Re: [Qemu-devel] [PATCH] migration: Replace strncpy() by g_strlcpy()

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/08/2018 04:56, Philippe Mathieu-Daudé wrote:
> Fedora 29 comes with GCC 8.1 which added the 'stringop-truncation' checks.
> 
> Replace the strncpy() calls by g_strlcpy() to avoid the following warning:
> 
>   migration/global_state.c: In function 'global_state_store_running':
>   migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>        strncpy((char *)global_state.runstate,
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>               state, sizeof(global_state.runstate));
>               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Reported-by: Howard Spoelstra <hsp.cat7@gmail.com>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> See http://lists.nongnu.org/archive/html/qemu-devel/2018-07/msg03723.html
> 
>  migration/global_state.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 8e8ab5c51e..d5df502cd5 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -42,7 +42,7 @@ int global_state_store(void)
>  void global_state_store_running(void)
>  {
>      const char *state = RunState_str(RUN_STATE_RUNNING);
> -    strncpy((char *)global_state.runstate,
> +    g_strlcpy((char *)global_state.runstate,
>             state, sizeof(global_state.runstate));
>  }
>  
> 

This is wrong because strlcpy doesn't zero the rest of
global_state.runstate, so you could end up with something like
"running\0ate\0\0..." in global_state.runstate However, the same mistake
is already present in vl.c's runstate_store.

Juan, David, what to do?  strncpy is easy to misuse, but we do have
cases where it's correct and it should tingle the reviewers' spidey
senses...  I wouldn't mind disabling the warning, and using strncpy in
runstate_store, because in practice it's already reported by Coverity
and it can be shut up there.

Thanks,

Paolo