page-level use-after-free allowing local privilege escalation to root by any unprivileged user (default kernel.perf_event_paranoid=2). Swap the order of the two counter updates: event->mmap_count is dropped first via refcount_dec_and_mutex_lock(), so its 1 -> 0 transition and the ring_buffer_attach() stay serialized with perf_mmap(). rb->mmap_count == 0 then implies every event using the buffer is detached already, so the result of the rb->mmap_count drop can gate the remaining teardown directly and detach_rest is no longer needed. An earlier fix for this race from Kyle Zeng and David Lee takes event->mmap_mutex around both counter updates [0]; here the not-last close stays lockless. Fixes: 59741451b49c ("perf: Identify the 0->1 transition for event::mmap_count") Reported-by: Kimi Security Team Suggested-by: Peter Zijlstra Co-developed-by: Weiming Shi Signed-off-by: Weiming Shi Signed-off-by: Yilin Zhang Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/linux-perf-users/20260804060931.711308-1-david.lee@trailofbits.com/ [0] Cc: Cc: stable@vger.kernel.org # 6.18+ Link: https://patch.msgid.link/20260831162155.1437652-1-yilinzhang@moonshot.ai Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/events/core.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6753,7 +6753,6 @@ static void perf_mmap_close(struct vm_ar mapped_f unmapped = get_mapped(event, event_unmapped); struct perf_buffer *rb = ring_buffer_get(event); struct user_struct *mmap_user = rb->mmap_user; - bool detach_rest = false; /* FIXIES vs perf_pmu_unregister() */ if (unmapped) @@ -6784,17 +6783,18 @@ static void perf_mmap_close(struct vm_ar mutex_unlock(&rb->aux_mutex); } - if (refcount_dec_and_test(&rb->mmap_count)) - detach_rest = true; - - if (!refcount_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) - goto out_put; - - ring_buffer_attach(event, NULL); - mutex_unlock(&event->mmap_mutex); + /* + * Drop references in reverse order of perf_mmap() to prevent + * rb revival after rb->mmap_count reaches zero. + */ + if (refcount_dec_and_mutex_lock(&event->mmap_count, + &event->mmap_mutex)) { + ring_buffer_attach(event, NULL); + mutex_unlock(&event->mmap_mutex); + } /* If there's still other mmap()s of this buffer, we're done. */ - if (!detach_rest) + if (!refcount_dec_and_test(&rb->mmap_count)) goto out_put; /*