[fips-9] net: tun: fix bugs for oversize packet when napi frags enabled #273
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jira VULN-8828 cve CVE-2023-3812 commit-author Ziyang Xuan <[email protected]> commit 363a532 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: 90e33d4 ("tun: enable napi_gro_frags() for TUN/TAP driver") Signed-off-by: Ziyang Xuan <[email protected]> Reviewed-by: Eric Dumazet <[email protected]> Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Jakub Kicinski <[email protected]> (cherry picked from commit 363a532) Signed-off-by: Brett Mastbergen <[email protected]>
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jira VULN-8828
cve CVE-2023-3812
Build Log
Testing
kselftests were run before and after applying the patch
selftest-5.14.0-284.30.1.el9_2.ciqfips.0.11.1.x86_64.log
selftest-5.14.0-b_f-9-c_5.14.0-284.30.1_VULN-8828-93455db36456+.log