Re: [Qemu-devel] [PATCH v2] linux-user: avoid string truncation warnings in uname field copying

[Philippe Mathieu-Daudé]

On 5/1/19 4:46 PM, Daniel P. Berrangé wrote:
> In file included from /usr/include/string.h:494,
>                  from include/qemu/osdep.h:101,
>                  from linux-user/uname.c:20:
> In function ‘strncpy’,
>     inlined from ‘sys_uname’ at linux-user/uname.c:94:3:
> /usr/include/bits/string_fortified.h:106:10: warning: ‘__builtin_strncpy’ 
> output may be truncated copying 64 bytes from a string of length 64 
> [-Wstringop-truncation]
>   106 |   return __builtin___strncpy_chk (__dest, __src, __len, __bos 
> (__dest));
>       |          
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> We don't care where the NUL terminator in the original uname
> field was. It suffices to copy the entire original field and
> simply force a NUL terminator at the end of the new field.
> 
> Signed-off-by: Daniel P. Berrangé <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
> 
> Changed in v2:
> 
>  - Always use sizeof() in preference to __NEW_UTS_LEN
> 
>  linux-user/uname.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/linux-user/uname.c b/linux-user/uname.c
> index 313b79dbad..1c05f95387 100644
> --- a/linux-user/uname.c
> +++ b/linux-user/uname.c
> @@ -72,9 +72,8 @@ const char *cpu_to_uname_machine(void *cpu_env)
>  
>  #define COPY_UTSNAME_FIELD(dest, src) \
>    do { \
> -      /* __NEW_UTS_LEN doesn't include terminating null */ \
> -      (void) strncpy((dest), (src), __NEW_UTS_LEN); \
> -      (dest)[__NEW_UTS_LEN] = '\0'; \
> +      memcpy((dest), (src), MIN(sizeof(src), sizeof(dest))); \
> +      (dest)[sizeof(dest) - 1] = '\0'; \
>    } while (0)
>  
>  int sys_uname(struct new_utsname *buf)
>