Re: [PATCH v6 6/7] net/eth: Read ip6_ext_hdr_routing buffer before accessing it

[Philippe Mathieu-Daudé]

On 3/17/21 5:35 PM, Alexander Bulekov wrote:
> Correction: there was a response suggesting to add padding to ip6_ext_hdr.

Was the response on the public list or the private security one?

If it was public I missed it. On a private list such comment isn't
very helpful if nobody sends patches to fix it. Maybe we need to
review the security list process.

> On 210317 1233, Alexander Bulekov wrote:
>> Just noticed that I also reported this to QEMU-Security on 2020-05-17.
>> The problem was acknowledged, but I don't think there was any
>> communication after that, so I'm not sure whether this is also stuck in
>> some private issue tracker. Seems pretty tame as far as
>> memory-corrputions go, but I'll send a followup to the private report,
>> to see if it went anywhere..
>> -Alex
>>
>> On 210310 1931, Philippe Mathieu-Daudé wrote:
>>> We can't know the caller read enough data in the memory pointed
>>> by ext_hdr to cast it as a ip6_ext_hdr_routing.
>>> Declare rt_hdr on the stack and fill it again from the iovec.
>>>
>>> Since we already checked there is enough data in the iovec buffer,
>>> simply add an assert() call to consume the bytes_read variable.
>>>
>>> This fix a 2 bytes buffer overrun in eth_parse_ipv6_hdr() reported
>>> by QEMU fuzzer:
>>>
>>>   $ cat << EOF | ./qemu-system-i386 -M pc-q35-5.0 \
>>>     -accel qtest -monitor none \
>>>     -serial none -nographic -qtest stdio
>>>   outl 0xcf8 0x80001010
>>>   outl 0xcfc 0xe1020000
>>>   outl 0xcf8 0x80001004
>>>   outw 0xcfc 0x7
>>>   write 0x25 0x1 0x86
>>>   write 0x26 0x1 0xdd
>>>   write 0x4f 0x1 0x2b
>>>   write 0xe1020030 0x4 0x190002e1
>>>   write 0xe102003a 0x2 0x0807
>>>   write 0xe1020048 0x4 0x12077cdd
>>>   write 0xe1020400 0x4 0xba077cdd
>>>   write 0xe1020420 0x4 0x190002e1
>>>   write 0xe1020428 0x4 0x3509d807
>>>   write 0xe1020438 0x1 0xe2
>>>   EOF
>>>   =================================================================
>>>   ==2859770==ERROR: AddressSanitizer: stack-buffer-overflow on address 
>>> 0x7ffdef904902 at pc 0x561ceefa78de bp 0x7ffdef904820 sp 0x7ffdef904818
>>>   READ of size 1 at 0x7ffdef904902 thread T0
>>>       #0 0x561ceefa78dd in _eth_get_rss_ex_dst_addr net/eth.c:410:17
>>>       #1 0x561ceefa41fb in eth_parse_ipv6_hdr net/eth.c:532:17
>>>       #2 0x561cef7de639 in net_tx_pkt_parse_headers 
>>> hw/net/net_tx_pkt.c:228:14
>>>       #3 0x561cef7dbef4 in net_tx_pkt_parse hw/net/net_tx_pkt.c:273:9
>>>       #4 0x561ceec29f22 in e1000e_process_tx_desc 
>>> hw/net/e1000e_core.c:730:29
>>>       #5 0x561ceec28eac in e1000e_start_xmit hw/net/e1000e_core.c:927:9
>>>       #6 0x561ceec1baab in e1000e_set_tdt hw/net/e1000e_core.c:2444:9
>>>       #7 0x561ceebf300e in e1000e_core_write hw/net/e1000e_core.c:3256:9
>>>       #8 0x561cef3cd4cd in e1000e_mmio_write hw/net/e1000e.c:110:5
>>>
>>>   Address 0x7ffdef904902 is located in stack of thread T0 at offset 34 in 
>>> frame
>>>       #0 0x561ceefa320f in eth_parse_ipv6_hdr net/eth.c:486
>>>
>>>     This frame has 1 object(s):
>>>       [32, 34) 'ext_hdr' (line 487) <== Memory access at offset 34 
>>> overflows this variable
>>>   HINT: this may be a false positive if your program uses some custom stack 
>>> unwind mechanism, swapcontext or vfork
>>>         (longjmp and C++ exceptions *are* supported)
>>>   SUMMARY: AddressSanitizer: stack-buffer-overflow net/eth.c:410:17 in 
>>> _eth_get_rss_ex_dst_addr
>>>   Shadow bytes around the buggy address:
>>>     0x10003df188d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df188e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df188f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18910: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
>>>   =>0x10003df18920:[02]f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18930: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18940: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18950: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18960: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>     0x10003df18970: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>>>   Shadow byte legend (one shadow byte represents 8 application bytes):
>>>     Addressable:           00
>>>     Partially addressable: 01 02 03 04 05 06 07
>>>     Stack left redzone:      f1
>>>     Stack right redzone:     f3
>>>   ==2859770==ABORTING
>>>
>>> Add the corresponding qtest case with the fuzzer reproducer.
>>>
>>> FWIW GCC 11 similarly reported:
>>>
>>>   net/eth.c: In function 'eth_parse_ipv6_hdr':
>>>   net/eth.c:410:15: error: array subscript 'struct ip6_ext_hdr_routing[0]' 
>>> is partly outside array bounds of 'struct ip6_ext_hdr[1]' 
>>> [-Werror=array-bounds]
>>>     410 |     if ((rthdr->rtype == 2) && (rthdr->segleft == 1)) {
>>>         |          ~~~~~^~~~~~~
>>>   net/eth.c:485:24: note: while referencing 'ext_hdr'
>>>     485 |     struct ip6_ext_hdr ext_hdr;
>>>         |                        ^~~~~~~
>>>   net/eth.c:410:38: error: array subscript 'struct ip6_ext_hdr_routing[0]' 
>>> is partly outside array bounds of 'struct ip6_ext_hdr[1]' 
>>> [-Werror=array-bounds]
>>>     410 |     if ((rthdr->rtype == 2) && (rthdr->segleft == 1)) {
>>>         |                                 ~~~~~^~~~~~~~~
>>>   net/eth.c:485:24: note: while referencing 'ext_hdr'
>>>     485 |     struct ip6_ext_hdr ext_hdr;
>>>         |                        ^~~~~~~
>>>
>>> Cc: qemu-stable@nongnu.org
>>> Buglink: https://bugs.launchpad.net/qemu/+bug/1879531
>>> Reported-by: Alexander Bulekov <alxndr@bu.edu>
>>> Reported-by: Miroslav Rezanina <mrezanin@redhat.com>
>>> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
>>> Fixes: eb700029c78 ("net_pkt: Extend packet abstraction as required by 
>>> e1000e functionality")
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> ---
>>>  net/eth.c                      | 13 +++++----
>>>  tests/qtest/fuzz-e1000e-test.c | 53 ++++++++++++++++++++++++++++++++++
>>>  MAINTAINERS                    |  1 +
>>>  tests/qtest/meson.build        |  1 +
>>>  4 files changed, 63 insertions(+), 5 deletions(-)
>>>  create mode 100644 tests/qtest/fuzz-e1000e-test.c