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Message-ID: <20231021-strncpy-drivers-rpmsg-virtio_rpmsg_bus-c-v1-1-8abb919cbe24@google.com> Date: Sat, 21 Oct 2023 00:09:16 +0000 From: Justin Stitt <justinstitt@...gle.com> To: Bjorn Andersson <andersson@...nel.org>, Mathieu Poirier <mathieu.poirier@...aro.org> Cc: linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com> Subject: [PATCH] rpmsg: virtio: replace deprecated strncpy with strscpy/_pad strncpy() is deprecated for use on NUL-terminated destination strings [1] and as such we should prefer more robust and less ambiguous string interfaces. This patch replaces 3 callsites of strncpy(). The first two populate the destination buffer `nsm.name` -- which we expect to be NUL-terminated based on their use with format strings. Firstly, as I understand it, virtio_rpmsg_announce_create() creates an rpmsg_ns_msg and sends via: virtio_rpmsg_bus.c: 336: err = rpmsg_sendto(rpdev->ept, &nsm, sizeof(nsm), RPMSG_NS_ADDR); ... which uses: virtio_rpmsg_sendto() -> rpmsg_send_offchannel_raw() ... which copies its data into an rpmsg_hdr `msg` in virtio_rpmsg_bus.c 618: memcpy(msg->data, data, len); ... and we end up receiving here via a callback: rpmsg_ns.c: 30: /* invoked when a name service announcement arrives */ 31: static int rpmsg_ns_cb(struct rpmsg_device *rpdev, void *data, int len, 32: void *priv, u32 src) 33: { 34: struct rpmsg_ns_msg *msg = data; ... 50: /* don't trust the remote processor for null terminating the name */ 51: msg->name[RPMSG_NAME_SIZE - 1] = '\0'; ... which finally leads into the use of `name` within a format string: rpmsg_ns.c: 57: dev_info(dev, "%sing channel %s addr 0x%x\n", 58: rpmsg32_to_cpu(rpdev, msg->flags) & RPMSG_NS_DESTROY ? 59: "destroy" : "creat", msg->name, chinfo.dst); Taking another look at this comment + NUL-byte assignment: 50: /* don't trust the remote processor for null terminating the name */ 51: msg->name[RPMSG_NAME_SIZE - 1] = '\0'; ... we probably _can_ trust that this string is NUL-terminated with the introduction of strscpy(). However, since there might be some magic happening between the announcement create and the callback that I don't understand, I've opted to leave this comment and assignment alone as it doesn't hurt. We can also observe that `nsm` is not zero-initialized and as such we should maintain the NUL-padding behavior that strncpy() provides: virtio_rpmsg_bus.c: 330: struct rpmsg_ns_msg nsm; Considering the above, a suitable replacement is `strscpy_pad` due to the fact that it guarantees both NUL-termination and NUL-padding on the destination buffer. Now, for the third and final destination buffer rpdev->id.name we can just go for strscpy() (not _pad()) as rpdev points to &vch->rpdev: | rpdev = &vch->rpdev; ... and vch is zero-allocated: | vch = kzalloc(sizeof(*vch), GFP_KERNEL); ... this renders any additional NUL-byte assignments (like the ones strncpy() or strscpy_pad() does) redundant. Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@...r.kernel.org Signed-off-by: Justin Stitt <justinstitt@...gle.com> --- Note: build-tested only. Found with: $ rg "strncpy\(" --- drivers/rpmsg/virtio_rpmsg_bus.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c index 905ac7910c98..dc87965f8164 100644 --- a/drivers/rpmsg/virtio_rpmsg_bus.c +++ b/drivers/rpmsg/virtio_rpmsg_bus.c @@ -329,7 +329,7 @@ static int virtio_rpmsg_announce_create(struct rpmsg_device *rpdev) virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) { struct rpmsg_ns_msg nsm; - strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE); + strscpy_pad(nsm.name, rpdev->id.name, sizeof(nsm.name)); nsm.addr = cpu_to_rpmsg32(rpdev, rpdev->ept->addr); nsm.flags = cpu_to_rpmsg32(rpdev, RPMSG_NS_CREATE); @@ -353,7 +353,7 @@ static int virtio_rpmsg_announce_destroy(struct rpmsg_device *rpdev) virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) { struct rpmsg_ns_msg nsm; - strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE); + strscpy_pad(nsm.name, rpdev->id.name, sizeof(nsm.name)); nsm.addr = cpu_to_rpmsg32(rpdev, rpdev->ept->addr); nsm.flags = cpu_to_rpmsg32(rpdev, RPMSG_NS_DESTROY); @@ -424,7 +424,7 @@ static struct rpmsg_device *__rpmsg_create_channel(struct virtproc_info *vrp, */ rpdev->announce = rpdev->src != RPMSG_ADDR_ANY; - strncpy(rpdev->id.name, chinfo->name, RPMSG_NAME_SIZE); + strscpy(rpdev->id.name, chinfo->name, sizeof(rpdev->id.name)); rpdev->dev.parent = &vrp->vdev->dev; rpdev->dev.release = virtio_rpmsg_release_device; --- base-commit: 9c5d00cb7b6bbc5a7965d9ab7d223b5402d1f02c change-id: 20231020-strncpy-drivers-rpmsg-virtio_rpmsg_bus-c-dba15db4e890 Best regards, -- Justin Stitt <justinstitt@...gle.com>
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