| Message ID | 20221029033243.1577015-1-william.xuanziyang@huawei.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net] net: tun: fix bugs for oversize packet when napi frags enabled | expand |
On Fri, Oct 28, 2022 at 8:32 PM Ziyang Xuan <william.xuanziyang@huawei.com> wrote: > > Recently, we got two syzkaller problems because of oversize packet > when napi frags enabled. > > One of the problems is because the first seg size of the iov_iter > from user space is very big, it is 2147479538 which is bigger than > the threshold value for bail out early in __alloc_pages(). And > skb->pfmemalloc is true, __kmalloc_reserve() would use pfmemalloc > reserves without __GFP_NOWARN flag. Thus we got a warning as following: > > ======================================================== > > Restrict the packet size less than ETH_MAX_MTU to fix the problems. > Add len check in tun_napi_alloc_frags() simply. Athough that makes > some kinds of packets payload size slightly smaller than the length > allowed by the protocol, for example, ETH_HLEN + sizeof(struct ipv6hdr) > smaller when the tun device type is IFF_TAP and the packet is IPv6. But > I think that the effect is small and can be ignored. I am not sure about ETH_MAX_MTU being completely safe. napi_get_frags() / napi_alloc_skb() is reserving NET_SKB_PAD + NET_IP_ALIGN bytes. transport_header being an offset from skb->head, we probably want to use (ETH_MAX_MTU - NET_SKB_PAD - NET_IP_ALIGN) My objection to your initial patch was that you were using PAGE_SIZE, while Ethernet MTU can easily be ~9000 But 0xFFFF is a bit too much/risky. Thanks. > > Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") > Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> > --- > drivers/net/tun.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 27c6d235cbda..98d3160fcae2 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1459,7 +1459,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, > int err; > int i; > > - if (it->nr_segs > MAX_SKB_FRAGS + 1) > + if (it->nr_segs > MAX_SKB_FRAGS + 1 || len > ETH_MAX_MTU) > return ERR_PTR(-EMSGSIZE); > > local_bh_disable(); > -- > 2.25.1 >
> On Fri, Oct 28, 2022 at 8:32 PM Ziyang Xuan > <william.xuanziyang@huawei.com> wrote: >> >> Recently, we got two syzkaller problems because of oversize packet >> when napi frags enabled. >> >> One of the problems is because the first seg size of the iov_iter >> from user space is very big, it is 2147479538 which is bigger than >> the threshold value for bail out early in __alloc_pages(). And >> skb->pfmemalloc is true, __kmalloc_reserve() would use pfmemalloc >> reserves without __GFP_NOWARN flag. Thus we got a warning as following: >> >> ======================================================== >> > >> Restrict the packet size less than ETH_MAX_MTU to fix the problems. >> Add len check in tun_napi_alloc_frags() simply. Athough that makes >> some kinds of packets payload size slightly smaller than the length >> allowed by the protocol, for example, ETH_HLEN + sizeof(struct ipv6hdr) >> smaller when the tun device type is IFF_TAP and the packet is IPv6. But >> I think that the effect is small and can be ignored. > > I am not sure about ETH_MAX_MTU being completely safe. > > napi_get_frags() / napi_alloc_skb() is reserving NET_SKB_PAD + > NET_IP_ALIGN bytes. > > transport_header being an offset from skb->head, > we probably want to use (ETH_MAX_MTU - NET_SKB_PAD - NET_IP_ALIGN) Hi Eric, Thank you for your review. I did not notice the reserved skb space. I will fix it in v2 patch. Thanks. > > My objection to your initial patch was that you were using PAGE_SIZE, > while Ethernet MTU can easily be ~9000 > > But 0xFFFF is a bit too much/risky. > > Thanks. > >> >> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") >> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> >> --- >> drivers/net/tun.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c >> index 27c6d235cbda..98d3160fcae2 100644 >> --- a/drivers/net/tun.c >> +++ b/drivers/net/tun.c >> @@ -1459,7 +1459,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, >> int err; >> int i; >> >> - if (it->nr_segs > MAX_SKB_FRAGS + 1) >> + if (it->nr_segs > MAX_SKB_FRAGS + 1 || len > ETH_MAX_MTU) >> return ERR_PTR(-EMSGSIZE); >> >> local_bh_disable(); >> -- >> 2.25.1 >> > . >
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 27c6d235cbda..98d3160fcae2 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1459,7 +1459,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, int err; int i; - if (it->nr_segs > MAX_SKB_FRAGS + 1) + if (it->nr_segs > MAX_SKB_FRAGS + 1 || len > ETH_MAX_MTU) return ERR_PTR(-EMSGSIZE); local_bh_disable();
Recently, we got two syzkaller problems because of oversize packet when napi frags enabled. One of the problems is because the first seg size of the iov_iter from user space is very big, it is 2147479538 which is bigger than the threshold value for bail out early in __alloc_pages(). And skb->pfmemalloc is true, __kmalloc_reserve() would use pfmemalloc reserves without __GFP_NOWARN flag. Thus we got a warning as following: ======================================================== WARNING: CPU: 1 PID: 17965 at mm/page_alloc.c:5295 __alloc_pages+0x1308/0x16c4 mm/page_alloc.c:5295 ... Call trace: __alloc_pages+0x1308/0x16c4 mm/page_alloc.c:5295 __alloc_pages_node include/linux/gfp.h:550 [inline] alloc_pages_node include/linux/gfp.h:564 [inline] kmalloc_large_node+0x94/0x350 mm/slub.c:4038 __kmalloc_node_track_caller+0x620/0x8e4 mm/slub.c:4545 __kmalloc_reserve.constprop.0+0x1e4/0x2b0 net/core/skbuff.c:151 pskb_expand_head+0x130/0x8b0 net/core/skbuff.c:1654 __skb_grow include/linux/skbuff.h:2779 [inline] tun_napi_alloc_frags+0x144/0x610 drivers/net/tun.c:1477 tun_get_user+0x31c/0x2010 drivers/net/tun.c:1835 tun_chr_write_iter+0x98/0x100 drivers/net/tun.c:2036 The other problem is because odd IPv6 packets without NEXTHDR_NONE extension header and have big packet length, it is 2127925 which is bigger than ETH_MAX_MTU(65535). After ipv6_gso_pull_exthdrs() in ipv6_gro_receive(), network_header offset and transport_header offset are all bigger than U16_MAX. That would trigger skb->network_header and skb->transport_header overflow error, because they are all '__u16' type. Eventually, it would affect the value for __skb_push(skb, value), and make it be a big value. After __skb_push() in ipv6_gro_receive(), skb->data would less than skb->head, an out of bounds memory bug occurred. That would trigger the problem as following: ================================================================== BUG: KASAN: use-after-free in eth_type_trans+0x100/0x260 ... Call trace: dump_backtrace+0xd8/0x130 show_stack+0x1c/0x50 dump_stack_lvl+0x64/0x7c print_address_description.constprop.0+0xbc/0x2e8 print_report+0x100/0x1e4 kasan_report+0x80/0x120 __asan_load8+0x78/0xa0 eth_type_trans+0x100/0x260 napi_gro_frags+0x164/0x550 tun_get_user+0xda4/0x1270 tun_chr_write_iter+0x74/0x130 do_iter_readv_writev+0x130/0x1ec do_iter_write+0xbc/0x1e0 vfs_writev+0x13c/0x26c Restrict the packet size less than ETH_MAX_MTU to fix the problems. Add len check in tun_napi_alloc_frags() simply. Athough that makes some kinds of packets payload size slightly smaller than the length allowed by the protocol, for example, ETH_HLEN + sizeof(struct ipv6hdr) smaller when the tun device type is IFF_TAP and the packet is IPv6. But I think that the effect is small and can be ignored. Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver") Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> --- drivers/net/tun.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)