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 52EED2D8DDF; Fri, 22 May 2026 02:06:58 +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=1779415619; cv=none; b=sr17l3eXH10RIagJLyc/coQJcMRgStPkYd8XWv2rteDzb+FztF67spLKlrVaqBDU6AUMYqyCnRFFtcUopsQ3PrjhGLssJ8OJQ052vb2YCjjxxh/s0eArkd2Ne2bBd7mLX9dVUcptMDzhFxWENWI/2ZlsTMfWERQN0RYEsq6ecis= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779415619; c=relaxed/simple; bh=v2H2gPm13rZITG5qaRb54LWDslrNiIa4cv9+eIAOl5g=; h=Date:To:From:Subject:Message-Id; b=Ao2Nfk3loDlH7HRrryzIRMCebS3/lsQ0RnprqlzR1mQHWhhpqJXnZ2hteSLnSu1KZrxj7E0z5krpv+xdeIC94tEZIk9I4bPdunB4r9lHZImA2xiu26mvZeBpb096jJkNWQ+UxpFSeikZHjLONCcgM4hrAW3YURmtc5Z5se1taFI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Ye7ZSdgH; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Ye7ZSdgH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 271FD1F000E9; Fri, 22 May 2026 02:06:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1779415618; bh=FnvqrIaHgVQBpXX6/CL1m0NWjTrNoxymKaKMcW77u78=; h=Date:To:From:Subject; b=Ye7ZSdgHri4pdCxd7OSIKckspOSugh5lPypG+lvGamJ/oe9E+OE92YOFlLaDFBQAO o+HdEyAwoQFvRuW21uym1Y6berpnMGLtOAl/P/i1hQg5DYpFICxJvcvVMGfoaschnS O0bM4EJBV+ugfnpv7H9t1iUtI27DnN6vyCsL+9oc= Date: Thu, 21 May 2026 19:06:57 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,senozhatsky@chromium.org,minchan@kernel.org,liumartin@google.com,bgeffon@google.com,axboe@kernel.dk,a929244872@163.com,richardycc@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] zram-fix-use-after-free-in-zram_writeback_endio.patch removed from -mm tree Message-Id: <20260522020658.271FD1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: zram: fix use-after-free in zram_writeback_endio has been removed from the -mm tree. Its filename was zram-fix-use-after-free-in-zram_writeback_endio.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Richard Chang Subject: zram: fix use-after-free in zram_writeback_endio Date: Tue, 12 May 2026 07:49:18 +0000 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 (writeback_store) ============================ ============================ zram_writeback_slots zram_submit_wb_request zram_submit_wb_request wait_event(wb_ctl->done_wait) spin_lock(&wb_ctl->done_lock); list_add(&req->entry, &wb_ctl->done_reqs); spin_unlock(&wb_ctl->done_lock); wake_up(&wb_ctl->done_wait); 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 (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(num_inflight); // Leave zram_writeback_slots // Free wb_ctl release_wb_ctl(wb_ctl); // UAF crash! wake_up(&wb_ctl->done_wait); This patch fixes this race by using RCU. By protecting wb_ctl with rcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it, we ensure that wb_ctl remains valid during the execution of zram_writeback_endio. Link: https://lore.kernel.org/20260512074918.2606208-1-richardycc@google.com Fixes: f405066a1f0d ("zram: introduce writeback bio batching") Signed-off-by: Richard Chang Suggested-by: Sergey Senozhatsky Suggested-by: Minchan Kim Acked-by: Sergey Senozhatsky Acked-by: Minchan Kim Cc: Brian Geffon Cc: Jens Axboe Cc: Martin Liu Cc: wang wei Cc: Signed-off-by: Andrew Morton --- drivers/block/zram/zram_drv.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/drivers/block/zram/zram_drv.c~zram-fix-use-after-free-in-zram_writeback_endio +++ a/drivers/block/zram/zram_drv.c @@ -33,6 +33,7 @@ #include #include #include +#include #include "zram_drv.h" @@ -504,6 +505,7 @@ struct zram_wb_ctl { wait_queue_head_t done_wait; spinlock_t done_lock; atomic_t num_inflight; + struct rcu_head rcu; }; struct zram_wb_req { @@ -847,7 +849,7 @@ static void release_wb_ctl(struct zram_w release_wb_req(req); } - kfree(wb_ctl); + kfree_rcu(wb_ctl, rcu); } static struct zram_wb_ctl *init_wb_ctl(struct zram *zram) @@ -964,11 +966,13 @@ static void zram_writeback_endio(struct struct zram_wb_ctl *wb_ctl = bio->bi_private; unsigned long flags; + rcu_read_lock(); 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); + rcu_read_unlock(); } static void zram_submit_wb_request(struct zram *zram, _ Patches currently in -mm which might be from richardycc@google.com are