Re: [Qemu-devel] [PATCH 7/8] migration: fix unbounded stack for source_return_path_thread

[Paolo Bonzini <pbonzini@redhat.com>]

On 08/03/2016 10:48, Juan Quintela wrote:
> Peter Xu <peterx@redhat.com> wrote:
>> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
>> CC: Juan Quintela <quintela@redhat.com>
>> CC: Amit Shah <amit.shah@redhat.com>
>> Signed-off-by: Peter Xu <peterx@redhat.com>
>> ---
>>  migration/migration.c | 7 ++++---
>>  1 file changed, 4 insertions(+), 3 deletions(-)
>>
>> diff --git a/migration/migration.c b/migration/migration.c
>> index 0129d9f..f1a3976 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -1265,11 +1265,11 @@ static void migrate_handle_rp_req_pages(MigrationState *ms, const char* rbname,
>>   */
>>  static void *source_return_path_thread(void *opaque)
>>  {
>> +#define __MAX_LEN (512)
>>      MigrationState *ms = opaque;
>>      QEMUFile *rp = ms->rp_state.from_dst_file;
>>      uint16_t header_len, header_type;
>> -    const int max_len = 512;
>> -    uint8_t buf[max_len];
>> +    uint8_t buf[__MAX_LEN];
>>      uint32_t tmp32, sibling_error;
>>      ram_addr_t start = 0; /* =0 to silence warning */
>>      size_t  len = 0, expected_len;
>> @@ -1292,7 +1292,7 @@ static void *source_return_path_thread(void *opaque)
>>  
>>          if ((rp_cmd_args[header_type].len != -1 &&
>>              header_len != rp_cmd_args[header_type].len) ||
>> -            header_len > max_len) {
>> +            header_len > __MAX_LEN) {
>>              error_report("RP: Received '%s' message (0x%04x) with"
>>                      "incorrect length %d expecting %zu",
>>                      rp_cmd_args[header_type].name, header_type, header_len,
>> @@ -1372,6 +1372,7 @@ out:
>>      ms->rp_state.from_dst_file = NULL;
>>      qemu_fclose(rp);
>>      return NULL;
>> +#undef __MAX_LEN
>>  }
>>  
>>  static int open_return_path_on_source(MigrationState *ms)
> 
> Reviewed-by: Juan Quintela <quintela@redhat.com>

Not really, because __ is restricted by the C standard and should not be
used in QEMU (besides the problems pointed out by other reviewers for
other patches in the series).

Paolo