2018-06-04 07:06:30

by Xiaoming Ni

Subject: [PATCH] net/dns_resolver: dns_query Modify parameter checking to avoid dead code

After commit 1a4240f4764a ("DNS: Separate out CIFS DNS Resolver code")
a dead code exists in function dns_query

code show as below:
if (!name || namelen == 0)
return -EINVAL;
/*Now the value of "namelen" cannot be equal to 0*/
....
if (!namelen) /*The condition "!namelen"" cannot be true*/
namelen = strnlen(name, 256); /*deadcode*/

Modify parameter checking to avoid dead code

Signed-off-by: nixiaoming <[email protected]>
---
net/dns_resolver/dns_query.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
index 49da670..f2acee2 100644
--- a/net/dns_resolver/dns_query.c
+++ b/net/dns_resolver/dns_query.c
@@ -81,7 +81,9 @@ int dns_query(const char *type, const char *name, size_t namelen,
kenter("%s,%*.*s,%zu,%s",
type, (int)namelen, (int)namelen, name, namelen, options);

- if (!name || namelen == 0)
+ if (!name || namelen < 3 || namelen > 255)
+ return -EINVAL;
+ if (namelen > strnlen(name, 256)) /*maybe only need part of name*/
return -EINVAL;

/* construct the query key description as "[<type>:]<name>" */
@@ -94,10 +96,6 @@ int dns_query(const char *type, const char *name, size_t namelen,
desclen += typelen + 1;
}

- if (!namelen)
- namelen = strnlen(name, 256);
- if (namelen < 3 || namelen > 255)
- return -EINVAL;
desclen += namelen + 1;

desc = kmalloc(desclen, GFP_KERNEL);
--
2.10.1

2018-06-04 18:26:14

by Simon Horman

Subject: Re: [PATCH] net/dns_resolver: dns_query Modify parameter checking to avoid dead code

On Mon, Jun 04, 2018 at 02:40:31PM +0800, nixiaoming wrote:
> After commit 1a4240f4764a ("DNS: Separate out CIFS DNS Resolver code")
> a dead code exists in function dns_query
>
> code show as below:
> if (!name || namelen == 0)
> return -EINVAL;
> /*Now the value of "namelen" cannot be equal to 0*/
> ....
> if (!namelen) /*The condition "!namelen"" cannot be true*/
> namelen = strnlen(name, 256); /*deadcode*/
>
> Modify parameter checking to avoid dead code
>
> Signed-off-by: nixiaoming <[email protected]>
> ---
> net/dns_resolver/dns_query.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c
> index 49da670..f2acee2 100644
> --- a/net/dns_resolver/dns_query.c
> +++ b/net/dns_resolver/dns_query.c
> @@ -81,7 +81,9 @@ int dns_query(const char *type, const char *name, size_t namelen,
> kenter("%s,%*.*s,%zu,%s",
> type, (int)namelen, (int)namelen, name, namelen, options);
>
> - if (!name || namelen == 0)
> + if (!name || namelen < 3 || namelen > 255)
> + return -EINVAL;
> + if (namelen > strnlen(name, 256)) /*maybe only need part of name*/

The line above seems to change the behaviour of this function.
I think it and the previous line can be dropped.

> return -EINVAL;
>
> /* construct the query key description as "[<type>:]<name>" */
> @@ -94,10 +96,6 @@ int dns_query(const char *type, const char *name, size_t namelen,
> desclen += typelen + 1;
> }
>
> - if (!namelen)
> - namelen = strnlen(name, 256);
> - if (namelen < 3 || namelen > 255)
> - return -EINVAL;
> desclen += namelen + 1;

I think the initialisation of desclen can be changed
to include namelen + 1 without changing the behaviour of this function.

>
> desc = kmalloc(desclen, GFP_KERNEL);
> --
> 2.10.1
>