There seems to be a heap-buffer-overflow in parse_vlanid

[evverx]

The networkd fuzzer I mentioned in #10628 keeps finding issues in networkd (though, it can't even get past the initial corpus). The following netdev config causes a heap-buffer-overflow in parse_vlanid:

[NetDev]
Name=vlan99
Kind=vcan

[VLAN]
Id=99
GVRP=true
MVRP=true
LooseBinding=true
ReorderHeader=true

==2748==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60b000000210 at pc 0x7fbc716ec9cd bp 0x7ffd6f992f50 sp 0x7ffd6f992f40
WRITE of size 2 at 0x60b000000210 thread T0
    #0 0x7fbc716ec9cc in parse_vlanid ../src/shared/vlan-util.c:18
    #1 0x7fbc716ecce0 in config_parse_vlanid ../src/shared/vlan-util.c:68
    #2 0x7fbc71631acc in next_assignment ../src/shared/conf-parser.c:138
    #3 0x7fbc71632e77 in parse_line ../src/shared/conf-parser.c:263
    #4 0x7fbc71633d89 in config_parse ../src/shared/conf-parser.c:380
    #5 0x5612b024b57b in netdev_load_one ../src/network/netdev/netdev.c:662
    #6 0x5612b023d7b2 in LLVMFuzzerTestOneInput ../src/network/fuzz-networkd.c:30
    #7 0x5612b023dca8 in main ../src/fuzz/fuzz-main.c:33
    #8 0x7fbc6fc3511a in __libc_start_main (/lib64/libc.so.6+0x2311a)
    #9 0x5612b023d279 in _start (/home/vagrant/systemd/build/fuzz-networkd+0x24d279)

0x60b000000210 is located 0 bytes to the right of 112-byte region [0x60b0000001a0,0x60b000000210)
allocated by thread T0 here:
    #0 0x7fbc7280ae50 in calloc (/lib64/libasan.so.5+0xeee50)
    #1 0x5612b024aa0b in netdev_load_one ../src/network/netdev/netdev.c:650
    #2 0x5612b023d7b2 in LLVMFuzzerTestOneInput ../src/network/fuzz-networkd.c:30
    #3 0x5612b023dca8 in main ../src/fuzz/fuzz-main.c:33
    #4 0x7fbc6fc3511a in __libc_start_main (/lib64/libc.so.6+0x2311a)

SUMMARY: AddressSanitizer: heap-buffer-overflow ../src/shared/vlan-util.c:18 in parse_vlanid
Shadow bytes around the buggy address:
  0x0c167fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c167fff8000: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c167fff8010: 00 00 00 00 00 fa fa fa fa fa fa fa fa fa 00 00
  0x0c167fff8020: 00 00 00 00 00 00 00 00 00 00 00 00 fa fa fa fa
  0x0c167fff8030: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c167fff8040: 00 00[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c167fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c167fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c167fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c167fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c167fff8090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
==2748==ABORTING

By the way, does anybody know what's up with the wireguard code? The example from the documentation crashes the fuzzer with something like:

wg0: loaded wireguard
wg0: Creating
Assertion '!w->unresolved_endpoints' failed at ../src/network/netdev/wireguard.c:679, function wireguard_done(). Aborting.

Here's how networkd reacts to the same config:

Started Network Service.
wg0: netdev could not be created: Operation not supported
Stopping Network Service...
Assertion '!w->unresolved_endpoints' failed at ../src/network/netdev/wireguard.c:679, function wireguard_done(). Aborting.
systemd-networkd.service: Main process exited, code=killed, status=6/ABRT
systemd-networkd.service: Failed with result 'signal'.

@Mic92 do you know what that could be?

[Mic92]

The solution provided @yuwata should fix this particular assertion.