Re: [Qemu-devel] [PATCH 01/38] exec: Fix memory allocation when memory path names new file

[Markus Armbruster]

Paolo Bonzini <address@hidden> writes:

> On 29/02/2016 19:40, Markus Armbruster wrote:
>> -    if (!stat(path, &st) && S_ISDIR(st.st_mode)) {
>> +    ret = stat(path, &st);
>> +    if (!ret && S_ISDIR(st.st_mode)) {
>> +        /* path names a directory -> create a temporary file there */
>>          /* Make name safe to use with mkstemp by replacing '/' with '_'. */
>>          sanitized_name = g_strdup(memory_region_name(block->mr));
>>          for (c = sanitized_name; *c != '\0'; c++) {
>> @@ -1282,13 +1271,32 @@ static void *file_ram_alloc(RAMBlock *block,
>>              unlink(filename);
>>          }
>>          g_free(filename);
>> +    } else if (!ret) {
>> +        /* path names an existing file -> use it */
>> +        fd = open(path, O_RDWR);
>>      } else {
>> +        /* create a new file */
>>          fd = open(path, O_RDWR | O_CREAT, 0644);
>> +        unlink_on_error = true;
>>      }
>
> While at it, let's avoid TOCTTOU conditions:
>
>     for (;;) {
>         fd = open(path, O_RDWR);
>         if (fd != -1) {
>             break;
>         }
>         if (errno == ENOENT) {
>             fd = open(path, O_RDWR | O_CREAT | O_EXCL, 0644);
>             if (fd != -1) {
>                 unlink_on_error = true;
>                 break;
>             }
>         } else if (errno == EISDIR) {
>             ... mkstemp ...
>             if (fd != -1) {
>                 unlink_on_error = true;
>                 break;
>             }
>         }
>         if (errno != EEXIST && errno != EINTR) {
>             goto error;
>         }
>     }
>
> and use fstatfs in gethugepagesize.

Good point, will do!