Re: [Qemu-devel] [PATCH] target-ppc: kvm: Fix memory overflow issue about strncat()

[Alexander Graf <agraf@suse.de>]

On 13.10.14 16:36, Chen Gang wrote:
> strncat() will append additional '\0' to destination buffer, so need
> additional 1 byte for it, or may cause memory overflow, just like other
> area within QEMU have done.
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>

I agree with this patch. However, the code is pretty ugly - I'm sure it
must've been me who wrote it :).

Could you please instead rewrite it to use g_strdup_printf() rather than
strncat()s? That way we resolve all string pitfalls automatically - and
this code is not the fast path, so doing an extra memory allocation is ok.


Alex

> ---
>  target-ppc/kvm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/kvm.c b/target-ppc/kvm.c
> index 9c23c6b..66e7ce5 100644
> --- a/target-ppc/kvm.c
> +++ b/target-ppc/kvm.c
> @@ -1794,8 +1794,8 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
>          return -1;
>      }
>  
> -    strncat(buf, "/", sizeof(buf) - strlen(buf));
> -    strncat(buf, propname, sizeof(buf) - strlen(buf));
> +    strncat(buf, "/", sizeof(buf) - strlen(buf) - 1);
> +    strncat(buf, propname, sizeof(buf) - strlen(buf) - 1);
>  
>      f = fopen(buf, "rb");
>      if (!f) {
>