Re: [PATCH] tools/xenstored: Don't assume errno will not be overwritten in lu_arch()

[Juergen Gross <jgross@suse.com>]

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On 29.07.21 17:23, Julien Grall wrote:
> 
> 
> On 29/07/2021 12:06, Julien Grall wrote:
>> From: Julien Grall <jgrall@amazon.com>
>>
>> At the moment, do_control_lu() will set errno to 0 before calling
>> lu_arch() and then check errno. The expectation is nothing in lu_arch()
>> will change the value unless there is an error.
>>
>> However, per errno(3), a function that succeeds is allowed to change
>> errno. In fact, syslog() will overwrite errno if the logs are rotated
>> at the time it is called.
>>
>> To prevent any further issue, errno is now always set before
>> returning NULL.
>>
>> Additionally, errno is only checked when returning NULL so the client
>> can see the error message if there is any.
>>
>> Reported-by: Michael Kurth <mku@amazon.com>
>> Signed-off-by: Julien Grall <jgrall@amazon.com>
>> ---
>>   tools/xenstore/xenstored_control.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/tools/xenstore/xenstored_control.c 
>> b/tools/xenstore/xenstored_control.c
>> index 6b68b79faac7..6fcb42095b59 100644
>> --- a/tools/xenstore/xenstored_control.c
>> +++ b/tools/xenstore/xenstored_control.c
>> @@ -324,6 +324,7 @@ static const char *lu_binary_alloc(const void 
>> *ctx, struct connection *conn,
>>       lu_status->kernel_size = size;
>>       lu_status->kernel_off = 0;
>> +    errno = 0;
>>       return NULL;
>>   }
>> @@ -339,6 +340,7 @@ static const char *lu_binary_save(const void *ctx, 
>> struct connection *conn,
>>       memcpy(lu_status->kernel + lu_status->kernel_off, data, size);
>>       lu_status->kernel_off += size;
>> +    errno = 0;
>>       return NULL;
>>   }
> 
> I forgot to update lu_binary(). I will respin the patch once I get some 
> feedback.

With setting errno to 0 before returning NULL in lu_binary() you can add

Reviewed-by: Juergen Gross <jgross@suse.com>


Juergen


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