From: Tadeusz Struk tadeusz.struk@linaro.org
commit 5e34af4142ffe68f01c8a9acae83300f8911e20c upstream.
Syzbot found a kernel bug in the ipv6 stack: LINK: https://syzkaller.appspot.com/bug?id=205d6f11d72329ab8d62a610c44c5e7e2541558... The reproducer triggers it by sending a crafted message via sendmmsg() call, which triggers skb_over_panic, and crashes the kernel:
skbuff: skb_over_panic: text:ffffffff84647fb4 len:65575 put:65575 head:ffff888109ff0000 data:ffff888109ff0088 tail:0x100af end:0xfec0 dev:<NULL>
Update the check that prevents an invalid packet with MTU equal to the fregment header size to eat up all the space for payload.
The reproducer can be found here: LINK: https://syzkaller.appspot.com/text?tag=ReproC&x=1648c83fb00000
Reported-by: syzbot+e223cf47ec8ae183f2a0@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org Acked-by: Willem de Bruijn willemb@google.com Link: https://lore.kernel.org/r/20220310232538.1044947-1-tadeusz.struk@linaro.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/ip6_output.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1500,8 +1500,8 @@ static int __ip6_append_data(struct sock sizeof(struct frag_hdr) : 0) + rt->rt6i_nfheader_len;
- if (mtu < fragheaderlen || - ((mtu - fragheaderlen) & ~7) + fragheaderlen < sizeof(struct frag_hdr)) + if (mtu <= fragheaderlen || + ((mtu - fragheaderlen) & ~7) + fragheaderlen <= sizeof(struct frag_hdr)) goto emsgsize;
maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen -