From nobody Thu Apr 2 23:53:37 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 A425A374721 for ; Thu, 26 Mar 2026 10:46:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774521985; cv=none; b=Nh3qJ+bp7/tgy9qn+LYqBQRKDWfh6fCfQHubQfX2pqz3SbWck6wEDfKBL++VmVni+Fs69UWYhwsb0wfgtGmkPdl9lEBa1SeuFVEqMYLC9XTfUUSPXT8kEqsSBrZ2R91ku3ucnJwkGJU5Mh+Ya0ehU2PSDzQ8TgxqrU6HK6aLCb4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774521985; c=relaxed/simple; bh=V4fOTRTogYEpBNmIJVKnkZTFC5/VLtjae4HU+6Q4TwE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LT8rLr8wnPOTNSaNU1Pz8o4x09sgGqogtnOFaDPsrNS4GMLI65aviMhIWyXsY840uO7GMg/wrXvjO+iMwgWNQex4LQzFbNPSTUhA19d1OQ2AcbT9C5idfRs1yrI/qWeiou3EHogQM/0rOw/DSUN37xF9QYgIK/wreuRGlef2OKU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=fDj6xJtm; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="fDj6xJtm" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774521982; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ikME2fKnQmyL6ccsVR9iuIqF4Gk7rE38Es/pzWOmTZE=; b=fDj6xJtm/N4+mEoHE3Ot/4nj1rIvAkUjzm5xDVpkMklyTUn9dT2YmukaWCszz8vkKWmccp PX/OMy1ynxsrn0WAbi6snzNZK6PS11qX/fP1zC8POHrjBxaost4KV9oUZBvM7mAm6CFlS9 4pPRMKh+7LNovGqCQK2JZXsdlJ0WwFo= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-365-ZuIOung0PmK_T8_--PBq-A-1; Thu, 26 Mar 2026 06:46:19 -0400 X-MC-Unique: ZuIOung0PmK_T8_--PBq-A-1 X-Mimecast-MFC-AGG-ID: ZuIOung0PmK_T8_--PBq-A_1774521975 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AE5CD19560B6; Thu, 26 Mar 2026 10:46:13 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.44.33.121]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id CF2E618002A6; Thu, 26 Mar 2026 10:46:04 +0000 (UTC) From: David Howells To: Christian Brauner , Matthew Wilcox , Christoph Hellwig Cc: David Howells , Paulo Alcantara , Jens Axboe , Leon Romanovsky , Steve French , ChenXiaoSong , Marc Dionne , Eric Van Hensbergen , Dominique Martinet , Ilya Dryomov , Trond Myklebust , netfs@lists.linux.dev, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs@lists.linux.dev, linux-erofs@lists.ozlabs.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+7227db0fbac9f348dba0@syzkaller.appspotmail.com, Deepanshu Kartikey Subject: [PATCH 01/26] netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry Date: Thu, 26 Mar 2026 10:45:16 +0000 Message-ID: <20260326104544.509518-2-dhowells@redhat.com> In-Reply-To: <20260326104544.509518-1-dhowells@redhat.com> References: <20260326104544.509518-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Content-Type: text/plain; charset="utf-8" From: Deepanshu Kartikey When a write subrequest is marked NETFS_SREQ_NEED_RETRY, the retry path in netfs_unbuffered_write() unconditionally calls stream->prepare_write() without checking if it is NULL. Filesystems such as 9P do not set the prepare_write operation, so stream->prepare_write remains NULL. When get_user_pages() fails with -EFAULT and the subrequest is flagged for retry, this results in a NULL pointer dereference at fs/netfs/direct_write.c:189. Fix this by mirroring the pattern already used in write_retry.c: if stream->prepare_write is NULL, skip renegotiation and directly reissue the subrequest via netfs_reissue_write(), which handles iterator reset, IN_PROGRESS flag, stats update and reissue internally. Fixes: a0b4c7a49137 ("netfs: Fix unbuffered/DIO writes to dispatch subreque= sts in strict sequence") Reported-by: syzbot+7227db0fbac9f348dba0@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D7227db0fbac9f348dba0 Signed-off-by: Deepanshu Kartikey Signed-off-by: David Howells Reviewed-by: Paulo Alcantara (Red Hat) --- fs/netfs/direct_write.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c index dd1451bf7543..4d9760e36c11 100644 --- a/fs/netfs/direct_write.c +++ b/fs/netfs/direct_write.c @@ -186,10 +186,18 @@ static int netfs_unbuffered_write(struct netfs_io_req= uest *wreq) stream->sreq_max_segs =3D INT_MAX; =20 netfs_get_subrequest(subreq, netfs_sreq_trace_get_resubmit); - stream->prepare_write(subreq); =20 - __set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags); - netfs_stat(&netfs_n_wh_retry_write_subreq); + if (stream->prepare_write) { + stream->prepare_write(subreq); + __set_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags); + netfs_stat(&netfs_n_wh_retry_write_subreq); + } else { + struct iov_iter source; + + netfs_reset_iter(subreq); + source =3D subreq->io_iter; + netfs_reissue_write(stream, subreq, &source); + } } =20 netfs_unbuffered_write_done(wreq);