Re: [RFC 4/8] lsm: smack: smack callbacks for kdbus security hooks

[Casey Schaufler]

On 7/9/2015 3:08 AM, Sergei Zviagintsev wrote:
> Hi,
>
> On Wed, Jul 08, 2015 at 12:25:06PM +0200, Paul Osmialowski wrote:
>> This adds implementation of three smack callbacks sitting behind kdbus
>> security hooks as proposed by Karol Lewandowski.
>>
>> Originates from:
>>
>> git://git.infradead.org/users/pcmoore/selinux (branch: working-kdbus)
>> commit: fc3505d058c001fe72a6f66b833e0be5b2d118f3
>>
>> https://github.com/lmctl/linux.git (branch: kdbus-lsm-v4.for-systemd-v212)
>> commit: 103c26fd27d1ec8c32d85dd3d85681f936ac66fb
>>
>> Signed-off-by: Karol Lewandowski <k.lewandowsk@xxxxxxxxxxx>
>> Signed-off-by: Paul Osmialowski <p.osmialowsk@xxxxxxxxxxx>
>> ---
>>  security/smack/smack_lsm.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 68 insertions(+)
>>
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index a143328..033b756 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -41,6 +41,7 @@
>>  #include <linux/msg.h>
>>  #include <linux/shm.h>
>>  #include <linux/binfmts.h>
>> +#include <kdbus/connection.h>
>>  #include "smack.h"
>>  
>>  #define TRANS_TRUE	"TRUE"
>> @@ -3336,6 +3337,69 @@ static int smack_setprocattr(struct task_struct *p, char *name,
>>  }
>>  
>>  /**
>> + * smack_kdbus_connect - Set the security blob for a KDBus connection
>> + * @conn: the connection
>> + * @secctx: smack label
>> + * @seclen: smack label length
>> + *
>> + * Returns 0
>> + */
>> +static int smack_kdbus_connect(struct kdbus_conn *conn,
>> +			       const char *secctx, u32 seclen)
>> +{
>> +	struct smack_known *skp;
>> +
>> +	if (secctx && seclen > 0)
>> +		skp = smk_import_entry(secctx, seclen);
>> +	else
>> +		skp = smk_of_current();
>> +	conn->security = skp;
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>> + * smack_kdbus_conn_free - Clear the security blob for a KDBus connection
>> + * @conn: the connection
>> + *
>> + * Clears the blob pointer
>> + */
>> +static void smack_kdbus_conn_free(struct kdbus_conn *conn)
>> +{
>> +	conn->security = NULL;
>> +}
>> +
>> +/**
>> + * smack_kdbus_talk - Smack access on KDBus
>> + * @src: source kdbus connection
>> + * @dst: destination kdbus connection
>> + *
>> + * Return 0 if a subject with the smack of sock could access
>> + * an object with the smack of other, otherwise an error code
>> + */
>> +static int smack_kdbus_talk(const struct kdbus_conn *src,
>> +			    const struct kdbus_conn *dst)
>> +{
>> +	struct smk_audit_info ad;
>> +	struct smack_known *sskp = src->security;
>> +	struct smack_known *dskp = dst->security;
>> +	int ret;
>> +
>> +	BUG_ON(sskp == NULL);
>> +	BUG_ON(dskp == NULL);
> I am not familiar with the smack code so far, but I see that current
> security/smack/smack_lsm.c contains only one BUG_ON and this patch adds
> another two.

Smack does not use BUG_ON for routine error checking. If there
is reason to expect that these values will not be set the case
should be checked for and handled. Otherwise, I don't believe
in cluttering the code with assertions.

>
>> +
>> +	if (smack_privileged(CAP_MAC_OVERRIDE))
>> +		return 0;
>> +
>> +	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_NONE);
>> +
>> +	ret = smk_access(sskp, dskp, MAY_WRITE, &ad);
>> +	if (ret)
>> +		return ret;
>> +	return 0;
> Three redundant lines here.
>
>> +}
>> +
>> +/**
>>   * smack_unix_stream_connect - Smack access on UDS
>>   * @sock: one sock
>>   * @other: the other sock
>> @@ -4393,6 +4457,10 @@ struct security_hook_list smack_hooks[] = {
>>  	LSM_HOOK_INIT(inode_notifysecctx, smack_inode_notifysecctx),
>>  	LSM_HOOK_INIT(inode_setsecctx, smack_inode_setsecctx),
>>  	LSM_HOOK_INIT(inode_getsecctx, smack_inode_getsecctx),
>> +
>> +	LSM_HOOK_INIT(kdbus_connect, smack_kdbus_connect),
>> +	LSM_HOOK_INIT(kdbus_conn_free, smack_kdbus_conn_free),
>> +	LSM_HOOK_INIT(kdbus_talk, smack_kdbus_talk),
>>  };
>>  
>>  
>> -- 
>> 1.9.1
>>
>> --
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