| Message ID | 1569829469-16143-1-git-send-email-dongli.zhang@oracle.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/1] xen-netfront: do not use ~0U as error return value for xennet_fill_frags() | expand |
On 30.09.19 09:44, Dongli Zhang wrote: > xennet_fill_frags() uses ~0U as return value when the sk_buff is not able > to cache extra fragments. This is incorrect because the return type of > xennet_fill_frags() is RING_IDX and 0xffffffff is an expected value for > ring buffer index. > > In the situation when the rsp_cons is approaching 0xffffffff, the return > value of xennet_fill_frags() may become 0xffffffff which xennet_poll() (the > caller) would regard as error. As a result, queue->rx.rsp_cons is set > incorrectly because it is updated only when there is error. If there is no > error, xennet_poll() would be responsible to update queue->rx.rsp_cons. > Finally, queue->rx.rsp_cons would point to the rx ring buffer entries whose > queue->rx_skbs[i] and queue->grant_rx_ref[i] are already cleared to NULL. > This leads to NULL pointer access in the next iteration to process rx ring > buffer entries. > > The symptom is similar to the one fixed in > commit 00b368502d18 ("xen-netfront: do not assume sk_buff_head list is > empty in error handling"). > > This patch uses an extra argument to help return if there is error in > xennet_fill_frags(). Hmm, I wonder if it wouldn't be better to have the ring index returned via the new pointer and let return xennet_fill_frags() 0 in case of success and -ENOENT otherwise. This would avoid having to introduce the local errno variable. Juergen > > Fixes: ad4f15dc2c70 ("xen/netfront: don't bug in case of too many frags") > Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com> > --- > drivers/net/xen-netfront.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c > index e14ec75..c2a1e09 100644 > --- a/drivers/net/xen-netfront.c > +++ b/drivers/net/xen-netfront.c > @@ -889,11 +889,14 @@ static int xennet_set_skb_gso(struct sk_buff *skb, > > static RING_IDX xennet_fill_frags(struct netfront_queue *queue, > struct sk_buff *skb, > - struct sk_buff_head *list) > + struct sk_buff_head *list, > + int *errno) > { > RING_IDX cons = queue->rx.rsp_cons; > struct sk_buff *nskb; > > + *errno = 0; > + > while ((nskb = __skb_dequeue(list))) { > struct xen_netif_rx_response *rx = > RING_GET_RESPONSE(&queue->rx, ++cons); > @@ -908,6 +911,7 @@ static RING_IDX xennet_fill_frags(struct netfront_queue *queue, > if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) { > queue->rx.rsp_cons = ++cons + skb_queue_len(list); > kfree_skb(nskb); > + *errno = -ENOENT; > return ~0U; > } > > @@ -1009,6 +1013,8 @@ static int xennet_poll(struct napi_struct *napi, int budget) > i = queue->rx.rsp_cons; > work_done = 0; > while ((i != rp) && (work_done < budget)) { > + int errno; > + > memcpy(rx, RING_GET_RESPONSE(&queue->rx, i), sizeof(*rx)); > memset(extras, 0, sizeof(rinfo.extras)); > > @@ -1045,8 +1051,8 @@ static int xennet_poll(struct napi_struct *napi, int budget) > skb->data_len = rx->status; > skb->len += rx->status; > > - i = xennet_fill_frags(queue, skb, &tmpq); > - if (unlikely(i == ~0U)) > + i = xennet_fill_frags(queue, skb, &tmpq, &errno); > + if (unlikely(errno == -ENOENT)) > goto err; > > if (rx->flags & XEN_NETRXF_csum_blank) >
diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c index e14ec75..c2a1e09 100644 --- a/drivers/net/xen-netfront.c +++ b/drivers/net/xen-netfront.c @@ -889,11 +889,14 @@ static int xennet_set_skb_gso(struct sk_buff *skb, static RING_IDX xennet_fill_frags(struct netfront_queue *queue, struct sk_buff *skb, - struct sk_buff_head *list) + struct sk_buff_head *list, + int *errno) { RING_IDX cons = queue->rx.rsp_cons; struct sk_buff *nskb; + *errno = 0; + while ((nskb = __skb_dequeue(list))) { struct xen_netif_rx_response *rx = RING_GET_RESPONSE(&queue->rx, ++cons); @@ -908,6 +911,7 @@ static RING_IDX xennet_fill_frags(struct netfront_queue *queue, if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) { queue->rx.rsp_cons = ++cons + skb_queue_len(list); kfree_skb(nskb); + *errno = -ENOENT; return ~0U; } @@ -1009,6 +1013,8 @@ static int xennet_poll(struct napi_struct *napi, int budget) i = queue->rx.rsp_cons; work_done = 0; while ((i != rp) && (work_done < budget)) { + int errno; + memcpy(rx, RING_GET_RESPONSE(&queue->rx, i), sizeof(*rx)); memset(extras, 0, sizeof(rinfo.extras)); @@ -1045,8 +1051,8 @@ static int xennet_poll(struct napi_struct *napi, int budget) skb->data_len = rx->status; skb->len += rx->status; - i = xennet_fill_frags(queue, skb, &tmpq); - if (unlikely(i == ~0U)) + i = xennet_fill_frags(queue, skb, &tmpq, &errno); + if (unlikely(errno == -ENOENT)) goto err; if (rx->flags & XEN_NETRXF_csum_blank)
xennet_fill_frags() uses ~0U as return value when the sk_buff is not able to cache extra fragments. This is incorrect because the return type of xennet_fill_frags() is RING_IDX and 0xffffffff is an expected value for ring buffer index. In the situation when the rsp_cons is approaching 0xffffffff, the return value of xennet_fill_frags() may become 0xffffffff which xennet_poll() (the caller) would regard as error. As a result, queue->rx.rsp_cons is set incorrectly because it is updated only when there is error. If there is no error, xennet_poll() would be responsible to update queue->rx.rsp_cons. Finally, queue->rx.rsp_cons would point to the rx ring buffer entries whose queue->rx_skbs[i] and queue->grant_rx_ref[i] are already cleared to NULL. This leads to NULL pointer access in the next iteration to process rx ring buffer entries. The symptom is similar to the one fixed in commit 00b368502d18 ("xen-netfront: do not assume sk_buff_head list is empty in error handling"). This patch uses an extra argument to help return if there is error in xennet_fill_frags(). Fixes: ad4f15dc2c70 ("xen/netfront: don't bug in case of too many frags") Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com> --- drivers/net/xen-netfront.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)