why the skb->lsm_security is NULL inskb_free_security after skb_alloc_security ???

From: Yuan ChunYang (cyyuanml@private)
Date: Tue Sep 23 2003 - 18:12:19 PDT

  • Next message: Yuan ChunYang: "Re: about security_skb_alloc??" 

    HI, now i find a strange problem about skb_alloc_security hook.
  After i allocated security struct for a sk_buff, i find its
skb->lsm_security is NULL when calling skb_free_security hook. I test it
in kernel 2.5.72 with LSM and write codes only two hooks about sk_buff.

  It can not free memory of sk_buff security struct. So my computer is
often halted.  
.
  Can somebody tell me why the skb->lsm_security is NULL in
skb_free_security after skb_alloc_security ???
  Is there some functions in kernel set skb->lsm_security NULL ???
  
  Why hooks about sk_buff is deleter in kernel 2.6???

My codes are followed:
====================================================================
static inline int smos_skb_alloc_security(struct sk_buff * skb, int
gfp_mask)
{
        sk_buff_security_t *sksec;
        int rc = 0;

        sksec = skb->lsm_security;
        if (sksec && sksec->magic == SECOPT_MAGIC) {
                return rc;
        }

        sksec = (sk_buff_security_t *)
kmalloc(sizeof(sk_buff_security_t,GFA_ATOMIC);
        if (!sksec) {
                rc = -ENOMEM;
                return rc;
        }
        memset(sksec, 0, sizeof (sk_buff_security_t));
        sksec->magic = SECOPT_MAGIC;
        sksec->skb = skb;
        skb->lsm_security = sksec;

        printk(KERN_INFO "smos_skb_alloc_security........skb=%p
,skb->lsm_security=%p ..[1-1]\n",skb,skb->lsm_security);
        return rc;
}

static inline void smos_skb_free_security(struct sk_buff * skb)
{
        sk_buff_security_t *ssec = skb->lsm_security;

        printk(KERN_INFO "smos_skb_free_security........skb=%p
,skb->lsm_security=%p ..[2-1]\n",skb,ssec);
        if (!ssec || ssec->magic != SECOPT_MAGIC) return;
        
        skb->lsm_security = NULL;
        kfree(ssec);
        printk(KERN_INFO "smos_skb_free_security........skb=%p ,ssec=%p
...[2-2]\n",skb,ssec);
        return;
}

=========================================================================
DEBUG print info:
kernel: smos_skb_alloc_security........skb=c3305b80
,skb->lsm_security=c2eedea0 ..[1-1]
kernel: smos_skb_free_security........skb=c3305b80
,skb->lsm_security=00000000 ..[2-1]

=========================================================================

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