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Thu, 05 Nov 2026 08:56:21 -0800 (PST) Received: from p14s ([2604:3d09:148c:c800:c7a9:fa1d:b267:7419]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ed09127905sm20286145ad.48.2026.11.05.08.56.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 08:56:21 -0800 (PST) Date: Thu, 5 Nov 2026 10:56:19 -0600 From: Mathieu Poirier To: Yu Zhang Cc: Bjorn Andersson , linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] rpmsg: char: take ept_lock in the SET_INCOMING_FLOWCONTROL ioctl Message-ID: References: <20261026100306.68019-1-yuz08559@gmail.com> <20261031090650.23701-1-yuz08559@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261031090650.23701-1-yuz08559@gmail.com> On Sat, Oct 31, 2026 at 07:06:50PM +1000, Yu Zhang wrote: > rpmsg_eptdev_ioctl() handles RPMSG_SET_INCOMING_FLOWCONTROL by calling > rpmsg_set_flow_control(eptdev->ept, ...) without holding eptdev->ept_lock > and without checking eptdev->ept for NULL. rpmsg_set_flow_control() > dereferences ept->ops, so this is the only eptdev->ept user that does not > honour the ept_lock discipline. > > eptdev->ept is torn down under ept_lock: rpmsg_chrdev_eptdev_destroy() > (reached via RPMSG_DESTROY_EPT_IOCTL on a second fd, or when the rpmsg > device is removed) and rpmsg_eptdev_release() both do > > mutex_lock(&eptdev->ept_lock); > rpmsg_destroy_ept(eptdev->ept); > eptdev->ept = NULL; > mutex_unlock(&eptdev->ept_lock); > > and rpmsg_destroy_ept() drops the endpoint's last reference and frees it. > A SET_INCOMING_FLOWCONTROL ioctl running concurrently can therefore read > eptdev->ept just as it is freed and dereference ept->ops -> use-after-free > (or a NULL dereference once ept has been cleared). > > Fixes: 5550201c0fe2 ("rpmsg: char: Add RPMSG GET/SET FLOWCONTROL IOCTL support") > Cc: stable@vger.kernel.org > Signed-off-by: Yu Zhang > --- > v2: > - Drop the paragraph about the other ept_lock users from the commit > message (Mathieu). > - Bail out early when the endpoint is already gone instead of an > if/else around the call (Mathieu). > v1: https://lore.kernel.org/all/20261026100306.68019-1-yuz08559@gmail.com/ > --- > drivers/rpmsg/rpmsg_char.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > Applied. Thanks, Mathieu > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c > index 550fda2..d8868fa 100644 > --- a/drivers/rpmsg/rpmsg_char.c > +++ b/drivers/rpmsg/rpmsg_char.c > @@ -343,7 +343,20 @@ static long rpmsg_eptdev_ioctl(struct file *fp, unsigned int cmd, > break; > } > set = !!arg; > - ret = rpmsg_set_flow_control(eptdev->ept, set, eptdev->chinfo.dst); > + > + ret = mutex_lock_interruptible(&eptdev->ept_lock); > + if (ret) > + break; > + > + if (!eptdev->ept) { > + mutex_unlock(&eptdev->ept_lock); > + ret = -EPIPE; > + break; > + } > + > + ret = rpmsg_set_flow_control(eptdev->ept, set, > + eptdev->chinfo.dst); > + mutex_unlock(&eptdev->ept_lock); > break; > case RPMSG_DESTROY_EPT_IOCTL: > /* Don't allow to destroy a default endpoint. */ > -- > 2.43.0 >