From 557c44be917c322860665be3d28376afa84aa936 Mon Sep 17 00:00:00 2001 From: David Ahern Date: Wed, 19 Apr 2017 14:19:43 -0700 Subject: [PATCH] net: ipv6: RTF_PCPU should not be settable from userspace Andrey reported a fault in the IPv6 route code: kasan: GPF could be caused by NULL-ptr deref or user memory access general protection fault: 0000 [#1] SMP KASAN Modules linked in: CPU: 1 PID: 4035 Comm: a.out Not tainted 4.11.0-rc7+ #250 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 task: ffff880069809600 task.stack: ffff880062dc8000 RIP: 0010:ip6_rt_cache_alloc+0xa6/0x560 net/ipv6/route.c:975 RSP: 0018:ffff880062dced30 EFLAGS: 00010206 RAX: dffffc0000000000 RBX: ffff8800670561c0 RCX: 0000000000000006 RDX: 0000000000000003 RSI: ffff880062dcfb28 RDI: 0000000000000018 RBP: ffff880062dced68 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: ffff880062dcfb28 R14: dffffc0000000000 R15: 0000000000000000 FS: 00007feebe37e7c0(0000) GS:ffff88006cb00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000205a0fe4 CR3: 000000006b5c9000 CR4: 00000000000006e0 Call Trace: ip6_pol_route+0x1512/0x1f20 net/ipv6/route.c:1128 ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212 ... Andrey's syzkaller program passes rtmsg.rtmsg_flags with the RTF_PCPU bit set. Flags passed to the kernel are blindly copied to the allocated rt6_info by ip6_route_info_create making a newly inserted route appear as though it is a per-cpu route. ip6_rt_cache_alloc sees the flag set and expects rt->dst.from to be set - which it is not since it is not really a per-cpu copy. The subsequent call to __ip6_dst_alloc then generates the fault. Fix by checking for the flag and failing with EINVAL. Fixes: d52d3997f843f ("ipv6: Create percpu rt6_info") Reported-by: Andrey Konovalov Signed-off-by: David Ahern Acked-by: Martin KaFai Lau Tested-by: Andrey Konovalov Signed-off-by: David S. Miller --- include/uapi/linux/ipv6_route.h | 2 +- net/ipv6/route.c | 4 ++++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h index 85bbb1799df3..d496c02e14bc 100644 --- a/include/uapi/linux/ipv6_route.h +++ b/include/uapi/linux/ipv6_route.h @@ -35,7 +35,7 @@ #define RTF_PREF(pref) ((pref) << 27) #define RTF_PREF_MASK 0x18000000 -#define RTF_PCPU 0x40000000 +#define RTF_PCPU 0x40000000 /* read-only: can not be set by user */ #define RTF_LOCAL 0x80000000 diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 9db1418993f2..fb174b590fd3 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -1854,6 +1854,10 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg) int addr_type; int err = -EINVAL; + /* RTF_PCPU is an internal flag; can not be set by userspace */ + if (cfg->fc_flags & RTF_PCPU) + goto out; + if (cfg->fc_dst_len > 128 || cfg->fc_src_len > 128) goto out; #ifndef CONFIG_IPV6_SUBTREES -- 2.20.1