Re: [PATCH-for-5.2 1/3] fuzz: fix writing DMA patterns

[Alexander Bulekov]

On 201029 1328, Alexander Bulekov wrote:
> This code had all sorts of issues. We used a loop similar to
> address_space_write_rom, but I did not remove a "break" that only made
> sense in the context of the switch statement in the original code. Then,
> after the loop, we did a separate qtest_memwrite over the entire DMA
> access range, defeating the purpose of the loop. Additionally, we
> increment the buf pointer, and then try to g_free() it. Fix these
> problems.
> 
> Reported-by: OSS-Fuzz (Issue 26725)

Also:
Reported-by: OSS-Fuzz (Issue 26691)

> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> ---
>  tests/qtest/fuzz/generic_fuzz.c | 37 +++++++++++++++------------------
>  1 file changed, 17 insertions(+), 20 deletions(-)
> 
> diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
> index a8f5864883..3e2d50feaa 100644
> --- a/tests/qtest/fuzz/generic_fuzz.c
> +++ b/tests/qtest/fuzz/generic_fuzz.c
> @@ -229,10 +229,10 @@ void fuzz_dma_read_cb(size_t addr, size_t len, 
> MemoryRegion *mr, bool is_write)
>      address_range ar = {addr, len};
>      g_array_append_val(dma_regions, ar);
>      pattern p = g_array_index(dma_patterns, pattern, dma_pattern_index);
> -    void *buf = pattern_alloc(p, ar.size);
> +    void *buf_base = pattern_alloc(p, ar.size);
> +    void *buf = buf_base;
>      hwaddr l, addr1;
>      MemoryRegion *mr1;
> -    uint8_t *ram_ptr;
>      while (len > 0) {
>          l = len;
>          mr1 = address_space_translate(first_cpu->as,
> @@ -244,30 +244,27 @@ void fuzz_dma_read_cb(size_t addr, size_t len, 
> MemoryRegion *mr, bool is_write)
>              l = memory_access_size(mr1, l, addr1);
>          } else {
>              /* ROM/RAM case */
> -            ram_ptr = qemu_map_ram_ptr(mr1->ram_block, addr1);
> -            memcpy(ram_ptr, buf, l);
> -            break;
> +            if (qtest_log_enabled) {
> +                /*
> +                * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix 
> the log
> +                * that will be written by qtest.c with a DMA tag, so we can 
> reorder
> +                * the resulting QTest trace so the DMA fills precede the 
> last PIO/MMIO
> +                * command.
> +                */
> +                fprintf(stderr, "[DMA] ");
> +                if (double_fetch) {
> +                    fprintf(stderr, "[DOUBLE-FETCH] ");
> +                }
> +                fflush(stderr);
> +            }
> +            qtest_memwrite(qts_global, addr, buf, l);
>          }
>          len -= l;
>          buf += l;
>          addr += l;
>  
>      }
> -    if (qtest_log_enabled) {
> -        /*
> -         * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix the log
> -         * that will be written by qtest.c with a DMA tag, so we can reorder
> -         * the resulting QTest trace so the DMA fills precede the last 
> PIO/MMIO
> -         * command.
> -         */
> -        fprintf(stderr, "[DMA] ");
> -        if (double_fetch) {
> -            fprintf(stderr, "[DOUBLE-FETCH] ");
> -        }
> -        fflush(stderr);
> -    }
> -    qtest_memwrite(qts_global, ar.addr, buf, ar.size);
> -    g_free(buf);
> +    g_free(buf_base);
>  
>      /* Increment the index of the pattern for the next DMA access */
>      dma_pattern_index = (dma_pattern_index + 1) % dma_patterns->len;
> -- 
> 2.28.0
>