UAF in client_close

[meme]

Looks like due to improper bookkeeping client_close is called twice for the same client, which has already been free'd, leading to a UAF.

ASan:

==33430==ERROR: AddressSanitizer: heap-use-after-free on address 0x6080000007a0
at pc 0x55d4554839b3 bp 0x7ffe3219c350 sp 0x7ffe3219c340
READ of size 4 at 0x6080000007a0 thread T0
    #0 0x55d4554839b2 in client_close /usbfluxd/usbfluxd/client.c:238
    #1 0x55d455485059 in client_notify_remote_close /usbfluxd/usbfluxd/client.c:390
    #2 0x55d4554922d8 in usbmux_remote_dispose /usbfluxd/usbfluxd/usbmux_remote.c:914
    #3 0x55d45549113a in remote_mark_dead /usbfluxd/usbfluxd/usbmux_remote.c:552
    #4 0x55d45549253d in usbmux_remote_mark_dead /usbfluxd/usbfluxd/usbmux_remote.c:933
    #5 0x55d4554956c2 in remote_process_recv /usbfluxd/usbfluxd/usbmux_remote.c:1231
    #6 0x55d4554967b6 in usbmux_remote_process /usbfluxd/usbfluxd/usbmux_remote.c:1343
    #7 0x55d455499526 in main_loop /usbfluxd/usbfluxd/main.c:159
    #8 0x55d45549a870 in main /usbfluxd/usbfluxd/main.c:477
    #9 0x7f3ed253bb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
    #10 0x55d45548295d in _start (/usr/local/sbin/usbfluxd+0xa95d)
0x6080000007a0 is located 0 bytes inside of 96-byte region [0x6080000007a0,0x608
000000800)
freed by thread T0 here:
    #0 0x7f3ed2932f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
    #1 0x55d455483c29 in client_close /usbfluxd/usbfluxd/client.c:254
    #2 0x55d45548b19d in client_process /usbfluxd/usbfluxd/client.c:1019
    #3 0x55d4554993cf in main_loop /usbfluxd/usbfluxd/main.c:156
    #4 0x55d45549a870 in main /usbfluxd/usbfluxd/main.c:477
    #5 0x7f3ed253bb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
previously allocated by thread T0 here:
    #0 0x7f3ed2933279 in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x55d45548334c in client_accept /usbfluxd/usbfluxd/client.c:199
    #2 0x55d455499242 in main_loop /usbfluxd/usbfluxd/main.c:149
    #3 0x55d45549a870 in main /usbfluxd/usbfluxd/main.c:477
    #4 0x7f3ed253bb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
SUMMARY: AddressSanitizer: heap-use-after-free /usbfluxd/usbfluxd/client.c:238 in client_close
Shadow bytes around the buggy address:
  0x0c107fff80a0: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff80b0: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff80c0: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff80d0: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff80e0: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c107fff80f0: fa fa fa fa[fd]fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff8100: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff8110: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff8120: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff8130: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c107fff8140: fa fa fa fa fd fd fd fd fd fd fd fd fd fd fd fd
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==33430==ABORTING

[sbingner]

This should now be fixed in master - if you can verify