kernel module crashing on reading sock information

**pkolakkar** · 04-06-2011

Hey guys,

Ive been writing a kernel module to print per socket per process tcp stats using tcp_get_info function. The issue is i can get until the sock structure...but later due to probably locking issues I am unable to get the module fully functional. It runs for about 10 minutes and then crashes off....Any help would be highly appreciated.

The function code is pasted below.

int process_tcpInfo(struct seq_file *s, struct task_struct *task){
struct file *fArray;
struct files_struct * files;
struct dentry *dPointer;
struct inode *iPointer;
struct socket *stPointer;
struct sock *skPointer;
//struct tcp_info* tiTcpInfo;
struct inet_sock *inSock;
u16 dport;
u16 sport;
u32 daddr;
u32 recvaddr;
int wscale;
int sack;
unsigned int hash;
struct inet_ehash_bucket *head;
struct fdtable *fdt=NULL;
struct tcp_info *tiTcpInfo;
unsigned long flags;
unsigned long readflags;
int i=0;
u8 rcv_wscale=0;
u8 snd_wscale=0;
tiTcpInfo=kmalloc(sizeof(struct tcp_info), GFP_KERNEL);
if (!tiTcpInfo ){ // fatal kernel allocation error
return -1;
}
if(task){
get_task_struct(task);
}

files=get_files_struct(task);
if(!files){
put_task_struct(task);
return 0;
}

//filp=fcheck_files(files, fd);

if(files){
//printk(KERN_INFO "seqtcpmod: reached line %d\n", __LINE__);
fdt = files_fdtable(files);
//printk(KERN_INFO "seqtcpmod: reached line %d\n", __LINE__);
}
if(fdt==NULL){
//printk(KERN_INFO "seqtcpmod: reached line %d\n", __LINE__);
put_files_struct(files);
put_task_struct(task);
return 0;
}

for(i=0;imax_fds;i++){
spin_lock_irqsave(&files->file_lock, flags);
fArray=rcu_dereference(fdt->fd[i]);
if(!fArray){
spin_unlock_irqrestore(&files->file_lock,flags);
break;
}
get_file(fArray);
dPointer = rcu_dereference(fArray->f_dentry);
if(dPointer == NULL){
spin_unlock_irqrestore(&files->file_lock,flags);
fput(fArray);
continue;
}
dPointer=dget(dPointer);
iPointer = rcu_dereference(dPointer->d_inode);
if(iPointer == NULL){
spin_unlock_irqrestore(&files->file_lock,flags);
put(dPointer);
fput(fArray);
continue;
}
igrab(iPointer);
stPointer=rcu_dereference(SOCKET_I(iPointer));
if(stPointer==NULL){
spin_unlock_irqrestore(&files->file_lock,flags);
iput(iPointer);
dput(dPointer);
fput(fArray);
continue;
}
skPointer=rcu_dereference(stPointer->sk);
if(skPointer == NULL){
spin_unlock_irqrestore(&files->file_lock,flags);
iput(SOCK_INODE(stPointer));
dput(dPointer);
fput(fArray);
continue;
}
spin_unlock_irqrestore(&files->file_lock,flags);
iput(SOCK_INODE(stPointer));
dput(dPointer);
fput(fArray);

// PROBLEM CAUSING IF BLOCK

if((stPointer->type == 1)&&((skPointer->sk_family==PF_INET)||(skPointer->sk_family==PF_INET6)||(skPointer->sk_family==AF_INET)||(skPointer->sk_family==AF_INET6))&& (skPointer)){

local_bh_disable();
head = inet_ehash_bucket(&tcp_hashinfo, hash);
read_lock_irqsave(&head->lock,readflags);
inSock=inet_sk(skPointer);
dport=ntohs(inSock->dport);
sport=ntohs(inSock->sport);
daddr=ntohl(inSock->daddr);
recvaddr=ntohl(inSock->rcv_saddr);
tcp_get_info(skPointer, tiTcpInfo);
read_unlock_irqrestore(&head->lock,readflags);
local_bh_enable();
if((tiTcpInfo->tcpi_options & TCPI_OPT_WSCALE )== TCPI_OPT_WSCALE){
wscale=1;
}else{
wscale=0;
}
if((tiTcpInfo->tcpi_options & TCPI_OPT_SACK )== TCPI_OPT_SACK){
sack=1;
}else{
sack=0;
}
rcv_wscale|=tiTcpInfo->tcpi_rcv_wscale;
snd_wscale|=tiTcpInfo->tcpi_snd_wscale;
if(tiTcpInfo!=NULL){
seq_printf(s,"%d %s %d %d %d %u:%hu %u:%hu %hd %hd %hd %hd %hd %hd %hd %hd %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u\n",task->pid, task->comm, i, wscale,sack,recvaddr,sport,daddr,dport, tiTcpInfo->tcpi_state, tiTcpInfo->tcpi_ca_state, tiTcpInfo->tcpi_retransmits, tiTcpInfo->tcpi_probes, tiTcpInfo->tcpi_backoff, tiTcpInfo->tcpi_options, snd_wscale, rcv_wscale, tiTcpInfo->tcpi_rto, tiTcpInfo->tcpi_ato, tiTcpInfo->tcpi_snd_mss, tiTcpInfo->tcpi_rcv_mss, tiTcpInfo->tcpi_unacked, tiTcpInfo->tcpi_sacked, tiTcpInfo->tcpi_lost, tiTcpInfo->tcpi_retrans, tiTcpInfo->tcpi_fackets, tiTcpInfo->tcpi_last_data_sent, tiTcpInfo->tcpi_last_ack_sent, tiTcpInfo->tcpi_last_data_recv, tiTcpInfo->tcpi_last_ack_recv, tiTcpInfo->tcpi_pmtu, tiTcpInfo->tcpi_rcv_ssthresh, tiTcpInfo->tcpi_rtt, tiTcpInfo->tcpi_rttvar, tiTcpInfo->tcpi_snd_ssthresh, tiTcpInfo->tcpi_snd_cwnd, tiTcpInfo->tcpi_advmss, tiTcpInfo->tcpi_reordering, tiTcpInfo->tcpi_rcv_rtt, tiTcpInfo->tcpi_rcv_space, tiTcpInfo->tcpi_total_retrans);
}

}

} // FOR LOOP ENDS HERE

put_files_struct(files);
put_task_struct(task);
kfree(tiTcpInfo);
return 1;
}

**Rubberman** · 04-06-2011

PLEASE put your code inside code blocks, otherwise it is effectively impossible to read. Example:

Code:

/* This is a comment */
int function(void)
{
    /* This is inside a function */
    for (int i = 0; i < 10; i++)
    {
        /* this is inside a loop */
    }
}

**pkolakkar** · 04-06-2011

Apologize for the inconvenience caused due to incorrect formatting. I hope the one below is fine. Still stuck at this. Thanks for your reponse.

Code:


int process_tcpInfo(struct seq_file *s, struct task_struct *task){ 
struct file *fArray; 
struct files_struct * files; 
struct dentry *dPointer; 
struct inode *iPointer; 
struct socket *stPointer; 
struct sock *skPointer; 
//struct tcp_info* tiTcpInfo; 
struct inet_sock *inSock; 
u16 dport; 
u16 sport; 
u32 daddr; 
u32 recvaddr; 
int wscale; 
int sack; 
unsigned int hash; 
struct inet_ehash_bucket *head; 
struct fdtable *fdt=NULL; 
struct tcp_info *tiTcpInfo; 
unsigned long flags; 
unsigned long readflags; 
int i=0; 
u8 rcv_wscale=0; 
u8 snd_wscale=0; 
tiTcpInfo=kmalloc(sizeof(struct tcp_info), GFP_KERNEL); 
if (!tiTcpInfo ){ // fatal kernel allocation error 
               return -1; 
} 
if(task){ 
               get_task_struct(task); 
} 

files=get_files_struct(task); 
if(!files){ 
            put_task_struct(task); 
            return 0; 
} 

if(files){ 
              fdt = files_fdtable(files); 
} 
if(fdt==NULL){ 
              put_files_struct(files); 
              put_task_struct(task); 
              return 0; 
} 

for(i=0;imax_fds;i++){ 
               spin_lock_irqsave(&files->file_lock, flags); 
               fArray=rcu_dereference(fdt->fd[i]); 
               if(!fArray){ 
                      spin_unlock_irqrestore(&files->file_lock,flags); 
                      break; 
                } 
                get_file(fArray); 
                dPointer = rcu_dereference(fArray->f_dentry); 
                if(dPointer == NULL){ 
                         spin_unlock_irqrestore(&files->file_lock,flags); 
                         fput(fArray); 
                         continue; 
                } 
                dPointer=dget(dPointer); 
                iPointer = rcu_dereference(dPointer->d_inode); 
                if(iPointer == NULL){ 
                          spin_unlock_irqrestore(&files->file_lock,flags); 
                          put(dPointer); 
                          fput(fArray); 
                          continue; 
                } 
                igrab(iPointer); 
                stPointer=rcu_dereference(SOCKET_I(iPointer)); 
                if(stPointer==NULL){ 
                          spin_unlock_irqrestore(&files->file_lock,flags); 
                          iput(iPointer); 
                          dput(dPointer); 
                          fput(fArray); 
                          continue; 
                 } 
                 skPointer=rcu_dereference(stPointer->sk); 
                 if(skPointer == NULL){ 
                          spin_unlock_irqrestore(&files->file_lock,flags); 
                          iput(SOCK_INODE(stPointer)); 
                          dput(dPointer); 
                          fput(fArray); 
                          continue; 
                  } 
                 spin_unlock_irqrestore(&files->file_lock,flags); 
                 iput(SOCK_INODE(stPointer)); 
                 dput(dPointer); 
                 fput(fArray); 

// PROBLEM CAUSING IF BLOCK 
                 if((stPointer->type == 1)&&((skPointer->sk_family==PF_INET)||(skPointer->sk_family==PF_INET6)||(skPointer->sk_family==AF_INET)||(skPointer->sk_family==AF_INET6))&& (skPointer)){ 
                                  local_bh_disable(); 
                                  head = inet_ehash_bucket(&tcp_hashinfo, hash); 
                                  read_lock_irqsave(&head->lock,readflags); 
                                  inSock=inet_sk(skPointer); 
                                  dport=ntohs(inSock->dport); 
                                  sport=ntohs(inSock->sport); 
                                  daddr=ntohl(inSock->daddr); 
                                  recvaddr=ntohl(inSock->rcv_saddr); 
                                  tcp_get_info(skPointer, tiTcpInfo); 
                                  read_unlock_irqrestore(&head->lock,readflags); 
                                  local_bh_enable(); 
                                  if((tiTcpInfo->tcpi_options & TCPI_OPT_WSCALE )== TCPI_OPT_WSCALE){ 
                                                   wscale=1; 
                                    }else{ 
                                                   wscale=0; 
                                  } 
                                  if((tiTcpInfo->tcpi_options & TCPI_OPT_SACK )== TCPI_OPT_SACK){ 
                                                   sack=1; 
                                  }else{ 
                                                   sack=0; 
                                  } 
                                  rcv_wscale|=tiTcpInfo->tcpi_rcv_wscale; 
                                  snd_wscale|=tiTcpInfo->tcpi_snd_wscale; 
                                  if(tiTcpInfo!=NULL){ 
                                                        seq_printf(s,"%d %s %d %d %d %u:%hu %u:%hu %hd %hd %hd %hd %hd %hd %hd %hd %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u %u\n",task->pid, task->comm, i, wscale,sack,recvaddr,sport,daddr,dport, tiTcpInfo->tcpi_state, tiTcpInfo->tcpi_ca_state, tiTcpInfo->tcpi_retransmits, tiTcpInfo->tcpi_probes, tiTcpInfo->tcpi_backoff, tiTcpInfo->tcpi_options, snd_wscale, rcv_wscale, tiTcpInfo->tcpi_rto, tiTcpInfo->tcpi_ato, tiTcpInfo->tcpi_snd_mss, tiTcpInfo->tcpi_rcv_mss, tiTcpInfo->tcpi_unacked, tiTcpInfo->tcpi_sacked, tiTcpInfo->tcpi_lost, tiTcpInfo->tcpi_retrans, tiTcpInfo->tcpi_fackets, tiTcpInfo->tcpi_last_data_sent, tiTcpInfo->tcpi_last_ack_sent, tiTcpInfo->tcpi_last_data_recv, tiTcpInfo->tcpi_last_ack_recv, tiTcpInfo->tcpi_pmtu, tiTcpInfo->tcpi_rcv_ssthresh, tiTcpInfo->tcpi_rtt, tiTcpInfo->tcpi_rttvar, tiTcpInfo->tcpi_snd_ssthresh, tiTcpInfo->tcpi_snd_cwnd, tiTcpInfo->tcpi_advmss, tiTcpInfo->tcpi_reordering, tiTcpInfo->tcpi_rcv_rtt, tiTcpInfo->tcpi_rcv_space, tiTcpInfo->tcpi_total_retrans); 
                                         }                  

                 } 
     } // FOR LOOP ENDS HERE 

   put_files_struct(files); 
   put_task_struct(task); 
   kfree(tiTcpInfo); 
   return 1; 
}

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