From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 613593D3319 for ; Mon, 4 May 2026 12:33:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777897989; cv=none; b=dWDej1xHXbRgQLpECu4FMnmbwGk1RtdRYa0ftELIuKUG0ZJRZ/vSU93Rhq8sYUzn3eBJMc+RTIr9xGMX6fwTnwy45VfaDTGTbfSRv0XgMcic2K5TnCYHNiMt5sT8iEgTkK/fPNldDDf410qgTk+vLkhsDSUUFF5tuUayVXDx2nY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777897989; c=relaxed/simple; bh=yBqzeljeCYAWMfvKpILNF3nSvYdFoDwPi6LXBX0tD48=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=jVJlwagW2uGTrfZ95npdHqogJf8k4CmVvBHj4KnvmGmRoKwUB9vUU8WQ2zLXqlcQQj1gWbUccnCPdEjvit/tDQk5OlHIVkuUaUgEOtVoKEzhfBKcjt4XTNBYA3wVWdaKGdC4ZQKIdpEflpg5dR/xcf3UKtjOWGuzqXzUJgkecPM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--richardycc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=DKQwjQRb; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--richardycc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="DKQwjQRb" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-835423c69ffso550364b3a.1 for ; Mon, 04 May 2026 05:33:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1777897988; x=1778502788; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=e8/CDtnGvalUzgGFzgyiRHcKrsHnUrOiavCD5LiN7Ac=; b=DKQwjQRbrBKyaP29/7VWl0cRhivrxZq/Z+93tXrAr0iamjMNRA2P1BvvSVer56ErC1 +yPIhyPzP96lA0Ojv1biVLaNXBziRBJ+YWNg83uqocBgi25ZYOPo07I1IDPDAVj6da/5 Rpej3IomOvrf5iJz8tTqODt4ejklGo0zj051JoAai0POboLQXRnnY4ohUt6l0ZU9d4kv Wh2Fxd1BC6Atx0mhsZO5uK83pEIUZRSuZKOEJuNRkEJLf69bbevv9ibRxRwWBQYw5hQl YugcfCiS4CBSdB5HBu8BSnMywUQzbNW1hdsQigNyOIcVnhWm4u74KVWn0vma163GYDEF rN9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777897988; x=1778502788; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=e8/CDtnGvalUzgGFzgyiRHcKrsHnUrOiavCD5LiN7Ac=; b=nAy7SOHdiCfrlsxZrLKIVbNmF+cGXIBfc/Ccn0PAK6BxsVDyeuDIJV1cDgKGLc4osV u8F2eSmH2+xp34KlsRzDPXsc8iezxNx8+hBHkwYfk8a+DF0t5eEdR7uWWd/VLc55CL9b GOnPh2A6kw6j7F9kUUpA1RqklS0P/wI/vE/jG7VEi25tevfB4y9vnfry75EjHwdvLkHu TRrIDRGuIn3Bm9ESBy7at4K+GnrDAQF+WMW0xdMA/FTgeJDV7YJlKPY1PP/HVzd+/Qa/ hmF0KBw76pM7Y06MyASKwUVlk5Q/QleXA2R0rSM9WFNb76MpeeMTB88etuw81PKGgHBl HR8A== X-Forwarded-Encrypted: i=1; AFNElJ94W7u6mhbm1E3B5xJpM7TblHyHWgLRJSVMwhCZoSG5hRHoCz/gqjwpDE7XQodfoaGS8iESde4yqnUGwQ==@vger.kernel.org X-Gm-Message-State: AOJu0Yz/VbDDS9tG09hxUyILqNtrEgc6CsF90/kChcpDLU7Brrkve9dK KQ245oxCVma0kgkCC20ulq+MNHnjeZwULsAsQB79+BgGxbluOQdjVYOmm7GABdN3xljR7MMzud+ bos8EFrx06l9puxMlHrv5 X-Received: from pfblu21.prod.google.com ([2002:a05:6a00:7495:b0:82f:86c3:55ba]) (user=richardycc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:8ccb:b0:835:3c9f:1a15 with SMTP id d2e1a72fcca58-8353c9f1f13mr4332851b3a.25.1777897987531; Mon, 04 May 2026 05:33:07 -0700 (PDT) Date: Mon, 4 May 2026 12:32:30 +0000 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.54.0.545.g6539524ca2-goog Message-ID: <20260504123230.3833765-1-richardycc@google.com> Subject: [PATCH] zram: fix use-after-free in zram_writeback_endio From: Richard Chang To: Minchan Kim , Sergey Senozhatsky , Jens Axboe , Andrew Morton Cc: bgeffon@google.com, liumartin@google.com, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-mm@kvack.org, Richard Chang Content-Type: text/plain; charset="UTF-8" A crash was observed in zram_writeback_endio due to a NULL pointer dereference in wake_up. The root cause is a race condition between the bio completion handler (zram_writeback_endio) and the writeback task. In zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after releasing wb_ctl->done_lock. This creates a race window where the writeback task can see num_inflight become 0, return, and free wb_ctl before zram_writeback_endio calls wake_up(). CPU 0 (zram_writeback_endio) CPU 1 (zram_complete_done_reqs) ============================ ============================ spin_lock(&wb_ctl->done_lock); list_add(&req->entry, &wb_ctl->done_reqs); spin_unlock(&wb_ctl->done_lock); while (&wb_ctl->num_inflight) > 0) spin_lock(&wb_ctl->done_lock); list_del(&req->entry); spin_unlock(&wb_ctl->done_lock); // num_inflight becomes 0 atomic_dec(&wb_ctl->num_inflight); returns to writeback_store(); // frees wb_ctl release_wb_ctl(wb_ctl); // UAF crash! wake_up(&wb_ctl->done_wait); Fix this by moving wake_up() inside the done_lock critical section. This ensures that zram_complete_done_reqs cannot consume the request and decrement num_inflight until zram_writeback_endio has finished calling wake_up() and released the lock. Fixes: f405066a1f0d ("zram: introduce writeback bio batching") Signed-off-by: Richard Chang --- drivers/block/zram/zram_drv.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index aebc710f0d6a..a457fdf564f8 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -966,9 +966,8 @@ static void zram_writeback_endio(struct bio *bio) spin_lock_irqsave(&wb_ctl->done_lock, flags); list_add(&req->entry, &wb_ctl->done_reqs); - spin_unlock_irqrestore(&wb_ctl->done_lock, flags); - wake_up(&wb_ctl->done_wait); + spin_unlock_irqrestore(&wb_ctl->done_lock, flags); } static void zram_submit_wb_request(struct zram *zram, -- 2.54.0.545.g6539524ca2-goog