linux-kernel - Re: [PATCH] staging: android: Replace strcpy with strlcpy

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Message-ID: <20170312005944.GL29622@ZenIV.linux.org.uk>
Date:   Sun, 12 Mar 2017 00:59:44 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     simran singhal <singhalsimran0@...il.com>
Cc:     gregkh@...uxfoundation.org, arve@...roid.com,
        riandrews@...roid.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [PATCH] staging: android: Replace strcpy with strlcpy

On Sun, Mar 12, 2017 at 02:10:01AM +0530, simran singhal wrote:
> Replace strcpy with strlcpy as strcpy does not check for buffer
> overflow.
> This is found using Flawfinder.
> 
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
> ---
>  drivers/staging/android/ashmem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> index 7cbad0d..eb2f4ef 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -548,7 +548,8 @@ static int set_name(struct ashmem_area *asma, void __user *name)
>  	if (unlikely(asma->file))
>  		ret = -EINVAL;
>  	else
> -		strcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name);
> +		strlcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name,
> +			sizeof(asma->name + ASHMEM_NAME_PREFIX_LEN));

Trivial C quiz: given

struct ashmem_area {
        char name[ASHMEM_FULL_NAME_LEN];
        struct list_head unpinned_list;
        struct file *file;
        size_t size;
        unsigned long prot_mask;
};
static int set_name(struct ashmem_area *asma, void __user *name)

what, in your opinion, would be
	1) type of asma->name
	2) type of asma->name + ASHMEM_NAME_PREFIX_LEN
	3) value of sizeof(asma->name + ASHMEM_NAME_PREFIX_LEN)
As a bonus question,
	4) what is the value of this kind of patches?

<rot13 answers>
	1) NFUZRZ_SHYY_ANZR_YRA-ryrzrag neenl bs pune
	2) cbvagre gb pune
	3) fvmr bs n cbvagre
	4) fbpvbybtvpny - ernql-znqr vyyhfgengvbaf bs crevyf bs
pnetb phyg.