Re: [PATCH-for-5.0] qga-posix: Avoid crashing process when failing to allocate memory

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/25/20 7:19 AM, Dietmar Maurer wrote:
> but error_setg() also calls malloc, so this does not help at all?

IIUC the problem, you can send a QMP command to ask to read let's say 
3GB of a file, and QEMU crashes. But this doesn't mean there the .heap 
is empty, there is probably few bytes still available, enough to respond 
with an error message.

> 
>> On March 24, 2020 8:48 PM Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>>
>>   
>> Similarly to commit 807e2b6fce0 for Windows, kindly return a
>> QMP error message instead of crashing the whole process.
>>
>> Cc: qemu-stable@nongnu.org
>> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1594054
>> Reported-by: Fakhri Zulkifli <mohdfakhrizulkifli@gmail.com>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>   qga/commands-posix.c | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
>> index 93474ff770..8f127788e6 100644
>> --- a/qga/commands-posix.c
>> +++ b/qga/commands-posix.c
>> @@ -493,7 +493,13 @@ struct GuestFileRead *qmp_guest_file_read(int64_t handle, bool has_count,
>>           gfh->state = RW_STATE_NEW;
>>       }
>>   
>> -    buf = g_malloc0(count+1);
>> +    buf = g_try_malloc0(count + 1);
>> +    if (!buf) {
>> +        error_setg(errp,
>> +                   "failed to allocate sufficient memory "
>> +                   "to complete the requested service");
>> +        return NULL;
>> +    }
>>       read_count = fread(buf, 1, count, fh);
>>       if (ferror(fh)) {
>>           error_setg_errno(errp, errno, "failed to read file");
>> -- 
>> 2.21.1
>