From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 D08ED314B63; Wed, 13 May 2026 02:56:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778640960; cv=none; b=mejUGF1y7I6Aamps4VC/teZN26GnlRHde/DVlrAzhaSI43lNMdRcvyyneIR56GMFmWBc7B/EduIPcb7dIGyPTL65z0wRfuisTtzcGK6z4qWzZzHpvNq1KHTH5oVFjO+VUqw67KWNrYhyGbY9ZPcnRJqJAtrzJmUIFDis0dVZSb0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778640960; c=relaxed/simple; bh=xmbP2ZRR7oNJJfF6MEuwvtZUdx9LzlwAAsLx2mdK7nY=; h=Date:To:From:Subject:Message-Id; b=eFn1ZYl3BsTNQEFGv7mkmMNZfgY5j6mw7L03j96dASCDF7TttEe0L2nN+t7FZHbPZK7YaNyEeFWmhZ5Rhr7e+pKMlOUhSPUkA4HeH7pZWDjqvPTBjbhdP8OvNNLtwwObVEGmkPVuIBcB+EZiG5i0tEIfbMrrvEVyiwtyYH4Ho34= 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=lVihkmXD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="lVihkmXD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 78696C2BCB8; Wed, 13 May 2026 02:56:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1778640960; bh=xmbP2ZRR7oNJJfF6MEuwvtZUdx9LzlwAAsLx2mdK7nY=; h=Date:To:From:Subject:From; b=lVihkmXDh86IDbTRfoxWPiRMCLh0PSduciQcAy6N+eSIeDB2sZO36NfkgNDMOspG0 EjiGNTteuJDZFALpk4xDjwqGf641qP4b+zEoJOpgt7CpFqILXY5ylywjlj9AJtgpuI +Y6u/MhV0FR0ZDIqtEW+OksJDVIRMQpaCLY55ocE= Date: Tue, 12 May 2026 19:55:59 -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,richardycc@google.com,akpm@linux-foundation.org From: Andrew Morton Subject: + zram-fix-use-after-free-in-zram_writeback_endio.patch added to mm-hotfixes-unstable branch Message-Id: <20260513025600.78696C2BCB8@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: zram: fix use-after-free in zram_writeback_endio has been added to the -mm mm-hotfixes-unstable branch. Its filename is zram-fix-use-after-free-in-zram_writeback_endio.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/zram-fix-use-after-free-in-zram_writeback_endio.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ 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: 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 zram-fix-use-after-free-in-zram_writeback_endio.patch