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    Subject[PATCH 4.10 29/62] net: ipv6: RTF_PCPU should not be settable from userspace
    Date
    4.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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
    @@ -1831,6 +1831,10 @@ 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

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