CVE-2024-35888

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

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

syzbot reported a problem in ip6erspan_rcv() [1]

Issue is that ip6erspanrcv() (and erspanrcv()) no longer make sure erspanbasehdr is present in skb linear part (skb->head) before getting @ver field from it.

Add the missing pskbmaypull() calls.

v2: Reload iph pointer in erspanrcv() after pskbmay_pull() because skb->head might have changed.

[1]

BUG: KMSAN: uninit-value in pskbmaypullreason include/linux/skbuff.h:2742 [inline] BUG: KMSAN: uninit-value in pskbmaypull include/linux/skbuff.h:2756 [inline] BUG: KMSAN: uninit-value in ip6erspanrcv net/ipv6/ip6gre.c:541 [inline] BUG: KMSAN: uninit-value in grercv+0x11f8/0x1930 net/ipv6/ip6gre.c:610 pskbmaypullreason include/linux/skbuff.h:2742 [inline] pskbmaypull include/linux/skbuff.h:2756 [inline] ip6erspanrcv net/ipv6/ip6gre.c:541 [inline] grercv+0x11f8/0x1930 net/ipv6/ip6gre.c:610 ip6protocoldeliverrcu+0x1d4c/0x2ca0 net/ipv6/ip6input.c:438 ip6inputfinish net/ipv6/ip6input.c:483 [inline] NFHOOK include/linux/netfilter.h:314 [inline] ip6input+0x15d/0x430 net/ipv6/ip6input.c:492 ip6mcinput+0xa7e/0xc80 net/ipv6/ip6input.c:586 dstinput include/net/dst.h:460 [inline] ip6rcvfinish+0x955/0x970 net/ipv6/ip6input.c:79 NFHOOK include/linux/netfilter.h:314 [inline] ipv6rcv+0xde/0x390 net/ipv6/ip6input.c:310 __netifreceiveskbonecore net/core/dev.c:5538 [inline] __netifreceiveskb+0x1da/0xa00 net/core/dev.c:5652 netifreceiveskbinternal net/core/dev.c:5738 [inline] netifreceiveskb+0x58/0x660 net/core/dev.c:5798 tunrxbatched+0x3ee/0x980 drivers/net/tun.c:1549 tungetuser+0x5566/0x69e0 drivers/net/tun.c:2002 tunchrwriteiter+0x3af/0x5d0 drivers/net/tun.c:2048 callwriteiter include/linux/fs.h:2108 [inline] newsyncwrite fs/readwrite.c:497 [inline] vfswrite+0xb63/0x1520 fs/readwrite.c:590 ksyswrite+0x20f/0x4c0 fs/read_write.c:643 __dosyswrite fs/read_write.c:655 [inline] __sesyswrite fs/read_write.c:652 [inline] _x64syswrite+0x93/0xe0 fs/readwrite.c:652 dosyscall64+0xd5/0x1f0 entrySYSCALL64afterhwframe+0x6d/0x75

Uninit was created at: slabpostallochook mm/slub.c:3804 [inline] slaballocnode mm/slub.c:3845 [inline] kmemcacheallocnode+0x613/0xc50 mm/slub.c:3888 kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577 __allocskb+0x35b/0x7a0 net/core/skbuff.c:668 allocskb include/linux/skbuff.h:1318 [inline] allocskbwithfrags+0xc8/0xbf0 net/core/skbuff.c:6504 sockallocsendpskb+0xa81/0xbf0 net/core/sock.c:2795 tunallocskb drivers/net/tun.c:1525 [inline] tungetuser+0x209a/0x69e0 drivers/net/tun.c:1846 tunchrwriteiter+0x3af/0x5d0 drivers/net/tun.c:2048 callwriteiter include/linux/fs.h:2108 [inline] newsyncwrite fs/readwrite.c:497 [inline] vfswrite+0xb63/0x1520 fs/readwrite.c:590 ksyswrite+0x20f/0x4c0 fs/readwrite.c:643 __dosyswrite fs/read_write.c:655 [inline] __sesyswrite fs/read_write.c:652 [inline] _x64syswrite+0x93/0xe0 fs/readwrite.c:652 dosyscall64+0xd5/0x1f0 entrySYSCALL64afterhwframe+0x6d/0x75

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