net: gro: properly remove skb from list

Following crash occurs in validate_xmit_skb_list() when same skb is
iterated multiple times in the loop and consume_skb() is called.

The root cause is calling list_del_init(&skb->list) and not clearing
skb->next in d4546c2. list_del_init(&skb->list) sets skb->next
to point to skb itself. skb->next needs to be cleared because other
parts of network stack uses another kind of SKB lists.
validate_xmit_skb_list() uses such list.

A similar type of bugfix was reported by Jesper Dangaard Brouer.
https://patchwork.ozlabs.org/patch/942541/

This patch clears skb->next and changes list_del_init() to list_del()
so that list->prev will maintain the list poison.

[  148.185511] ==================================================================
[  148.187865] BUG: KASAN: use-after-free in validate_xmit_skb_list+0x4b/0xa0
[  148.190158] Read of size 8 at addr ffff8801e52eefc0 by task swapper/1/0
[  148.192940]
[  148.193642] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.18.0-rc3+ #25
[  148.195423] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20180531_142017-buildhw-08.phx2.fedoraproject.org-1.fc28 04/01/2014
[  148.199129] Call Trace:
[  148.200565]  <IRQ>
[  148.201911]  dump_stack+0xc6/0x14c
[  148.203572]  ? dump_stack_print_info.cold.1+0x2f/0x2f
[  148.205083]  ? kmsg_dump_rewind_nolock+0x59/0x59
[  148.206307]  ? validate_xmit_skb+0x2c6/0x560
[  148.207432]  ? debug_show_held_locks+0x30/0x30
[  148.208571]  ? validate_xmit_skb_list+0x4b/0xa0
[  148.211144]  print_address_description+0x6c/0x23c
[  148.212601]  ? validate_xmit_skb_list+0x4b/0xa0
[  148.213782]  kasan_report.cold.6+0x241/0x2fd
[  148.214958]  validate_xmit_skb_list+0x4b/0xa0
[  148.216494]  sch_direct_xmit+0x1b0/0x680
[  148.217601]  ? dev_watchdog+0x4e0/0x4e0
[  148.218675]  ? do_raw_spin_trylock+0x10/0x120
[  148.219818]  ? do_raw_spin_lock+0xe0/0xe0
[  148.221032]  __dev_queue_xmit+0x1167/0x1810
[  148.222155]  ? sched_clock+0x5/0x10
[...]

[  148.474257] Allocated by task 0:
[  148.475363]  kasan_kmalloc+0xbf/0xe0
[  148.476503]  kmem_cache_alloc+0xb4/0x1b0
[  148.477654]  __build_skb+0x91/0x250
[  148.478677]  build_skb+0x67/0x180
[  148.479657]  e1000_clean_rx_irq+0x542/0x8a0
[  148.480757]  e1000_clean+0x652/0xd10
[  148.481772]  net_rx_action+0x4ea/0xc20
[  148.482808]  __do_softirq+0x1f9/0x574
[  148.483831]
[  148.484575] Freed by task 0:
[  148.485504]  __kasan_slab_free+0x12e/0x180
[  148.486589]  kmem_cache_free+0xb4/0x240
[  148.487634]  kfree_skbmem+0xed/0x150
[  148.488648]  consume_skb+0x146/0x250
[  148.489665]  validate_xmit_skb+0x2b7/0x560
[  148.490754]  validate_xmit_skb_list+0x70/0xa0
[  148.491897]  sch_direct_xmit+0x1b0/0x680
[  148.493949]  __dev_queue_xmit+0x1167/0x1810
[  148.495103]  br_dev_queue_push_xmit+0xce/0x250
[  148.496196]  br_forward_finish+0x276/0x280
[  148.497234]  __br_forward+0x44f/0x520
[  148.498260]  br_forward+0x19f/0x1b0
[  148.499264]  br_handle_frame_finish+0x65e/0x980
[  148.500398]  NF_HOOK.constprop.10+0x290/0x2a0
[  148.501522]  br_handle_frame+0x417/0x640
[  148.502582]  __netif_receive_skb_core+0xaac/0x18f0
[  148.503753]  __netif_receive_skb_one_core+0x98/0x120
[  148.504958]  netif_receive_skb_internal+0xe3/0x330
[  148.506154]  napi_gro_complete+0x190/0x2a0
[  148.507243]  dev_gro_receive+0x9f7/0x1100
[  148.508316]  napi_gro_receive+0xcb/0x260
[  148.509387]  e1000_clean_rx_irq+0x2fc/0x8a0
[  148.510501]  e1000_clean+0x652/0xd10
[  148.511523]  net_rx_action+0x4ea/0xc20
[  148.512566]  __do_softirq+0x1f9/0x574
[  148.513598]
[  148.514346] The buggy address belongs to the object at ffff8801e52eefc0
[  148.514346]  which belongs to the cache skbuff_head_cache of size 232
[  148.517047] The buggy address is located 0 bytes inside of
[  148.517047]  232-byte region [ffff8801e52eefc0, ffff8801e52ef0a8)
[  148.519549] The buggy address belongs to the page:
[  148.520726] page:ffffea000794bb00 count:1 mapcount:0 mapping:ffff880106f4dfc0 index:0xffff8801e52ee840 compound_mapcount: 0
[  148.524325] flags: 0x17ffffc0008100(slab|head)
[  148.525481] raw: 0017ffffc0008100 ffff880106b938d0 ffff880106b938d0 ffff880106f4dfc0
[  148.527503] raw: ffff8801e52ee840 0000000000190011 00000001ffffffff 0000000000000000
[  148.529547] page dumped because: kasan: bad access detected

Fixes: d4546c2 ("net: Convert GRO SKB handling to list_head.")
Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Reported-by: Tyler Hicks <tyhicks@canonical.com>
Tested-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5280,7 +5280,8 @@ static void __napi_gro_flush_chain(struct napi_struct *napi, u32 index,
 	list_for_each_entry_safe_reverse(skb, p, head, list) {
 		if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
 			return;
-		list_del_init(&skb->list);
+		list_del(&skb->list);
+		skb->next = NULL;
 		napi_gro_complete(skb);
 		napi->gro_count--;
 		napi->gro_hash[index].count--;
@@ -5461,7 +5462,8 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	ret = NAPI_GRO_CB(skb)->free ? GRO_MERGED_FREE : GRO_MERGED;
 
 	if (pp) {
-		list_del_init(&pp->list);
+		list_del(&pp->list);
+		pp->next = NULL;
 		napi_gro_complete(pp);
 		napi->gro_count--;
 		napi->gro_hash[hash].count--;