linux-kernel - Re: [PATCH v4 1/4] mm/mlock: return EINVAL if len overflows for mlock/munlock

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Message-ID: <27b9cb5b-0118-f989-80c2-6a143a4232af@redhat.com>
Date:   Mon, 20 Mar 2023 11:54:11 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Wupeng Ma <mawupeng1@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kuleshovmail@...il.com, aneesh.kumar@...ux.ibm.com
Subject: Re: [PATCH v4 1/4] mm/mlock: return EINVAL if len overflows for
 mlock/munlock

On 20.03.23 03:47, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> While testing mlock, we have a problem if the len of mlock is ULONG_MAX.
> The return value of mlock is zero. But nothing will be locked since the
> len in do_mlock overflows to zero due to the following code in mlock:
> 
>    len = PAGE_ALIGN(len + (offset_in_page(start)));
> 
> The same problem happens in munlock.
> 
> Add new check and return -EINVAL to fix this overflowing scenarios since
> they are absolutely wrong.

Thinking again, wouldn't we reject mlock(0, ULONG_MAX) now as well?

> 
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> ---
>   mm/mlock.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 617469fce96d..eb68476da497 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -568,6 +568,7 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>   	unsigned long locked;
>   	unsigned long lock_limit;
>   	int error = -ENOMEM;
> +	size_t old_len = len;
>   
>   	start = untagged_addr(start);
>   
> @@ -577,6 +578,9 @@ static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t fla
>   	len = PAGE_ALIGN(len + (offset_in_page(start)));
>   	start &= PAGE_MASK;
>   
> +	if (old_len != 0 && len == 0)

if (old_len && !len)

> +		return -EINVAL;
> +
>   	lock_limit = rlimit(RLIMIT_MEMLOCK);
>   	lock_limit >>= PAGE_SHIFT;
>   	locked = len >> PAGE_SHIFT;
> @@ -631,12 +635,16 @@ SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
>   SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
>   {
>   	int ret;
> +	size_t old_len = len;
>   
>   	start = untagged_addr(start);
>   
>   	len = PAGE_ALIGN(len + (offset_in_page(start)));
>   	start &= PAGE_MASK;
>   
> +	if (old_len != 0 && len == 0)

if (old_len && !len)

> +		return -EINVAL;
> +
>   	if (mmap_write_lock_killable(current->mm))
>   		return -EINTR;
>   	ret = apply_vma_lock_flags(start, len, 0);

-- 
Thanks,

David / dhildenb