Re: [Qemu-devel] [PATCH v1 for 3.0 1/2] linux-user/mmap.c: handle len = 0 maps correctly

[Alex Bennée]

Laurent Vivier <address@hidden> writes:

> Le 26/07/2018 à 15:29, Alex Bennée a écrit:
>> I've slightly re-organised the check to more closely match the
>> sequence that the kernel uses in do_mmap().
>>
>> Signed-off-by: Alex Bennée <address@hidden>
>> Cc: umarcor <address@hidden>
>> ---
>>  linux-user/mmap.c | 14 +++++++++++---
>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
>> index d0c50e4888..3ef69fa2d0 100644
>> --- a/linux-user/mmap.c
>> +++ b/linux-user/mmap.c
>> @@ -391,14 +391,22 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, 
>> int prot,
>>      }
>>  #endif
>>
>> -    if (offset & ~TARGET_PAGE_MASK) {
>> +    if (!len) {
>>          errno = EINVAL;
>>          goto fail;
>>      }
>>
>>      len = TARGET_PAGE_ALIGN(len);
>> -    if (len == 0)
>> -        goto the_end;
>> +    if (!len) {
>> +        errno = EINVAL;
>> +        goto fail;
>> +    }
>
> Why do you check twice len?
> TARGET_PAGE_ALIGN() rounds up the value, so if it was not 0, it cannot
> be now.

I was trying to follow the kernel style but I realise TARGET_PAGE_ALIGN
might be a different test compared to the kernel's PAGE_ALIGN(len) for
overflows:

        if (!len)
                return -EINVAL;

        /*
         * Does the application expect PROT_READ to imply PROT_EXEC?
         *
         * (the exception is when the underlying filesystem is noexec
         *  mounted, in which case we dont add PROT_EXEC.)
         */
        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                if (!(file && path_noexec(&file->f_path)))
                        prot |= PROT_EXEC;

        /* force arch specific MAP_FIXED handling in get_unmapped_area */
        if (flags & MAP_FIXED_NOREPLACE)
                flags |= MAP_FIXED;

        if (!(flags & MAP_FIXED))
                addr = round_hint_to_min(addr);

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len)
                return -ENOMEM;


>
> Thanks,
> Laurent


--
Alex Bennée