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

[Alexander Bulekov]

On 210317 1742, Philippe Mathieu-Daudé wrote:
> 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?

It was private, but I just CC-ed you on the response. Since this
predates the switch to qemu-security@nongnu.org, maybe it's not as much
of a problem anymore

> 
> 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
>