CVE-2024-35888

In the Linux kernel, the following vulnerability has been resolved:

erspan: make sure erspan_base_hdr is present in skb->head

syzbot reported a problem in ip6erspan_rcv() [1]

Issue is that ip6erspan_rcv() (and erspan_rcv()) no longer make

sure erspan_base_hdr is present in skb linear part (skb->head)

before getting @ver field from it.

Add the missing pskb_may_pull() calls.

v2: Reload iph pointer in erspan_rcv() after pskb_may_pull()

because skb->head might have changed.

[1]

BUG: KMSAN: uninit-value in pskb_may_pull_reason include/linux/skbuff.h:2742 [inline]

BUG: KMSAN: uninit-value in pskb_may_pull include/linux/skbuff.h:2756 [inline]

BUG: KMSAN: uninit-value in ip6erspan_rcv net/ipv6/ip6_gre.c:541 [inline]

BUG: KMSAN: uninit-value in gre_rcv+0x11f8/0x1930 net/ipv6/ip6_gre.c:610

pskb_may_pull_reason include/linux/skbuff.h:2742 [inline]

pskb_may_pull include/linux/skbuff.h:2756 [inline]

ip6erspan_rcv net/ipv6/ip6_gre.c:541 [inline]

gre_rcv+0x11f8/0x1930 net/ipv6/ip6_gre.c:610

ip6_protocol_deliver_rcu+0x1d4c/0x2ca0 net/ipv6/ip6_input.c:438

ip6_input_finish net/ipv6/ip6_input.c:483 [inline]

NF_HOOK include/linux/netfilter.h:314 [inline]

ip6_input+0x15d/0x430 net/ipv6/ip6_input.c:492

ip6_mc_input+0xa7e/0xc80 net/ipv6/ip6_input.c:586

dst_input include/net/dst.h:460 [inline]

ip6_rcv_finish+0x955/0x970 net/ipv6/ip6_input.c:79

NF_HOOK include/linux/netfilter.h:314 [inline]

ipv6_rcv+0xde/0x390 net/ipv6/ip6_input.c:310

__netif_receive_skb_one_core net/core/dev.c:5538 [inline]

__netif_receive_skb+0x1da/0xa00 net/core/dev.c:5652

netif_receive_skb_internal net/core/dev.c:5738 [inline]

netif_receive_skb+0x58/0x660 net/core/dev.c:5798

tun_rx_batched+0x3ee/0x980 drivers/net/tun.c:1549

tun_get_user+0x5566/0x69e0 drivers/net/tun.c:2002

tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048

call_write_iter include/linux/fs.h:2108 [inline]

new_sync_write fs/read_write.c:497 [inline]

vfs_write+0xb63/0x1520 fs/read_write.c:590

ksys_write+0x20f/0x4c0 fs/read_write.c:643

__do_sys_write fs/read_write.c:655 [inline]

__se_sys_write fs/read_write.c:652 [inline]

__x64_sys_write+0x93/0xe0 fs/read_write.c:652

do_syscall_64+0xd5/0x1f0

entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was created at:

slab_post_alloc_hook mm/slub.c:3804 [inline]

slab_alloc_node mm/slub.c:3845 [inline]

kmem_cache_alloc_node+0x613/0xc50 mm/slub.c:3888

kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577

__alloc_skb+0x35b/0x7a0 net/core/skbuff.c:668

alloc_skb include/linux/skbuff.h:1318 [inline]

alloc_skb_with_frags+0xc8/0xbf0 net/core/skbuff.c:6504

sock_alloc_send_pskb+0xa81/0xbf0 net/core/sock.c:2795

tun_alloc_skb drivers/net/tun.c:1525 [inline]

tun_get_user+0x209a/0x69e0 drivers/net/tun.c:1846

tun_chr_write_iter+0x3af/0x5d0 drivers/net/tun.c:2048

call_write_iter include/linux/fs.h:2108 [inline]

new_sync_write fs/read_write.c:497 [inline]

vfs_write+0xb63/0x1520 fs/read_write.c:590

ksys_write+0x20f/0x4c0 fs/read_write.c:643

__do_sys_write fs/read_write.c:655 [inline]

__se_sys_write fs/read_write.c:652 [inline]

__x64_sys_write+0x93/0xe0 fs/read_write.c:652

do_syscall_64+0xd5/0x1f0

entry_SYSCALL_64_after_hwframe+0x6d/0x75

CPU: 1 PID: 5045 Comm: syz-executor114 Not tainted 6.9.0-rc1-syzkaller-00021-g962490525cff #0