system/linux
system/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux synced 2024-11-05 18:23:50 +00:00
Code Issues Projects Releases Packages Wiki Activity
linux/net/rds/recv.c
Weiping Pan 06b6a1cf6e rds: set correct msg_namelen 
Jay Fenlason (fenlason@redhat.com) found a bug,
that recvfrom() on an RDS socket can return the contents of random kernel
memory to userspace if it was called with a address length larger than
sizeof(struct sockaddr_in).
rds_recvmsg() also fails to set the addr_len paramater properly before
returning, but that's just a bug.
There are also a number of cases wher recvfrom() can return an entirely bogus
address. Anything in rds_recvmsg() that returns a non-negative value but does
not go through the "sin = (struct sockaddr_in *)msg->msg_name;" code path
at the end of the while(1) loop will return up to 128 bytes of kernel memory
to userspace.

And I write two test programs to reproduce this bug, you will see that in
rds_server, fromAddr will be overwritten and the following sock_fd will be
destroyed.
Yes, it is the programmer's fault to set msg_namelen incorrectly, but it is
better to make the kernel copy the real length of address to user space in
such case.

How to run the test programs ?
I test them on 32bit x86 system, 3.5.0-rc7.

1 compile
gcc -o rds_client rds_client.c
gcc -o rds_server rds_server.c

2 run ./rds_server on one console

3 run ./rds_client on another console

4 you will see something like:
server is waiting to receive data...
old socket fd=3
server received data from client:data from client
msg.msg_namelen=32
new socket fd=-1067277685
sendmsg()
: Bad file descriptor

/***************** rds_client.c ********************/

int main(void)
{
	int sock_fd;
	struct sockaddr_in serverAddr;
	struct sockaddr_in toAddr;
	char recvBuffer[128] = "data from client";
	struct msghdr msg;
	struct iovec iov;

	sock_fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
	if (sock_fd < 0) {
		perror("create socket error\n");
		exit(1);
	}

	memset(&serverAddr, 0, sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	serverAddr.sin_port = htons(4001);

	if (bind(sock_fd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) {
		perror("bind() error\n");
		close(sock_fd);
		exit(1);
	}

	memset(&toAddr, 0, sizeof(toAddr));
	toAddr.sin_family = AF_INET;
	toAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	toAddr.sin_port = htons(4000);
	msg.msg_name = &toAddr;
	msg.msg_namelen = sizeof(toAddr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = strlen(recvBuffer) + 1;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;

	if (sendmsg(sock_fd, &msg, 0) == -1) {
		perror("sendto() error\n");
		close(sock_fd);
		exit(1);
	}

	printf("client send data:%s\n", recvBuffer);

	memset(recvBuffer, '\0', 128);

	msg.msg_name = &toAddr;
	msg.msg_namelen = sizeof(toAddr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = 128;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;
	if (recvmsg(sock_fd, &msg, 0) == -1) {
		perror("recvmsg() error\n");
		close(sock_fd);
		exit(1);
	}

	printf("receive data from server:%s\n", recvBuffer);

	close(sock_fd);

	return 0;
}

/***************** rds_server.c ********************/

int main(void)
{
	struct sockaddr_in fromAddr;
	int sock_fd;
	struct sockaddr_in serverAddr;
	unsigned int addrLen;
	char recvBuffer[128];
	struct msghdr msg;
	struct iovec iov;

	sock_fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
	if(sock_fd < 0) {
		perror("create socket error\n");
		exit(0);
	}

	memset(&serverAddr, 0, sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	serverAddr.sin_port = htons(4000);
	if (bind(sock_fd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) {
		perror("bind error\n");
		close(sock_fd);
		exit(1);
	}

	printf("server is waiting to receive data...\n");
	msg.msg_name = &fromAddr;

	/*
	 * I add 16 to sizeof(fromAddr), ie 32,
	 * and pay attention to the definition of fromAddr,
	 * recvmsg() will overwrite sock_fd,
	 * since kernel will copy 32 bytes to userspace.
	 *
	 * If you just use sizeof(fromAddr), it works fine.
	 * */
	msg.msg_namelen = sizeof(fromAddr) + 16;
	/* msg.msg_namelen = sizeof(fromAddr); */
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = 128;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;

	while (1) {
		printf("old socket fd=%d\n", sock_fd);
		if (recvmsg(sock_fd, &msg, 0) == -1) {
			perror("recvmsg() error\n");
			close(sock_fd);
			exit(1);
		}
		printf("server received data from client:%s\n", recvBuffer);
		printf("msg.msg_namelen=%d\n", msg.msg_namelen);
		printf("new socket fd=%d\n", sock_fd);
		strcat(recvBuffer, "--data from server");
		if (sendmsg(sock_fd, &msg, 0) == -1) {
			perror("sendmsg()\n");
			close(sock_fd);
			exit(1);
		}
	}

	close(sock_fd);
	return 0;
}

Signed-off-by: Weiping Pan <wpan@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2012-07-23 01:01:44 -07:00

550 lines
15 KiB
C
Raw Blame History

/*
* Copyright (c) 2006 Oracle. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*
*/
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/in.h>
#include <linux/export.h>
#include "rds.h"
void rds_inc_init(struct rds_incoming *inc, struct rds_connection *conn,
__be32 saddr)
{
atomic_set(&inc->i_refcount, 1);
INIT_LIST_HEAD(&inc->i_item);
inc->i_conn = conn;
inc->i_saddr = saddr;
inc->i_rdma_cookie = 0;
}
EXPORT_SYMBOL_GPL(rds_inc_init);
static void rds_inc_addref(struct rds_incoming *inc)
{
rdsdebug("addref inc %p ref %d\n", inc, atomic_read(&inc->i_refcount));
atomic_inc(&inc->i_refcount);
}
void rds_inc_put(struct rds_incoming *inc)
{
rdsdebug("put inc %p ref %d\n", inc, atomic_read(&inc->i_refcount));
if (atomic_dec_and_test(&inc->i_refcount)) {
BUG_ON(!list_empty(&inc->i_item));
inc->i_conn->c_trans->inc_free(inc);
}
}
EXPORT_SYMBOL_GPL(rds_inc_put);
static void rds_recv_rcvbuf_delta(struct rds_sock *rs, struct sock *sk,
struct rds_cong_map *map,
int delta, __be16 port)
{
int now_congested;
if (delta == 0)
return;
rs->rs_rcv_bytes += delta;
now_congested = rs->rs_rcv_bytes > rds_sk_rcvbuf(rs);
rdsdebug("rs %p (%pI4:%u) recv bytes %d buf %d "
"now_cong %d delta %d\n",
rs, &rs->rs_bound_addr,
ntohs(rs->rs_bound_port), rs->rs_rcv_bytes,
rds_sk_rcvbuf(rs), now_congested, delta);
/* wasn't -> am congested */
if (!rs->rs_congested && now_congested) {
rs->rs_congested = 1;
rds_cong_set_bit(map, port);
rds_cong_queue_updates(map);
}
/* was -> aren't congested */
/* Require more free space before reporting uncongested to prevent
bouncing cong/uncong state too often */
else if (rs->rs_congested && (rs->rs_rcv_bytes < (rds_sk_rcvbuf(rs)/2))) {
rs->rs_congested = 0;
rds_cong_clear_bit(map, port);
rds_cong_queue_updates(map);
}
/* do nothing if no change in cong state */
}
/*
* Process all extension headers that come with this message.
*/
static void rds_recv_incoming_exthdrs(struct rds_incoming *inc, struct rds_sock *rs)
{
struct rds_header *hdr = &inc->i_hdr;
unsigned int pos = 0, type, len;
union {
struct rds_ext_header_version version;
struct rds_ext_header_rdma rdma;
struct rds_ext_header_rdma_dest rdma_dest;
} buffer;
while (1) {
len = sizeof(buffer);
type = rds_message_next_extension(hdr, &pos, &buffer, &len);
if (type == RDS_EXTHDR_NONE)
break;
/* Process extension header here */
switch (type) {
case RDS_EXTHDR_RDMA:
rds_rdma_unuse(rs, be32_to_cpu(buffer.rdma.h_rdma_rkey), 0);
break;
case RDS_EXTHDR_RDMA_DEST:
/* We ignore the size for now. We could stash it
* somewhere and use it for error checking. */
inc->i_rdma_cookie = rds_rdma_make_cookie(
be32_to_cpu(buffer.rdma_dest.h_rdma_rkey),
be32_to_cpu(buffer.rdma_dest.h_rdma_offset));
break;
}
}
}
/*
* The transport must make sure that this is serialized against other
* rx and conn reset on this specific conn.
*
* We currently assert that only one fragmented message will be sent
* down a connection at a time. This lets us reassemble in the conn
* instead of per-flow which means that we don't have to go digging through
* flows to tear down partial reassembly progress on conn failure and
* we save flow lookup and locking for each frag arrival. It does mean
* that small messages will wait behind large ones. Fragmenting at all
* is only to reduce the memory consumption of pre-posted buffers.
*
* The caller passes in saddr and daddr instead of us getting it from the
* conn. This lets loopback, who only has one conn for both directions,
* tell us which roles the addrs in the conn are playing for this message.
*/
void rds_recv_incoming(struct rds_connection *conn, __be32 saddr, __be32 daddr,
struct rds_incoming *inc, gfp_t gfp)
{
struct rds_sock *rs = NULL;
struct sock *sk;
unsigned long flags;
inc->i_conn = conn;
inc->i_rx_jiffies = jiffies;
rdsdebug("conn %p next %llu inc %p seq %llu len %u sport %u dport %u "
"flags 0x%x rx_jiffies %lu\n", conn,
(unsigned long long)conn->c_next_rx_seq,
inc,
(unsigned long long)be64_to_cpu(inc->i_hdr.h_sequence),
be32_to_cpu(inc->i_hdr.h_len),
be16_to_cpu(inc->i_hdr.h_sport),
be16_to_cpu(inc->i_hdr.h_dport),
inc->i_hdr.h_flags,
inc->i_rx_jiffies);
/*
* Sequence numbers should only increase. Messages get their
* sequence number as they're queued in a sending conn. They
* can be dropped, though, if the sending socket is closed before
* they hit the wire. So sequence numbers can skip forward
* under normal operation. They can also drop back in the conn
* failover case as previously sent messages are resent down the
* new instance of a conn. We drop those, otherwise we have
* to assume that the next valid seq does not come after a
* hole in the fragment stream.
*
* The headers don't give us a way to realize if fragments of
* a message have been dropped. We assume that frags that arrive
* to a flow are part of the current message on the flow that is
* being reassembled. This means that senders can't drop messages
* from the sending conn until all their frags are sent.
*
* XXX we could spend more on the wire to get more robust failure
* detection, arguably worth it to avoid data corruption.
*/
if (be64_to_cpu(inc->i_hdr.h_sequence) < conn->c_next_rx_seq &&
(inc->i_hdr.h_flags & RDS_FLAG_RETRANSMITTED)) {
rds_stats_inc(s_recv_drop_old_seq);
goto out;
}
conn->c_next_rx_seq = be64_to_cpu(inc->i_hdr.h_sequence) + 1;
if (rds_sysctl_ping_enable && inc->i_hdr.h_dport == 0) {
rds_stats_inc(s_recv_ping);
rds_send_pong(conn, inc->i_hdr.h_sport);
goto out;
}
rs = rds_find_bound(daddr, inc->i_hdr.h_dport);
if (!rs) {
rds_stats_inc(s_recv_drop_no_sock);
goto out;
}
/* Process extension headers */
rds_recv_incoming_exthdrs(inc, rs);
/* We can be racing with rds_release() which marks the socket dead. */
sk = rds_rs_to_sk(rs);
/* serialize with rds_release -> sock_orphan */
write_lock_irqsave(&rs->rs_recv_lock, flags);
if (!sock_flag(sk, SOCK_DEAD)) {
rdsdebug("adding inc %p to rs %p's recv queue\n", inc, rs);
rds_stats_inc(s_recv_queued);
rds_recv_rcvbuf_delta(rs, sk, inc->i_conn->c_lcong,
be32_to_cpu(inc->i_hdr.h_len),
inc->i_hdr.h_dport);
rds_inc_addref(inc);
list_add_tail(&inc->i_item, &rs->rs_recv_queue);
__rds_wake_sk_sleep(sk);
} else {
rds_stats_inc(s_recv_drop_dead_sock);
}
write_unlock_irqrestore(&rs->rs_recv_lock, flags);
out:
if (rs)
rds_sock_put(rs);
}
EXPORT_SYMBOL_GPL(rds_recv_incoming);
/*
* be very careful here. This is being called as the condition in
* wait_event_*() needs to cope with being called many times.
*/
static int rds_next_incoming(struct rds_sock *rs, struct rds_incoming **inc)
{
unsigned long flags;
if (!*inc) {
read_lock_irqsave(&rs->rs_recv_lock, flags);
if (!list_empty(&rs->rs_recv_queue)) {
*inc = list_entry(rs->rs_recv_queue.next,
struct rds_incoming,
i_item);
rds_inc_addref(*inc);
}
read_unlock_irqrestore(&rs->rs_recv_lock, flags);
}
return *inc != NULL;
}
static int rds_still_queued(struct rds_sock *rs, struct rds_incoming *inc,
int drop)
{
struct sock *sk = rds_rs_to_sk(rs);
int ret = 0;
unsigned long flags;
write_lock_irqsave(&rs->rs_recv_lock, flags);
if (!list_empty(&inc->i_item)) {
ret = 1;
if (drop) {
/* XXX make sure this i_conn is reliable */
rds_recv_rcvbuf_delta(rs, sk, inc->i_conn->c_lcong,
-be32_to_cpu(inc->i_hdr.h_len),
inc->i_hdr.h_dport);
list_del_init(&inc->i_item);
rds_inc_put(inc);
}
}
write_unlock_irqrestore(&rs->rs_recv_lock, flags);
rdsdebug("inc %p rs %p still %d dropped %d\n", inc, rs, ret, drop);
return ret;
}
/*
* Pull errors off the error queue.
* If msghdr is NULL, we will just purge the error queue.
*/
int rds_notify_queue_get(struct rds_sock *rs, struct msghdr *msghdr)
{
struct rds_notifier *notifier;
struct rds_rdma_notify cmsg = { 0 }; /* fill holes with zero */
unsigned int count = 0, max_messages = ~0U;
unsigned long flags;
LIST_HEAD(copy);
int err = 0;
/* put_cmsg copies to user space and thus may sleep. We can't do this
* with rs_lock held, so first grab as many notifications as we can stuff
* in the user provided cmsg buffer. We don't try to copy more, to avoid
* losing notifications - except when the buffer is so small that it wouldn't
* even hold a single notification. Then we give him as much of this single
* msg as we can squeeze in, and set MSG_CTRUNC.
*/
if (msghdr) {
max_messages = msghdr->msg_controllen / CMSG_SPACE(sizeof(cmsg));
if (!max_messages)
max_messages = 1;
}
spin_lock_irqsave(&rs->rs_lock, flags);
while (!list_empty(&rs->rs_notify_queue) && count < max_messages) {
notifier = list_entry(rs->rs_notify_queue.next,
struct rds_notifier, n_list);
list_move(&notifier->n_list, &copy);
count++;
}
spin_unlock_irqrestore(&rs->rs_lock, flags);
if (!count)
return 0;
while (!list_empty(&copy)) {
notifier = list_entry(copy.next, struct rds_notifier, n_list);
if (msghdr) {
cmsg.user_token = notifier->n_user_token;
cmsg.status = notifier->n_status;
err = put_cmsg(msghdr, SOL_RDS, RDS_CMSG_RDMA_STATUS,
sizeof(cmsg), &cmsg);
if (err)
break;
}
list_del_init(&notifier->n_list);
kfree(notifier);
}
/* If we bailed out because of an error in put_cmsg,
* we may be left with one or more notifications that we
* didn't process. Return them to the head of the list. */
if (!list_empty(&copy)) {
spin_lock_irqsave(&rs->rs_lock, flags);
list_splice(&copy, &rs->rs_notify_queue);
spin_unlock_irqrestore(&rs->rs_lock, flags);
}
return err;
}
/*
* Queue a congestion notification
*/
static int rds_notify_cong(struct rds_sock *rs, struct msghdr *msghdr)
{
uint64_t notify = rs->rs_cong_notify;
unsigned long flags;
int err;
err = put_cmsg(msghdr, SOL_RDS, RDS_CMSG_CONG_UPDATE,
sizeof(notify), &notify);
if (err)
return err;
spin_lock_irqsave(&rs->rs_lock, flags);
rs->rs_cong_notify &= ~notify;
spin_unlock_irqrestore(&rs->rs_lock, flags);
return 0;
}
/*
* Receive any control messages.
*/
static int rds_cmsg_recv(struct rds_incoming *inc, struct msghdr *msg)
{
int ret = 0;
if (inc->i_rdma_cookie) {
ret = put_cmsg(msg, SOL_RDS, RDS_CMSG_RDMA_DEST,
sizeof(inc->i_rdma_cookie), &inc->i_rdma_cookie);
if (ret)
return ret;
}
return 0;
}
int rds_recvmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
size_t size, int msg_flags)
{
struct sock *sk = sock->sk;
struct rds_sock *rs = rds_sk_to_rs(sk);
long timeo;
int ret = 0, nonblock = msg_flags & MSG_DONTWAIT;
struct sockaddr_in *sin;
struct rds_incoming *inc = NULL;
/* udp_recvmsg()->sock_recvtimeo() gets away without locking too.. */
timeo = sock_rcvtimeo(sk, nonblock);
rdsdebug("size %zu flags 0x%x timeo %ld\n", size, msg_flags, timeo);
msg->msg_namelen = 0;
if (msg_flags & MSG_OOB)
goto out;
while (1) {
/* If there are pending notifications, do those - and nothing else */
if (!list_empty(&rs->rs_notify_queue)) {
ret = rds_notify_queue_get(rs, msg);
break;
}
if (rs->rs_cong_notify) {
ret = rds_notify_cong(rs, msg);
break;
}
if (!rds_next_incoming(rs, &inc)) {
if (nonblock) {
ret = -EAGAIN;
break;
}
timeo = wait_event_interruptible_timeout(*sk_sleep(sk),
(!list_empty(&rs->rs_notify_queue) ||
rs->rs_cong_notify ||
rds_next_incoming(rs, &inc)), timeo);
rdsdebug("recvmsg woke inc %p timeo %ld\n", inc,
timeo);
if (timeo > 0 || timeo == MAX_SCHEDULE_TIMEOUT)
continue;
ret = timeo;
if (ret == 0)
ret = -ETIMEDOUT;
break;
}
rdsdebug("copying inc %p from %pI4:%u to user\n", inc,
&inc->i_conn->c_faddr,
ntohs(inc->i_hdr.h_sport));
ret = inc->i_conn->c_trans->inc_copy_to_user(inc, msg->msg_iov,
size);
if (ret < 0)
break;
/*
* if the message we just copied isn't at the head of the
* recv queue then someone else raced us to return it, try
* to get the next message.
*/
if (!rds_still_queued(rs, inc, !(msg_flags & MSG_PEEK))) {
rds_inc_put(inc);
inc = NULL;
rds_stats_inc(s_recv_deliver_raced);
continue;
}
if (ret < be32_to_cpu(inc->i_hdr.h_len)) {
if (msg_flags & MSG_TRUNC)
ret = be32_to_cpu(inc->i_hdr.h_len);
msg->msg_flags |= MSG_TRUNC;
}
if (rds_cmsg_recv(inc, msg)) {
ret = -EFAULT;
goto out;
}
rds_stats_inc(s_recv_delivered);
sin = (struct sockaddr_in *)msg->msg_name;
if (sin) {
sin->sin_family = AF_INET;
sin->sin_port = inc->i_hdr.h_sport;
sin->sin_addr.s_addr = inc->i_saddr;
memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
msg->msg_namelen = sizeof(*sin);
}
break;
}
if (inc)
rds_inc_put(inc);
out:
return ret;
}
/*
* The socket is being shut down and we're asked to drop messages that were
* queued for recvmsg. The caller has unbound the socket so the receive path
* won't queue any more incoming fragments or messages on the socket.
*/
void rds_clear_recv_queue(struct rds_sock *rs)
{
struct sock *sk = rds_rs_to_sk(rs);
struct rds_incoming *inc, *tmp;
unsigned long flags;
write_lock_irqsave(&rs->rs_recv_lock, flags);
list_for_each_entry_safe(inc, tmp, &rs->rs_recv_queue, i_item) {
rds_recv_rcvbuf_delta(rs, sk, inc->i_conn->c_lcong,
-be32_to_cpu(inc->i_hdr.h_len),
inc->i_hdr.h_dport);
list_del_init(&inc->i_item);
rds_inc_put(inc);
}
write_unlock_irqrestore(&rs->rs_recv_lock, flags);
}
/*
* inc->i_saddr isn't used here because it is only set in the receive
* path.
*/
void rds_inc_info_copy(struct rds_incoming *inc,
struct rds_info_iterator *iter,
__be32 saddr, __be32 daddr, int flip)
{
struct rds_info_message minfo;
minfo.seq = be64_to_cpu(inc->i_hdr.h_sequence);
minfo.len = be32_to_cpu(inc->i_hdr.h_len);
if (flip) {
minfo.laddr = daddr;
minfo.faddr = saddr;
minfo.lport = inc->i_hdr.h_dport;
minfo.fport = inc->i_hdr.h_sport;
} else {
minfo.laddr = saddr;
minfo.faddr = daddr;
minfo.lport = inc->i_hdr.h_sport;
minfo.fport = inc->i_hdr.h_dport;
}
rds_info_copy(iter, &minfo, sizeof(minfo));
}
Reference in a new issue View git blame Copy permalink