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Re: [Qemu-trivial] [Qemu-devel] [PATCH] syscall: fix compiler warnings (


From: Laurent Vivier
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] syscall: fix compiler warnings (clang 5)
Date: Wed, 10 May 2017 14:32:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 06/05/2017 02:41, Philippe Mathieu-Daudé wrote:
> static code analyzer complain:
> 
> linux-user/syscall.c:5575:9: warning: Dereference of undefined pointer value
>     if (*host_rt_dev_ptr != 0) {
>         ^~~~~~~~~~~~~~~~
> 
> Reported-by: Clang Static Analyzer
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  linux-user/syscall.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index cec8428589..c541e22693 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5526,7 +5526,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, 
> uint8_t *buf_temp,
>      int target_size;
>      void *argptr;
>      abi_ulong *target_rt_dev_ptr;
> -    unsigned long *host_rt_dev_ptr;
> +    unsigned long *host_rt_dev_ptr = NULL;
>      abi_long ret;
>      int i;
>  
> @@ -5572,7 +5572,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, 
> uint8_t *buf_temp,
>      unlock_user(argptr, arg, 0);
>  
>      ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));

I think we should "assert(host_rt_dev_ptr)" here. It's a bug if
host_rt_dev_ptr is not set.

The "for" loop scans the structure to find the rt_dev field, and we
should always enter in the first "if", so "host_rt_dev_ptr" is always set.

> -    if (*host_rt_dev_ptr != 0) {
> +    if (host_rt_dev_ptr != NULL && *host_rt_dev_ptr != 0) {
>          unlock_user((void *)*host_rt_dev_ptr,
>                      *target_rt_dev_ptr, 0);
>      }
> 

Laurent



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