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[86.26.103.58]) by smtp.googlemail.com with ESMTPSA id l20-20020a05600c089400b003a845621c5bsm661523wmp.34.2022.09.22.15.46.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 Sep 2022 15:46:33 -0700 (PDT) Message-ID: Date: Thu, 22 Sep 2022 23:46:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 1/3] misc: fastrpc: Fix use-after-free and race in fastrpc_map_find Content-Language: en-US To: Abel Vesa , Amol Maheshwari , Ekansh Gupta , Vamsi Krishna Gattupalli Cc: Arnd Bergmann , Greg Kroah-Hartman , linux-arm-msm@vger.kernel.org, Linux Kernel Mailing List , Ola Jeppsson References: <20220902151423.3351414-1-abel.vesa@linaro.org> From: Srinivas Kandagatla In-Reply-To: <20220902151423.3351414-1-abel.vesa@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On 02/09/2022 16:14, Abel Vesa wrote: > Currently, there is a race window between the point when the mutex is > unlocked in fastrpc_map_lookup and the reference count increasing > (fastrpc_map_get) in fastrpc_map_find, which can also lead to > use-after-free. > > So lets merge fastrpc_map_find into fastrpc_map_lookup which allows us > to both protect the maps list by also taking the &fl->lock spinlock and > the reference count, since the spinlock will be released only after. > Add take_ref argument to make this suitable for all callers. > > Fixes: 8f6c1d8c4f0c ("misc: fastrpc: Add fdlist implementation") > Co-developed-by: Ola Jeppsson > Signed-off-by: Ola Jeppsson > Signed-off-by: Abel Vesa > --- Reviewed-by: Srinivas Kandagatla > drivers/misc/fastrpc.c | 41 +++++++++++++++++++++-------------------- > 1 file changed, 21 insertions(+), 20 deletions(-) > > diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c > index 93ebd174d848..0c816a11eeec 100644 > --- a/drivers/misc/fastrpc.c > +++ b/drivers/misc/fastrpc.c > @@ -333,30 +333,31 @@ static void fastrpc_map_get(struct fastrpc_map *map) > > > static int fastrpc_map_lookup(struct fastrpc_user *fl, int fd, > - struct fastrpc_map **ppmap) > + struct fastrpc_map **ppmap, bool take_ref) > { > + struct fastrpc_session_ctx *sess = fl->sctx; > struct fastrpc_map *map = NULL; > + int ret = -ENOENT; > > - mutex_lock(&fl->mutex); > + spin_lock(&fl->lock); > list_for_each_entry(map, &fl->maps, node) { > - if (map->fd == fd) { > - *ppmap = map; > - mutex_unlock(&fl->mutex); > - return 0; > - } > - } > - mutex_unlock(&fl->mutex); > - > - return -ENOENT; > -} > + if (map->fd != fd) > + continue; > > -static int fastrpc_map_find(struct fastrpc_user *fl, int fd, > - struct fastrpc_map **ppmap) > -{ > - int ret = fastrpc_map_lookup(fl, fd, ppmap); > + if (take_ref) { > + ret = fastrpc_map_get(map); > + if (ret) { > + dev_dbg(sess->dev, "%s: Failed to get map fd=%d ret=%d\n", > + __func__, fd, ret); > + break; > + } > + } > > - if (!ret) > - fastrpc_map_get(*ppmap); > + *ppmap = map; > + ret = 0; > + break; > + } > + spin_unlock(&fl->lock); > > return ret; > } > @@ -703,7 +704,7 @@ static int fastrpc_map_create(struct fastrpc_user *fl, int fd, > struct fastrpc_map *map = NULL; > int err = 0; > > - if (!fastrpc_map_find(fl, fd, ppmap)) > + if (!fastrpc_map_lookup(fl, fd, ppmap, true)) > return 0; > > map = kzalloc(sizeof(*map), GFP_KERNEL); > @@ -1026,7 +1027,7 @@ static int fastrpc_put_args(struct fastrpc_invoke_ctx *ctx, > for (i = 0; i < FASTRPC_MAX_FDLIST; i++) { > if (!fdlist[i]) > break; > - if (!fastrpc_map_lookup(fl, (int)fdlist[i], &mmap)) > + if (!fastrpc_map_lookup(fl, (int)fdlist[i], &mmap, false)) > fastrpc_map_put(mmap); > } >