glibc/nscd/nscd_helper.c

/* Copyright (C) 1998-2002,2003,2004,2005,2006,2007
   Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/un.h>
#include <not-cancel.h>
#include <nis/rpcsvc/nis.h>

#include "nscd-client.h"


ssize_t
__readall (int fd, void *buf, size_t len)
{
  size_t n = len;
  ssize_t ret;
  do
    {
      ret = TEMP_FAILURE_RETRY (__read (fd, buf, n));
      if (ret <= 0)
	break;
      buf = (char *) buf + ret;
      n -= ret;
    }
  while (n > 0);
  return ret < 0 ? ret : len - n;
}


ssize_t
__readvall (int fd, const struct iovec *iov, int iovcnt)
{
  ssize_t ret = TEMP_FAILURE_RETRY (__readv (fd, iov, iovcnt));
  if (ret <= 0)
    return ret;

  size_t total = 0;
  for (int i = 0; i < iovcnt; ++i)
    total += iov[i].iov_len;

  if (ret < total)
    {
      struct iovec iov_buf[iovcnt];
      ssize_t r = ret;

      struct iovec *iovp = memcpy (iov_buf, iov, iovcnt * sizeof (*iov));
      do
	{
	  while (iovp->iov_len <= r)
	    {
	      r -= iovp->iov_len;
	      --iovcnt;
	      ++iovp;
	    }
	  iovp->iov_base = (char *) iovp->iov_base + r;
	  iovp->iov_len -= r;
	  r = TEMP_FAILURE_RETRY (__readv (fd, iovp, iovcnt));
	  if (r <= 0)
	    break;
	  ret += r;
	}
      while (ret < total);
      if (r < 0)
	ret = r;
    }
  return ret;
}


static int
open_socket (request_type type, const char *key, size_t keylen)
{
  int sock = __socket (PF_UNIX, SOCK_STREAM, 0);
  if (sock < 0)
    return -1;

  struct
  {
    request_header req;
    char key[keylen];
  } reqdata;
  size_t real_sizeof_reqdata = sizeof (request_header) + keylen;

  /* Make socket non-blocking.  */
  __fcntl (sock, F_SETFL, O_RDWR | O_NONBLOCK);

  struct sockaddr_un sun;
  sun.sun_family = AF_UNIX;
  strcpy (sun.sun_path, _PATH_NSCDSOCKET);
  if (__connect (sock, (struct sockaddr *) &sun, sizeof (sun)) < 0
      && errno != EINPROGRESS)
    goto out;

  reqdata.req.version = NSCD_VERSION;
  reqdata.req.type = type;
  reqdata.req.key_len = keylen;

  memcpy (reqdata.key, key, keylen);

  bool first_try = true;
  struct timeval tvend;
  /* Fake initializing tvend.  */
  asm ("" : "=m" (tvend));
  while (1)
    {
#ifndef MSG_NOSIGNAL
# define MSG_NOSIGNAL 0
#endif
      ssize_t wres = TEMP_FAILURE_RETRY (__send (sock, &reqdata,
						 real_sizeof_reqdata,
						 MSG_NOSIGNAL));
      if (__builtin_expect (wres == (ssize_t) real_sizeof_reqdata, 1))
	/* We managed to send the request.  */
	return sock;

      if (wres != -1 || errno != EAGAIN)
	/* Something is really wrong, no chance to continue.  */
	break;

      /* The daemon is busy wait for it.  */
      int to;
      struct timeval now;
      (void) __gettimeofday (&now, NULL);
      if (first_try)
	{
	  tvend.tv_usec = now.tv_usec;
	  tvend.tv_sec = now.tv_sec + 5;
	  to = 5 * 1000;
	  first_try = false;
	}
      else
	to = ((tvend.tv_sec - now.tv_sec) * 1000
	      + (tvend.tv_usec - now.tv_usec) / 1000);

      struct pollfd fds[1];
      fds[0].fd = sock;
      fds[0].events = POLLOUT | POLLERR | POLLHUP;
      if (__poll (fds, 1, to) <= 0)
	/* The connection timed out or broke down.  */
	break;

      /* We try to write again.  */
    }

 out:
  close_not_cancel_no_status (sock);

  return -1;
}


void
__nscd_unmap (struct mapped_database *mapped)
{
  assert (mapped->counter == 0);
  __munmap ((void *) mapped->head, mapped->mapsize);
  free (mapped);
}


static int
wait_on_socket (int sock)
{
  struct pollfd fds[1];
  fds[0].fd = sock;
  fds[0].events = POLLIN | POLLERR | POLLHUP;
  int n = __poll (fds, 1, 5 * 1000);
  if (n == -1 && __builtin_expect (errno == EINTR, 0))
    {
      /* Handle the case where the poll() call is interrupted by a
	 signal.  We cannot just use TEMP_FAILURE_RETRY since it might
	 lead to infinite loops.  */
      struct timeval now;
      (void) __gettimeofday (&now, NULL);
      long int end = (now.tv_sec + 5) * 1000 + (now.tv_usec + 500) / 1000;
      while (1)
	{
	  long int timeout = end - (now.tv_sec * 1000
				    + (now.tv_usec + 500) / 1000);
	  n = __poll (fds, 1, timeout);
	  if (n != -1 || errno != EINTR)
	    break;
	  (void) __gettimeofday (&now, NULL);
	}
    }

  return n;
}


/* Try to get a file descriptor for the shared meory segment
   containing the database.  */
static struct mapped_database *
get_mapping (request_type type, const char *key,
	     struct mapped_database **mappedp)
{
  struct mapped_database *result = NO_MAPPING;
#ifdef SCM_RIGHTS
  const size_t keylen = strlen (key) + 1;
  int saved_errno = errno;

  int mapfd = -1;
  char resdata[keylen];

  /* Open a socket and send the request.  */
  int sock = open_socket (type, key, keylen);
  if (sock < 0)
    goto out;

  /* Room for the data sent along with the file descriptor.  We expect
     the key name back.  */
  struct iovec iov[1];
  iov[0].iov_base = resdata;
  iov[0].iov_len = keylen;

  union
  {
    struct cmsghdr hdr;
    char bytes[CMSG_SPACE (sizeof (int))];
  } buf;
  struct msghdr msg = { .msg_iov = iov, .msg_iovlen = 1,
			.msg_control = buf.bytes,
			.msg_controllen = sizeof (buf) };
  struct cmsghdr *cmsg = CMSG_FIRSTHDR (&msg);

  cmsg->cmsg_level = SOL_SOCKET;
  cmsg->cmsg_type = SCM_RIGHTS;
  cmsg->cmsg_len = CMSG_LEN (sizeof (int));

  /* This access is well-aligned since BUF is correctly aligned for an
     int and CMSG_DATA preserves this alignment.  */
  *(int *) CMSG_DATA (cmsg) = -1;

  msg.msg_controllen = cmsg->cmsg_len;

  if (wait_on_socket (sock) <= 0)
    goto out_close2;

  if (__builtin_expect (TEMP_FAILURE_RETRY (__recvmsg (sock, &msg, 0))
			!= keylen, 0))
    goto out_close2;

  mapfd = *(int *) CMSG_DATA (cmsg);

  if (__builtin_expect (CMSG_FIRSTHDR (&msg)->cmsg_len
			!= CMSG_LEN (sizeof (int)), 0))
    goto out_close;

  struct stat64 st;
  if (__builtin_expect (strcmp (resdata, key) != 0, 0)
      || __builtin_expect (fstat64 (mapfd, &st) != 0, 0)
      || __builtin_expect (st.st_size < sizeof (struct database_pers_head), 0))
    goto out_close;

  struct database_pers_head head;
  if (__builtin_expect (TEMP_FAILURE_RETRY (__pread (mapfd, &head,
						     sizeof (head), 0))
			!= sizeof (head), 0))
    goto out_close;

  if (__builtin_expect (head.version != DB_VERSION, 0)
      || __builtin_expect (head.header_size != sizeof (head), 0)
      /* This really should not happen but who knows, maybe the update
	 thread got stuck.  */
      || __builtin_expect (! head.nscd_certainly_running
			   && head.timestamp + MAPPING_TIMEOUT < time (NULL),
			   0))
    goto out_close;

  size_t size = (sizeof (head) + roundup (head.module * sizeof (ref_t), ALIGN)
		 + head.data_size);

  if (__builtin_expect (st.st_size < size, 0))
    goto out_close;

  /* The file is large enough, map it now.  */
  void *mapping = __mmap (NULL, size, PROT_READ, MAP_SHARED, mapfd, 0);
  if (__builtin_expect (mapping != MAP_FAILED, 1))
    {
      /* Allocate a record for the mapping.  */
      struct mapped_database *newp = malloc (sizeof (*newp));
      if (newp == NULL)
	{
	  /* Ugh, after all we went through the memory allocation failed.  */
	  __munmap (mapping, size);
	  goto out_close;
	}

      newp->head = mapping;
      newp->data = ((char *) mapping + head.header_size
		    + roundup (head.module * sizeof (ref_t), ALIGN));
      newp->mapsize = size;
      newp->datasize = head.data_size;
      /* Set counter to 1 to show it is usable.  */
      newp->counter = 1;

      result = newp;
    }

 out_close:
  __close (mapfd);
 out_close2:
  __close (sock);
 out:
  __set_errno (saved_errno);
#endif	/* SCM_RIGHTS */

  struct mapped_database *oldval = *mappedp;
  *mappedp = result;

  if (oldval != NULL && atomic_decrement_val (&oldval->counter) == 0)
    __nscd_unmap (oldval);

  return result;
}


struct mapped_database *
__nscd_get_map_ref (request_type type, const char *name,
		    volatile struct locked_map_ptr *mapptr, int *gc_cyclep)
{
  struct mapped_database *cur = mapptr->mapped;
  if (cur == NO_MAPPING)
    return cur;

  int cnt = 0;
  while (__builtin_expect (atomic_compare_and_exchange_val_acq (&mapptr->lock,
								1, 0) != 0, 0))
    {
      // XXX Best number of rounds?
      if (__builtin_expect (++cnt > 5, 0))
	return NO_MAPPING;

      atomic_delay ();
    }

  cur = mapptr->mapped;

  if (__builtin_expect (cur != NO_MAPPING, 1))
    {
      /* If not mapped or timestamp not updated, request new map.  */
      if (cur == NULL
	  || (cur->head->nscd_certainly_running == 0
	      && cur->head->timestamp + MAPPING_TIMEOUT < time (NULL))
	  || cur->head->data_size > cur->datasize)
	cur = get_mapping (type, name,
			   (struct mapped_database **) &mapptr->mapped);

      if (__builtin_expect (cur != NO_MAPPING, 1))
	{
	  if (__builtin_expect (((*gc_cyclep = cur->head->gc_cycle) & 1) != 0,
				0))
	    cur = NO_MAPPING;
	  else
	    atomic_increment (&cur->counter);
	}
    }

  mapptr->lock = 0;

  return cur;
}


/* Don't return const struct datahead *, as eventhough the record
   is normally constant, it can change arbitrarily during nscd
   garbage collection.  */
struct datahead *
__nscd_cache_search (request_type type, const char *key, size_t keylen,
		     const struct mapped_database *mapped)
{
  unsigned long int hash = __nis_hash (key, keylen) % mapped->head->module;
  size_t datasize = mapped->datasize;

  ref_t work = mapped->head->array[hash];
  while (work != ENDREF && work + sizeof (struct hashentry) <= datasize)
    {
      struct hashentry *here = (struct hashentry *) (mapped->data + work);

#ifndef _STRING_ARCH_unaligned
      /* Although during garbage collection when moving struct hashentry
	 records around we first copy from old to new location and then
	 adjust pointer from previous hashentry to it, there is no barrier
	 between those memory writes.  It is very unlikely to hit it,
	 so check alignment only if a misaligned load can crash the
	 application.  */
      if ((uintptr_t) here & (__alignof__ (*here) - 1))
	return NULL;
#endif

      if (type == here->type
	  && keylen == here->len
	  && here->key + keylen <= datasize
	  && memcmp (key, mapped->data + here->key, keylen) == 0
	  && here->packet + sizeof (struct datahead) <= datasize)
	{
	  /* We found the entry.  Increment the appropriate counter.  */
	  struct datahead *dh
	    = (struct datahead *) (mapped->data + here->packet);

#ifndef _STRING_ARCH_unaligned
	  if ((uintptr_t) dh & (__alignof__ (*dh) - 1))
	    return NULL;
#endif

	  /* See whether we must ignore the entry or whether something
	     is wrong because garbage collection is in progress.  */
	  if (dh->usable && here->packet + dh->allocsize <= datasize)
	    return dh;
	}

      work = here->next;
    }

  return NULL;
}


/* Create a socket connected to a name. */
int
__nscd_open_socket (const char *key, size_t keylen, request_type type,
		    void *response, size_t responselen)
{
  /* This should never happen and it is something the nscd daemon
     enforces, too.  He it helps to limit the amount of stack
     used.  */
  if (keylen > MAXKEYLEN)
    return -1;

  int saved_errno = errno;

  int sock = open_socket (type, key, keylen);
  if (sock >= 0)
    {
      /* Wait for data.  */
      if (wait_on_socket (sock) > 0)
	{
	  ssize_t nbytes = TEMP_FAILURE_RETRY (__read (sock, response,
						       responselen));
	  if (nbytes == (ssize_t) responselen)
	    return sock;
	}

      close_not_cancel_no_status (sock);
    }

  __set_errno (saved_errno);

  return -1;
}