linux-kernel - Re: [PATCH] assoc_array: Avoid open coded arithmetic in allocator arguments

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Date:   Tue, 21 Sep 2021 13:30:37 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Len Baker <len.baker@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] assoc_array: Avoid open coded arithmetic in allocator
 arguments



On 9/19/21 06:09, Len Baker wrote:
> As noted in the "Deprecated Interfaces, Language Features, Attributes,
> and Conventions" documentation [1], size calculations (especially
> multiplication) should not be performed in memory allocator (or similar)
> function arguments due to the risk of them overflowing. This could lead
> to values wrapping around and a smaller allocation being made than the
> caller was expecting. Using those allocations could lead to linear
> overflows of heap memory and other misbehaviors.
> 
> So, use the struct_size() helper to do the arithmetic instead of the
> argument "size + count * size" in the kmalloc() and kzalloc() functions.
> 
> Also, take the opportunity to refactor the memcpy() calls to use the
> struct_size() and flex_array_size() helpers.
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments
> 
> Signed-off-by: Len Baker <len.baker@....com>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

I'll add this to my -next tree.

Thanks
--
Gustavo

> ---
>  lib/assoc_array.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/assoc_array.c b/lib/assoc_array.c
> index 04c98799c3ba..079c72e26493 100644
> --- a/lib/assoc_array.c
> +++ b/lib/assoc_array.c
> @@ -741,8 +741,7 @@ static bool assoc_array_insert_into_terminal_node(struct assoc_array_edit *edit,
>  	keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
>  	keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
> 
> -	new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
> -			 keylen * sizeof(unsigned long), GFP_KERNEL);
> +	new_s0 = kzalloc(struct_size(new_s0, index_key, keylen), GFP_KERNEL);
>  	if (!new_s0)
>  		return false;
>  	edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s0);
> @@ -849,8 +848,8 @@ static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
>  		keylen = round_up(diff, ASSOC_ARRAY_KEY_CHUNK_SIZE);
>  		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
> 
> -		new_s0 = kzalloc(sizeof(struct assoc_array_shortcut) +
> -				 keylen * sizeof(unsigned long), GFP_KERNEL);
> +		new_s0 = kzalloc(struct_size(new_s0, index_key, keylen),
> +				 GFP_KERNEL);
>  		if (!new_s0)
>  			return false;
>  		edit->new_meta[1] = assoc_array_shortcut_to_ptr(new_s0);
> @@ -864,7 +863,7 @@ static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
>  		new_n0->parent_slot = 0;
> 
>  		memcpy(new_s0->index_key, shortcut->index_key,
> -		       keylen * sizeof(unsigned long));
> +		       flex_array_size(new_s0, index_key, keylen));
> 
>  		blank = ULONG_MAX << (diff & ASSOC_ARRAY_KEY_CHUNK_MASK);
>  		pr_devel("blank off [%zu] %d: %lx\n", keylen - 1, diff, blank);
> @@ -899,8 +898,8 @@ static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
>  		keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
>  		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
> 
> -		new_s1 = kzalloc(sizeof(struct assoc_array_shortcut) +
> -				 keylen * sizeof(unsigned long), GFP_KERNEL);
> +		new_s1 = kzalloc(struct_size(new_s1, index_key, keylen),
> +				 GFP_KERNEL);
>  		if (!new_s1)
>  			return false;
>  		edit->new_meta[2] = assoc_array_shortcut_to_ptr(new_s1);
> @@ -913,7 +912,7 @@ static bool assoc_array_insert_mid_shortcut(struct assoc_array_edit *edit,
>  		new_n0->slots[sc_slot] = assoc_array_shortcut_to_ptr(new_s1);
> 
>  		memcpy(new_s1->index_key, shortcut->index_key,
> -		       keylen * sizeof(unsigned long));
> +		       flex_array_size(new_s1, index_key, keylen));
> 
>  		edit->set[1].ptr = &side->back_pointer;
>  		edit->set[1].to = assoc_array_shortcut_to_ptr(new_s1);
> @@ -1490,13 +1489,12 @@ int assoc_array_gc(struct assoc_array *array,
>  		shortcut = assoc_array_ptr_to_shortcut(cursor);
>  		keylen = round_up(shortcut->skip_to_level, ASSOC_ARRAY_KEY_CHUNK_SIZE);
>  		keylen >>= ASSOC_ARRAY_KEY_CHUNK_SHIFT;
> -		new_s = kmalloc(sizeof(struct assoc_array_shortcut) +
> -				keylen * sizeof(unsigned long), GFP_KERNEL);
> +		new_s = kmalloc(struct_size(new_s, index_key, keylen),
> +				GFP_KERNEL);
>  		if (!new_s)
>  			goto enomem;
>  		pr_devel("dup shortcut %p -> %p\n", shortcut, new_s);
> -		memcpy(new_s, shortcut, (sizeof(struct assoc_array_shortcut) +
> -					 keylen * sizeof(unsigned long)));
> +		memcpy(new_s, shortcut, struct_size(new_s, index_key, keylen));
>  		new_s->back_pointer = new_parent;
>  		new_s->parent_slot = shortcut->parent_slot;
>  		*new_ptr_pp = new_parent = assoc_array_shortcut_to_ptr(new_s);
> --
> 2.25.1
>