• Eric Dumazet's avatar
    ipv6/addrconf: fix potential NULL deref in inet6_set_link_af() · db3fa271
    Eric Dumazet authored
    __in6_dev_get(dev) called from inet6_set_link_af() can return NULL.
    
    The needed check has been recently removed, let's add it back.
    
    While do_setlink() does call validate_linkmsg() :
    ...
    err = validate_linkmsg(dev, tb); /* OK at this point */
    ...
    
    It is possible that the following call happening before the
    ->set_link_af() removes IPv6 if MTU is less than 1280 :
    
    if (tb[IFLA_MTU]) {
        err = dev_set_mtu_ext(dev, nla_get_u32(tb[IFLA_MTU]), extack);
        if (err < 0)
              goto errout;
        status |= DO_SETLINK_MODIFIED;
    }
    ...
    
    if (tb[IFLA_AF_SPEC]) {
       ...
       err = af_ops->set_link_af(dev, af);
          ->inet6_set_link_af() // CRASH because idev is NULL
    
    Please note that IPv4 is immune to the bug since inet_set_link_af() does :
    
    struct in_device *in_dev = __in_dev_get_rcu(dev);
    if (!in_dev)
        return -EAFNOSUPPORT;
    
    This problem has been mentioned in commit cf7afbfe ("rtnl: make
    link af-specific updates atomic") changelog :
    
        This method is not fail proof, while it is currently sufficient
        to make set_link_af() inerrable and thus 100% atomic, the
        validation function method will not be able to detect all error
        scenarios in the future, there will likely always be errors
        depending on states which are f.e. not protected by rtnl_mutex
        and thus may change between validation and setting.
    
    IPv6: ADDRCONF(NETDEV_CHANGE): lo: link becomes ready
    general protection fault, probably for non-canonical address 0xdffffc0000000056: 0000 [#1] PREEMPT SMP KASAN
    KASAN: null-ptr-deref in range [0x00000000000002b0-0x00000000000002b7]
    CPU: 0 PID: 9698 Comm: syz-executor712 Not tainted 5.5.0-syzkaller #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    RIP: 0010:inet6_set_link_af+0x66e/0xae0 net/ipv6/addrconf.c:5733
    Code: 38 d0 7f 08 84 c0 0f 85 20 03 00 00 48 8d bb b0 02 00 00 45 0f b6 64 24 04 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 1a 03 00 00 44 89 a3 b0 02 00
    RSP: 0018:ffffc90005b06d40 EFLAGS: 00010206
    RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff86df39a6
    RDX: 0000000000000056 RSI: ffffffff86df3e74 RDI: 00000000000002b0
    RBP: ffffc90005b06e70 R08: ffff8880a2ac0380 R09: ffffc90005b06db0
    R10: fffff52000b60dbe R11: ffffc90005b06df7 R12: 0000000000000000
    R13: 0000000000000000 R14: ffff8880a1fcc424 R15: dffffc0000000000
    FS:  0000000000c46880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 000055f0494ca0d0 CR3: 000000009e4ac000 CR4: 00000000001406f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
     do_setlink+0x2a9f/0x3720 net/core/rtnetlink.c:2754
     rtnl_group_changelink net/core/rtnetlink.c:3103 [inline]
     __rtnl_newlink+0xdd1/0x1790 net/core/rtnetlink.c:3257
     rtnl_newlink+0x69/0xa0 net/core/rtnetlink.c:3377
     rtnetlink_rcv_msg+0x45e/0xaf0 net/core/rtnetlink.c:5438
     netlink_rcv_skb+0x177/0x450 net/netlink/af_netlink.c:2477
     rtnetlink_rcv+0x1d/0x30 net/core/rtnetlink.c:5456
     netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
     netlink_unicast+0x59e/0x7e0 net/netlink/af_netlink.c:1328
     netlink_sendmsg+0x91c/0xea0 net/netlink/af_netlink.c:1917
     sock_sendmsg_nosec net/socket.c:652 [inline]
     sock_sendmsg+0xd7/0x130 net/socket.c:672
     ____sys_sendmsg+0x753/0x880 net/socket.c:2343
     ___sys_sendmsg+0x100/0x170 net/socket.c:2397
     __sys_sendmsg+0x105/0x1d0 net/socket.c:2430
     __do_sys_sendmsg net/socket.c:2439 [inline]
     __se_sys_sendmsg net/socket.c:2437 [inline]
     __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2437
     do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
     entry_SYSCALL_64_after_hwframe+0x49/0xbe
    RIP: 0033:0x4402e9
    Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
    RSP: 002b:00007fffd62fbcf8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
    RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004402e9
    RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000003
    RBP: 00000000006ca018 R08: 0000000000000008 R09: 00000000004002c8
    R10: 0000000000000005 R11: 0000000000000246 R12: 0000000000401b70
    R13: 0000000000401c00 R14: 0000000000000000 R15: 0000000000000000
    Modules linked in:
    ---[ end trace cfa7664b8fdcdff3 ]---
    RIP: 0010:inet6_set_link_af+0x66e/0xae0 net/ipv6/addrconf.c:5733
    Code: 38 d0 7f 08 84 c0 0f 85 20 03 00 00 48 8d bb b0 02 00 00 45 0f b6 64 24 04 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 1a 03 00 00 44 89 a3 b0 02 00
    RSP: 0018:ffffc90005b06d40 EFLAGS: 00010206
    RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff86df39a6
    RDX: 0000000000000056 RSI: ffffffff86df3e74 RDI: 00000000000002b0
    RBP: ffffc90005b06e70 R08: ffff8880a2ac0380 R09: ffffc90005b06db0
    R10: fffff52000b60dbe R11: ffffc90005b06df7 R12: 0000000000000000
    R13: 0000000000000000 R14: ffff8880a1fcc424 R15: dffffc0000000000
    FS:  0000000000c46880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000020000004 CR3: 000000009e4ac000 CR4: 00000000001406e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    
    Fixes: 7dc2bcca ("Validate required parameters in inet6_validate_link_af")
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Bisected-and-reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
    Cc: Maxim Mikityanskiy <maximmi@mellanox.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    db3fa271
addrconf.c 172 KB