Re: [PULL 18/40] linux-user: Fix types in uaccess.c

[Laurent Vivier]

Le 10/03/2021 à 16:48, Peter Maydell a écrit :
> On Fri, 19 Feb 2021 at 09:21, Laurent Vivier <laurent@vivier.eu> wrote:
>>
>> Hi Richard,
>>
>> I think this commit is the cause of CID 1446711.
>>
>> There is no concistancy between the various declarations of unlock_user():
>>
>> bsd-user/qemu.h
>>
>> static inline void unlock_user(void *host_ptr, abi_ulong guest_addr,
>>                                long len)
>>
>> include/exec/softmmu-semi.h
>>
>> static void softmmu_unlock_user(CPUArchState *env, void *p, target_ulong 
>> addr,
>>                                 target_ulong len)
>> ...
>> #define unlock_user(s, args, len) softmmu_unlock_user(env, s, args, len)
>>
>> linux-user/qemu.h
>>
>> #ifndef DEBUG_REMAP
>> static inline void unlock_user(void *host_ptr, abi_ulong guest_addr, size_t 
>> len)
>> { }
>> #else
>> void unlock_user(void *host_ptr, abi_ulong guest_addr, long len);
>> #endif
>>
>> To take a signed long here allows to unconditionnaly call the unlock_user() 
>> function after the
>> syscall and not to copy the buffer if the value is negative.
> 
> Hi; what was the conclusion here about how best to fix the Coverity issue?

For what I know, there is no conclusion.

> To save people looking it up, Coverity complains because in the
> TARGET_NR_readlinkat case for linux-user we do:
>             void *p2;
>             p  = lock_user_string(arg2);
>             p2 = lock_user(VERIFY_WRITE, arg3, arg4, 0);
>             if (!p || !p2) {
>                 ret = -TARGET_EFAULT;
>             } else if (is_proc_myself((const char *)p, "exe")) {
>                 char real[PATH_MAX], *temp;
>                 temp = realpath(exec_path, real);
>                 ret = temp == NULL ? get_errno(-1) : strlen(real) ;
>                 snprintf((char *)p2, arg4, "%s", real);
>             } else {
>                 ret = get_errno(readlinkat(arg1, path(p), p2, arg4));
>             }
>             unlock_user(p2, arg3, ret);
>             unlock_user(p, arg2, 0);
> 
> and in the "ret = -TARGET_EFAULT" and also the get_errno(readlinkat(...))
> codepaths we can set ret to a negative number, which Coverity thinks
> is suspicious given that unlock_user()'s new prototype says it
> is an unsigned value. It's correct to be suspicious, because we really
> did change from doing a >=0 to a !=0 check on the length.
> 
> Unless we really want to audit all the unlock_user() callsites,
> going back to the previous semantics seems sensible.

I agree with that.

Thanks,
Laurent