Xcode Address Sanitizer issue with sockaddr

问题

The following code is used to convert a sockaddr to a sockaddr_in6 to get the IPv6 address:

extension sockaddr {
  private var addressV6: String {
    var me = self
    var buffer = [Int8](repeating: 0, count: Int(INET6_ADDRSTRLEN))

    withUnsafePointer(to: &me) {
      $0.withMemoryRebound(to: sockaddr_in6.self, capacity: 1) {
        var addrV6 = $0.pointee.sin6_addr
        inet_ntop(AF_INET6, &addrV6, &buffer, socklen_t(INET6_ADDRSTRLEN))
      }
    }

    return String(cString: buffer)
  }
}

When I run the code in Xcode 9 beta with the Address Sanitizer, execution stops on this line:

var addrV6 = $0.pointee.sin6_addr

With the following message (plus a lot of memory info):

AddressSanitizer: stack-buffer-overflow on address 0x000131810077 at pc 0x00010a3c06d5 bp 0x7fff55ded010 sp 0x7fff55ded008 READ of size 16 at 0x000131810077 thread T0

I can understand that the ASAN is concerned that I'm reading past the boundaries of the sockaddr to get the full sockaddr_in6 (the sockaddr is 16 bytes, the sockaddr_in6 is 28 bytes).

But I can't seem to test the rest of my app with the ASAN because of this. It seems a bit weird that any use of withMemoryRebound would trip the ASAN.

I've tried to write it in different ways, even using Data as a vessle for the bytes. But I always seem to end up with a solution that triggers the ASAN.

Is there something wrong with my code?
Or can I somehow ignore this function in the ASAN?

回答1:

The pointer returned by the getifaddrs function looks like a sockaddr pointer but is actually a pointer to sockaddr_in or sockaddr_in6. By moving the addressV6 function to an extension on sockaddr, the memory was copied and cut to the size of a sockaddr struct. In case of IPv6 valuable address information would get lost.

The new (trimmed) sockaddr could never be converted to a sockaddr_in6 triggering the SAN.

For more information see: Swift getnameinfo unreliable results for IPv6

Thank you @MartinR for helping me with this!

来源：https://stackoverflow.com/questions/44426911/xcode-address-sanitizer-issue-with-sockaddr

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swift

xcode

pointers

address-sanitizer