Re: [Qemu-devel] [PATCH for-2.12] gdbstub: fix off-by-one in gdb_handle_packet()

[Stefan Hajnoczi]

On Sun, Apr 08, 2018 at 11:59:33AM -0300, Philippe Mathieu-Daudé wrote:
> memtohex() adds an extra trailing NUL character.
> 
> Reported-by: AddressSanitizer
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
> (gdb) dump binary memory /tmp/dram.bin 0x94000000 0x94100000
> Remote connection closed
> 
> =================================================================
> ==22732==ERROR: AddressSanitizer: stack-buffer-overflow on address 
> 0x7ffe43018340 at pc 0x55f2655fde81 bp 0x7ffe43017210 sp 0x7ffe43017208
> WRITE of size 1 at 0x7ffe43018340 thread T0
>     #0 0x55f2655fde80 in memtohex /source/qemu/gdbstub.c:520
>     #1 0x55f26560254d in gdb_handle_packet /source/qemu/gdbstub.c:1140
>     #2 0x55f2656073c3 in gdb_read_byte /source/qemu/gdbstub.c:1703
>     #3 0x55f2656076a7 in gdb_chr_receive /source/qemu/gdbstub.c:1909
>     #4 0x55f266457656 in qemu_chr_be_write_impl 
> /source/qemu/chardev/char.c:175
>     #5 0x55f2664576f9 in qemu_chr_be_write /source/qemu/chardev/char.c:187
>     #6 0x55f26646f6f0 in tcp_chr_read /source/qemu/chardev/char-socket.c:470
>     #7 0x55f2664bc9e3 in qio_channel_fd_source_dispatch 
> /source/qemu/io/channel-watch.c:84
>     #8 0x7f17d01b30f4 in g_main_context_dispatch 
> (/usr/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x4c0f4)
>     #9 0x55f2665c7f10 in glib_pollfds_poll /source/qemu/util/main-loop.c:215
>     #10 0x55f2665c8100 in os_host_main_loop_wait 
> /source/qemu/util/main-loop.c:263
>     #11 0x55f2665c82d6 in main_loop_wait /source/qemu/util/main-loop.c:522
>     #12 0x55f26599e13b in main_loop /source/qemu/vl.c:1943
>     #13 0x55f2659b0869 in main /source/qemu/vl.c:4734
> 
> Address 0x7ffe43018340 is located in stack of thread T0 at offset 4192 in 
> frame
>     #0 0x55f265601266 in gdb_handle_packet /source/qemu/gdbstub.c:996
> 
>   This frame has 3 object(s):
>     [32, 40) 'p'
>     [96, 4192) 'buf' <== Memory access at offset 4192 overflows this variable
>     [4224, 8320) 'mem_buf'
> SUMMARY: AddressSanitizer: stack-buffer-overflow /source/qemu/gdbstub.c:520 
> in memtohex
> Shadow bytes around the buggy address:
>   0x1000485fb010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> =>0x1000485fb060: 00 00 00 00 00 00 00 00[f2]f2 f2 f2 00 00 00 00
>   0x1000485fb070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb0a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>   0x1000485fb0b0: 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
>   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
> ==22732==ABORTING
> ---
>  gdbstub.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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