Re: Fix for synchronization issue in IPV6 implementation in smack module(v3.18)

[Ahmed S. Darwish]

Hi Vishal,

On Thu, Jan 08, 2015 at 10:11:52PM +0530, Vishal Goel wrote:
>  [PATCH] This patch fixes the synchronization issue in IPv6
>  implementation. Previously there was no synchronization mechanism used while
>  accessing(adding/reading/deletion) smk_ipv6_port_list. It could be possible
>  that when one thread is reading the list, at the same time another thread is
>  adding/deleting in the list.So it is possible that reader thread will read
>  the inaccurate or incomplete list. So to make sure that reader thread will
>  read the accurate list, rcu mechanism has been used while accessing the
>  list.RCU allows readers to access a data structure even when it is in the
>  process of being updated
> 
> Signed-off-by: Vishal Goel <vishal.goel@xxxxxxxxxxx>
>             Himanshu Shukla <himanshu.sh@xxxxxxxxxxx>

The legality of your patches are blurry. You're sending from
a personal email, while having Signed-off-by signatures by your
employer.

You **really** need to add a "From: XXX@xxxxxxxxxxx" header on
the very first line of your emails if this is a sponsored work.
Kindly check Documentation/SubmittingPatches for further details.

Beside the above:

- Your patches are not applicable to the tree since they're
  white-spaces mangled. You're using Gmail's web interface, which
  is well known at converting tabs to white-spaces. Check
  Documentation/email-clients.txt for further details.

- Please fix you Subject line. Make it something in the form of:
  [PATCH 1/3] smack: Fix xxx

- No need for "[PATCH]" in the commit log body, only in the
  subject line.

- Please make the commit message more comprehensible. Check
  the kernel git log history for good examples. A grammar
  check will also be nice; there are a number of free good
  tools on the web.

- Add "Signed-off-by" headers for each developer. In the patch
  above, you'll need _two_ "Signed-off-by" lines.

- You're sending multiple related patches, but posting each one
  in its own thread. This will make it very very hard for review,
  especially in a very busy list like LKML. Please send related
  patches in an "email thread", with clear sequence numbers.

  (e.g., your follow-up patch titled as "In Ref to previous 3
  patches:Fix for synchronization..." is completely bogus.)

Happy kernel coding :-)

Regards,
Darwish

> ---
>  security/smack/smack_lsm.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index d515ec2..b3427ee 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -52,6 +52,7 @@
>  #define SMK_RECEIVING  1
>  #define SMK_SENDING    2
> 
> +DEFINE_MUTEX(smack_ipv6_lock);
>  LIST_HEAD(smk_ipv6_port_list);
> 
>  #ifdef CONFIG_SECURITY_SMACK_BRINGUP
> @@ -2232,17 +2233,20 @@ static void smk_ipv6_port_label(struct socket
> *sock, struct sockaddr *address)
>              * on the bound socket. Take the changes to the port
>              * as well.
>              */
> -           list_for_each_entry(spp, &smk_ipv6_port_list, list) {
> +           rcu_read_lock();
> +           list_for_each_entry_rcu(spp, &smk_ipv6_port_list, list) {
>                   if (sk != spp->smk_sock)
>                         continue;
>                   spp->smk_in = ssp->smk_in;
>                   spp->smk_out = ssp->smk_out;
> +                 rcu_read_unlock();
>                   return;
>             }
>             /*
>              * A NULL address is only used for updating existing
>              * bound entries. If there isn't one, it's OK.
>              */
> +           rcu_read_unlock();
>             return;
>       }
> 
> @@ -2258,16 +2262,18 @@ static void smk_ipv6_port_label(struct socket
> *sock, struct sockaddr *address)
>        * Look for an existing port list entry.
>        * This is an indication that a port is getting reused.
>        */
> -     list_for_each_entry(spp, &smk_ipv6_port_list, list) {
> +     rcu_read_lock();
> +     list_for_each_entry_rcu(spp, &smk_ipv6_port_list, list) {
>             if (spp->smk_port != port)
>                   continue;
>             spp->smk_port = port;
>             spp->smk_sock = sk;
>             spp->smk_in = ssp->smk_in;
>             spp->smk_out = ssp->smk_out;
> +           rcu_read_unlock();
>             return;
>       }
> -
> +     rcu_read_unlock();
>       /*
>        * A new port entry is required.
>        */
> @@ -2280,7 +2286,9 @@ static void smk_ipv6_port_label(struct socket
> *sock, struct sockaddr *address)
>       spp->smk_in = ssp->smk_in;
>       spp->smk_out = ssp->smk_out;
> 
> -     list_add(&spp->list, &smk_ipv6_port_list);
> +     mutex_lock(&smack_ipv6_lock);
> +     list_add_rcu(&spp->list, &smk_ipv6_port_list);
> +     mutex_unlock(&smack_ipv6_lock);
>       return;
>  }
> 
> @@ -2335,8 +2343,8 @@ static int smk_ipv6_port_check(struct sock *sk,
> struct sockaddr_in6 *address,
>             skp = &smack_known_web;
>             goto auditout;
>       }
> -
> -     list_for_each_entry(spp, &smk_ipv6_port_list, list) {
> +     rcu_read_lock();
> +     list_for_each_entry_rcu(spp, &smk_ipv6_port_list, list) {
>             if (spp->smk_port != port)
>                   continue;
>             object = spp->smk_in;
> @@ -2344,6 +2352,7 @@ static int smk_ipv6_port_check(struct sock *sk,
> struct sockaddr_in6 *address,
>                   ssp->smk_packet = spp->smk_out;
>             break;
>       }
> +     rcu_read_unlock();
> 
>  auditout:
> 
> --
> 1.8.3.2
> --
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