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
To fix the problems, restrict the packet size less than
(ETH_MAX_MTU - NET_SKB_PAD - NET_IP_ALIGN) which has considered reserved
skb space in napi_alloc_skb() because transport_header is an offset from
skb->head. Add len check in tun_napi_alloc_frags() simply.
Fixes: 90e33d4594 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20221029094101.1653855-1-william.xuanziyang@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
363a5328f4