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[62.99.137.214]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43796acf5b9sm49037171f8f.34.2026.02.19.06.53.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Feb 2026 06:53:54 -0800 (PST) Message-ID: <2b87cbab-49e2-4290-8784-b771e90e016f@linbit.com> Date: Thu, 19 Feb 2026 15:53:53 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drbd: fix a null-pointer dereference when the request event in drbd_request_endio() is READ_COMPLETED_WITH_ERROR To: Tuo Li , philipp.reisner@linbit.com, lars.ellenberg@linbit.com, axboe@kernel.dk Cc: drbd-dev@lists.linbit.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260104165355.151864-1-islituo@gmail.com> Content-Language: en-US From: =?UTF-8?Q?Christoph_B=C3=B6hmwalder?= In-Reply-To: <20260104165355.151864-1-islituo@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/4/26 17:53, Tuo Li wrote: > In drbd_request_endio(), the request event what can be set to > READ_COMPLETED_WITH_ERROR. In this case, __req_mod() is invoked with a NULL > peer_device: > > __req_mod(req, what, NULL, &m); > > When handling READ_COMPLETED_WITH_ERROR, __req_mod() unconditionally calls > drbd_set_out_of_sync(): > > case READ_COMPLETED_WITH_ERROR: > drbd_set_out_of_sync(peer_device, req->i.sector, req->i.size); > > The drbd_set_out_of_sync() macro expands to __drbd_change_sync(): > > #define drbd_set_out_of_sync(peer_device, sector, size) \ > __drbd_change_sync(peer_device, sector, size, SET_OUT_OF_SYNC) > > However, __drbd_change_sync() assumes a valid peer_device and immediately > dereferences it: > > struct drbd_device *device = peer_device->device; > > If peer_device is NULL, this results in a NULL-pointer dereference. > > Fix this by adding a NULL check in __req_mod() before calling > drbd_set_out_of_sync(). Thank you for the report and patch. The bug analysis is correct, but the fix is not. > > Signed-off-by: Tuo Li > --- > drivers/block/drbd/drbd_req.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c > index d15826f6ee81..aa3da2733f14 100644 > --- a/drivers/block/drbd/drbd_req.c > +++ b/drivers/block/drbd/drbd_req.c > @@ -621,7 +621,8 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what, > break; > > case READ_COMPLETED_WITH_ERROR: > - drbd_set_out_of_sync(peer_device, req->i.sector, req->i.size); > + if (peer_device) > + drbd_set_out_of_sync(peer_device, req->i.sector, req->i.size); > drbd_report_io_error(device, req); > __drbd_chk_io_error(device, DRBD_READ_ERROR); > fallthrough; In this code path, peer_device is *always* NULL -- the only caller that sets READ_COMPLETED_WITH_ERROR is drbd_request_endio(), which always passes NULL for peer_device. So this NULL check effectively turns the drbd_set_out_of_sync() call into dead code. Silently skipping the call here means we lose out-of-sync tracking for local read errors, which is a data consistency problem. The proper fix is to obtain the peer_device via first_peer_device(device), like in a similar path in drbd_req_destroy (drbd_req.c:125). case READ_COMPLETED_WITH_ERROR: drbd_set_out_of_sync(first_peer_device(device), req->i.sector, req->i.size); Regards, Christoph -- Christoph Böhmwalder LINBIT | Keeping the Digital World Running DRBD HA — Disaster Recovery — Software defined Storage