| From foo@baz Sat Apr 29 08:22:13 CEST 2017 |
| From: David Ahern <dsa@cumulusnetworks.com> |
| Date: Wed, 19 Apr 2017 14:19:43 -0700 |
| Subject: net: ipv6: RTF_PCPU should not be settable from userspace |
| |
| From: David Ahern <dsa@cumulusnetworks.com> |
| |
| |
| [ Upstream commit 557c44be917c322860665be3d28376afa84aa936 ] |
| |
| 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 <andreyknvl@google.com> |
| Signed-off-by: David Ahern <dsa@cumulusnetworks.com> |
| Acked-by: Martin KaFai Lau <kafai@fb.com> |
| Tested-by: Andrey Konovalov <andreyknvl@google.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| include/uapi/linux/ipv6_route.h | 2 +- |
| net/ipv6/route.c | 4 ++++ |
| 2 files changed, 5 insertions(+), 1 deletion(-) |
| |
| --- a/include/uapi/linux/ipv6_route.h |
| +++ b/include/uapi/linux/ipv6_route.h |
| @@ -34,7 +34,7 @@ |
| #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 |
| |
| |
| --- a/net/ipv6/route.c |
| +++ b/net/ipv6/route.c |
| @@ -1826,6 +1826,10 @@ static struct rt6_info *ip6_route_info_c |
| 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 |