vm: fix potential null deref

[minix.git] / servers / mfs / read.c

#include "fs.h"
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <minix/com.h>
#include <minix/u64.h>
#include "buf.h"
#include "inode.h"
#include "super.h"
#include <minix/vfsif.h>
#include <assert.h>


static struct buf *rahead(struct inode *rip, block_t baseblock, u64_t
        position, unsigned bytes_ahead);
static int rw_chunk(struct inode *rip, u64_t position, unsigned off,
        size_t chunk, unsigned left, int rw_flag, cp_grant_id_t gid, unsigned
        buf_off, unsigned int block_size, int *completed);


/*===========================================================================*
 *                              fs_readwrite                                 *
 *===========================================================================*/
int fs_readwrite(void)
{
  int r, rw_flag, block_spec;
  int regular;
  cp_grant_id_t gid;
  off_t position, f_size, bytes_left;
  unsigned int off, cum_io, block_size, chunk;
  mode_t mode_word;
  int completed;
  struct inode *rip;
  size_t nrbytes;
  
  r = OK;
  
  /* Find the inode referred */
  if ((rip = find_inode(fs_dev, (ino_t) fs_m_in.REQ_INODE_NR)) == NULL)
        return(EINVAL);

  mode_word = rip->i_mode & I_TYPE;
  regular = (mode_word == I_REGULAR || mode_word == I_NAMED_PIPE);
  block_spec = (mode_word == I_BLOCK_SPECIAL ? 1 : 0);
  
  /* Determine blocksize */
  if (block_spec) {
        block_size = get_block_size( (dev_t) rip->i_zone[0]);
        f_size = MAX_FILE_POS;
  } else {
        block_size = rip->i_sp->s_block_size;
        f_size = rip->i_size;
  }

  /* Get the values from the request message */ 
  rw_flag = (fs_m_in.m_type == REQ_READ ? READING : WRITING);
  gid = (cp_grant_id_t) fs_m_in.REQ_GRANT;
  position = (off_t) fs_m_in.REQ_SEEK_POS_LO;
  nrbytes = (size_t) fs_m_in.REQ_NBYTES;
  
  lmfs_reset_rdwt_err();

  /* If this is file i/o, check we can write */
  if (rw_flag == WRITING && !block_spec) {
          if(rip->i_sp->s_rd_only) 
                  return EROFS;

          /* Check in advance to see if file will grow too big. */
          if (position > (off_t) (rip->i_sp->s_max_size - nrbytes))
                  return(EFBIG);

          /* Clear the zone containing present EOF if hole about
           * to be created.  This is necessary because all unwritten
           * blocks prior to the EOF must read as zeros.
           */
          if(position > f_size) clear_zone(rip, f_size, 0);
  }

  /* If this is block i/o, check we can write */
  if(block_spec && rw_flag == WRITING &&
        (dev_t) rip->i_zone[0] == superblock.s_dev && superblock.s_rd_only)
                return EROFS;
              
  cum_io = 0;
  /* Split the transfer into chunks that don't span two blocks. */
  while (nrbytes > 0) {
          off = ((unsigned int) position) % block_size; /* offset in blk*/
          chunk = min(nrbytes, block_size - off);

          if (rw_flag == READING) {
                  bytes_left = f_size - position;
                  if (position >= f_size) break;        /* we are beyond EOF */
                  if (chunk > (unsigned int) bytes_left) chunk = bytes_left;
          }
          
          /* Read or write 'chunk' bytes. */
          r = rw_chunk(rip, cvul64((unsigned long) position), off, chunk,
                       nrbytes, rw_flag, gid, cum_io, block_size, &completed);

          if (r != OK) break;   /* EOF reached */
          if (lmfs_rdwt_err() < 0) break;

          /* Update counters and pointers. */
          nrbytes -= chunk;     /* bytes yet to be read */
          cum_io += chunk;      /* bytes read so far */
          position += (off_t) chunk;    /* position within the file */
  }

  fs_m_out.RES_SEEK_POS_LO = position; /* It might change later and the VFS
                                           has to know this value */
  
  /* On write, update file size and access time. */
  if (rw_flag == WRITING) {
          if (regular || mode_word == I_DIRECTORY) {
                  if (position > f_size) rip->i_size = position;
          }
  } 

  rip->i_seek = NO_SEEK;

  if (lmfs_rdwt_err() != OK) r = lmfs_rdwt_err();       /* check for disk error */
  if (lmfs_rdwt_err() == END_OF_FILE) r = OK;

  /* even on a ROFS, writing to a device node on it is fine, 
   * just don't update the inode stats for it. And dito for reading.
   */
  if (r == OK && !rip->i_sp->s_rd_only) {
          if (rw_flag == READING) rip->i_update |= ATIME;
          if (rw_flag == WRITING) rip->i_update |= CTIME | MTIME;
          IN_MARKDIRTY(rip);            /* inode is thus now dirty */
  }
  
  fs_m_out.RES_NBYTES = cum_io;
  
  return(r);
}


/*===========================================================================*
 *                              fs_breadwrite                                *
 *===========================================================================*/
int fs_breadwrite(void)
{
  int r, rw_flag, completed;
  cp_grant_id_t gid;
  u64_t position;
  unsigned int off, cum_io, chunk, block_size;
  size_t nrbytes;
  dev_t target_dev;

  /* Pseudo inode for rw_chunk */
  struct inode rip;
  
  r = OK;

  target_dev = (dev_t) fs_m_in.REQ_DEV2;
  
  /* Get the values from the request message */ 
  rw_flag = (fs_m_in.m_type == REQ_BREAD ? READING : WRITING);
  gid = (cp_grant_id_t) fs_m_in.REQ_GRANT;
  position = make64((unsigned long) fs_m_in.REQ_SEEK_POS_LO,
                    (unsigned long) fs_m_in.REQ_SEEK_POS_HI);
  nrbytes = (size_t) fs_m_in.REQ_NBYTES;
  
  block_size = get_block_size(target_dev);

  /* Don't block-write to a RO-mounted filesystem. */
  if(superblock.s_dev == target_dev && superblock.s_rd_only)
        return EROFS;

  rip.i_zone[0] = (zone_t) target_dev;
  rip.i_mode = I_BLOCK_SPECIAL;
  rip.i_size = 0;

  lmfs_reset_rdwt_err();
  
  cum_io = 0;
  /* Split the transfer into chunks that don't span two blocks. */
  while (nrbytes > 0) {
          off = rem64u(position, block_size);   /* offset in blk*/
          chunk = min(nrbytes, block_size - off);

          /* Read or write 'chunk' bytes. */
          r = rw_chunk(&rip, position, off, chunk, nrbytes, rw_flag, gid,
                       cum_io, block_size, &completed);

          if (r != OK) break;   /* EOF reached */
          if (lmfs_rdwt_err() < 0) break;

          /* Update counters and pointers. */
          nrbytes -= chunk;             /* bytes yet to be read */
          cum_io += chunk;              /* bytes read so far */
          position = add64ul(position, chunk);  /* position within the file */
  }
  
  fs_m_out.RES_SEEK_POS_LO = ex64lo(position); 
  fs_m_out.RES_SEEK_POS_HI = ex64hi(position); 
  
  if (lmfs_rdwt_err() != OK) r = lmfs_rdwt_err();       /* check for disk error */
  if (lmfs_rdwt_err() == END_OF_FILE) r = OK;

  fs_m_out.RES_NBYTES = cum_io;
  
  return(r);
}


/*===========================================================================*
 *                              rw_chunk                                     *
 *===========================================================================*/
static int rw_chunk(rip, position, off, chunk, left, rw_flag, gid,
 buf_off, block_size, completed)
register struct inode *rip;     /* pointer to inode for file to be rd/wr */
u64_t position;                 /* position within file to read or write */
unsigned off;                   /* off within the current block */
unsigned int chunk;             /* number of bytes to read or write */
unsigned left;                  /* max number of bytes wanted after position */
int rw_flag;                    /* READING or WRITING */
cp_grant_id_t gid;              /* grant */
unsigned buf_off;               /* offset in grant */
unsigned int block_size;        /* block size of FS operating on */
int *completed;                 /* number of bytes copied */
{
/* Read or write (part of) a block. */

  register struct buf *bp;
  register int r = OK;
  int n, block_spec;
  block_t b;
  dev_t dev;

  *completed = 0;

  block_spec = (rip->i_mode & I_TYPE) == I_BLOCK_SPECIAL;

  if (block_spec) {
        b = div64u(position, block_size);
        dev = (dev_t) rip->i_zone[0];
  } else {
        if (ex64hi(position) != 0)
                panic("rw_chunk: position too high");
        b = read_map(rip, (off_t) ex64lo(position));
        dev = rip->i_dev;
  }

  if (!block_spec && b == NO_BLOCK) {
        if (rw_flag == READING) {
                /* Reading from a nonexistent block.  Must read as all zeros.*/
                bp = get_block(NO_DEV, NO_BLOCK, NORMAL);    /* get a buffer */
                zero_block(bp);
        } else {
                /* Writing to a nonexistent block. Create and enter in inode.*/
                if ((bp = new_block(rip, (off_t) ex64lo(position))) == NULL)
                        return(err_code);
        }
  } else if (rw_flag == READING) {
        /* Read and read ahead if convenient. */
        bp = rahead(rip, b, position, left);
  } else {
        /* Normally an existing block to be partially overwritten is first read
         * in.  However, a full block need not be read in.  If it is already in
         * the cache, acquire it, otherwise just acquire a free buffer.
         */
        n = (chunk == block_size ? NO_READ : NORMAL);
        if (!block_spec && off == 0 && (off_t) ex64lo(position) >= rip->i_size) 
                n = NO_READ;
        bp = get_block(dev, b, n);
  }

  /* In all cases, bp now points to a valid buffer. */
  if (bp == NULL) 
        panic("bp not valid in rw_chunk; this can't happen");
  
  if (rw_flag == WRITING && chunk != block_size && !block_spec &&
      (off_t) ex64lo(position) >= rip->i_size && off == 0) {
        zero_block(bp);
  }

  if (rw_flag == READING) {
        /* Copy a chunk from the block buffer to user space. */
        r = sys_safecopyto(VFS_PROC_NR, gid, (vir_bytes) buf_off,
                           (vir_bytes) (b_data(bp)+off), (size_t) chunk);
  } else {
        /* Copy a chunk from user space to the block buffer. */
        r = sys_safecopyfrom(VFS_PROC_NR, gid, (vir_bytes) buf_off,
                             (vir_bytes) (b_data(bp)+off), (size_t) chunk);
        MARKDIRTY(bp);
  }
  
  n = (off + chunk == block_size ? FULL_DATA_BLOCK : PARTIAL_DATA_BLOCK);
  put_block(bp, n);

  return(r);
}


/*===========================================================================*
 *                              read_map                                     *
 *===========================================================================*/
block_t read_map(rip, position)
register struct inode *rip;     /* ptr to inode to map from */
off_t position;                 /* position in file whose blk wanted */
{
/* Given an inode and a position within the corresponding file, locate the
 * block (not zone) number in which that position is to be found and return it.
 */

  struct buf *bp;
  zone_t z;
  int scale, boff, index, zind;
  unsigned int dzones, nr_indirects;
  block_t b;
  unsigned long excess, zone, block_pos;
  
  scale = rip->i_sp->s_log_zone_size;   /* for block-zone conversion */
  block_pos = position/rip->i_sp->s_block_size; /* relative blk # in file */
  zone = block_pos >> scale;    /* position's zone */
  boff = (int) (block_pos - (zone << scale) ); /* relative blk # within zone */
  dzones = rip->i_ndzones;
  nr_indirects = rip->i_nindirs;

  /* Is 'position' to be found in the inode itself? */
  if (zone < dzones) {
        zind = (int) zone;      /* index should be an int */
        z = rip->i_zone[zind];
        if (z == NO_ZONE) return(NO_BLOCK);
        b = (block_t) ((z << scale) + boff);
        return(b);
  }

  /* It is not in the inode, so it must be single or double indirect. */
  excess = zone - dzones;       /* first Vx_NR_DZONES don't count */

  if (excess < nr_indirects) {
        /* 'position' can be located via the single indirect block. */
        z = rip->i_zone[dzones];
  } else {
        /* 'position' can be located via the double indirect block. */
        if ( (z = rip->i_zone[dzones+1]) == NO_ZONE) return(NO_BLOCK);
        excess -= nr_indirects;                 /* single indir doesn't count*/
        b = (block_t) z << scale;
        ASSERT(rip->i_dev != NO_DEV);
        index = (int) (excess/nr_indirects);
        if ((unsigned int) index > rip->i_nindirs)
                return(NO_BLOCK);       /* Can't go beyond double indirects */
        bp = get_block(rip->i_dev, b, NORMAL);  /* get double indirect block */
        ASSERT(lmfs_dev(bp) != NO_DEV);
        ASSERT(lmfs_dev(bp) == rip->i_dev);
        z = rd_indir(bp, index);                /* z= zone for single*/
        put_block(bp, INDIRECT_BLOCK);          /* release double ind block */
        excess = excess % nr_indirects;         /* index into single ind blk */
  }

  /* 'z' is zone num for single indirect block; 'excess' is index into it. */
  if (z == NO_ZONE) return(NO_BLOCK);
  b = (block_t) z << scale;                     /* b is blk # for single ind */
  bp = get_block(rip->i_dev, b, NORMAL);        /* get single indirect block */
  z = rd_indir(bp, (int) excess);               /* get block pointed to */
  put_block(bp, INDIRECT_BLOCK);                /* release single indir blk */
  if (z == NO_ZONE) return(NO_BLOCK);
  b = (block_t) ((z << scale) + boff);
  return(b);
}


/*===========================================================================*
 *                              rd_indir                                     *
 *===========================================================================*/
zone_t rd_indir(bp, index)
struct buf *bp;                 /* pointer to indirect block */
int index;                      /* index into *bp */
{
/* Given a pointer to an indirect block, read one entry.  The reason for
 * making a separate routine out of this is that there are four cases:
 * V1 (IBM and 68000), and V2 (IBM and 68000).
 */

  struct super_block *sp;
  zone_t zone;                  /* V2 zones are longs (shorts in V1) */

  if(bp == NULL)
        panic("rd_indir() on NULL");

  sp = get_super(lmfs_dev(bp)); /* need super block to find file sys type */

  /* read a zone from an indirect block */
  if (sp->s_version == V1)
        zone = (zone_t) conv2(sp->s_native, (int)  b_v1_ind(bp)[index]);
  else
        zone = (zone_t) conv4(sp->s_native, (long) b_v2_ind(bp)[index]);

  if (zone != NO_ZONE &&
                (zone < (zone_t) sp->s_firstdatazone || zone >= sp->s_zones)) {
        printf("Illegal zone number %ld in indirect block, index %d\n",
               (long) zone, index);
        panic("check file system");
  }
  
  return(zone);
}

/*===========================================================================*
 *                              rahead                                       *
 *===========================================================================*/
static struct buf *rahead(rip, baseblock, position, bytes_ahead)
register struct inode *rip;     /* pointer to inode for file to be read */
block_t baseblock;              /* block at current position */
u64_t position;                 /* position within file */
unsigned bytes_ahead;           /* bytes beyond position for immediate use */
{
/* Fetch a block from the cache or the device.  If a physical read is
 * required, prefetch as many more blocks as convenient into the cache.
 * This usually covers bytes_ahead and is at least BLOCKS_MINIMUM.
 * The device driver may decide it knows better and stop reading at a
 * cylinder boundary (or after an error).  Rw_scattered() puts an optional
 * flag on all reads to allow this.
 */
/* Minimum number of blocks to prefetch. */
  int nr_bufs = lmfs_nr_bufs();
# define BLOCKS_MINIMUM         (nr_bufs < 50 ? 18 : 32)
  int block_spec, scale, read_q_size;
  unsigned int blocks_ahead, fragment, block_size;
  block_t block, blocks_left;
  off_t ind1_pos;
  dev_t dev;
  struct buf *bp;
  static unsigned int readqsize = 0;
  static struct buf **read_q;

  if(readqsize != nr_bufs) {
        if(readqsize > 0) {
                assert(read_q != NULL);
                free(read_q);
        }
        if(!(read_q = malloc(sizeof(read_q[0])*nr_bufs)))
                panic("couldn't allocate read_q");
        readqsize = nr_bufs;
  }

  block_spec = (rip->i_mode & I_TYPE) == I_BLOCK_SPECIAL;
  if (block_spec) 
        dev = (dev_t) rip->i_zone[0];
  else 
        dev = rip->i_dev;
  
  block_size = get_block_size(dev);

  block = baseblock;
  bp = get_block(dev, block, PREFETCH);
  assert(bp != NULL);
  if (lmfs_dev(bp) != NO_DEV) return(bp);

  /* The best guess for the number of blocks to prefetch:  A lot.
   * It is impossible to tell what the device looks like, so we don't even
   * try to guess the geometry, but leave it to the driver.
   *
   * The floppy driver can read a full track with no rotational delay, and it
   * avoids reading partial tracks if it can, so handing it enough buffers to
   * read two tracks is perfect.  (Two, because some diskette types have
   * an odd number of sectors per track, so a block may span tracks.)
   *
   * The disk drivers don't try to be smart.  With todays disks it is
   * impossible to tell what the real geometry looks like, so it is best to
   * read as much as you can.  With luck the caching on the drive allows
   * for a little time to start the next read.
   *
   * The current solution below is a bit of a hack, it just reads blocks from
   * the current file position hoping that more of the file can be found.  A
   * better solution must look at the already available zone pointers and
   * indirect blocks (but don't call read_map!).
   */

  fragment = rem64u(position, block_size);
  position = sub64u(position, fragment);
  bytes_ahead += fragment;

  blocks_ahead = (bytes_ahead + block_size - 1) / block_size;

  if (block_spec && rip->i_size == 0) {
        blocks_left = (block_t) NR_IOREQS;
  } else {
        blocks_left = (block_t) (rip->i_size-ex64lo(position)+(block_size-1)) /
                                                                block_size;

        /* Go for the first indirect block if we are in its neighborhood. */
        if (!block_spec) {
                scale = rip->i_sp->s_log_zone_size;
                ind1_pos = (off_t) rip->i_ndzones * (block_size << scale);
                if ((off_t) ex64lo(position) <= ind1_pos &&
                     rip->i_size > ind1_pos) {
                        blocks_ahead++;
                        blocks_left++;
                }
        }
  }

  /* No more than the maximum request. */
  if (blocks_ahead > NR_IOREQS) blocks_ahead = NR_IOREQS;

  /* Read at least the minimum number of blocks, but not after a seek. */
  if (blocks_ahead < BLOCKS_MINIMUM && rip->i_seek == NO_SEEK)
        blocks_ahead = BLOCKS_MINIMUM;

  /* Can't go past end of file. */
  if (blocks_ahead > blocks_left) blocks_ahead = blocks_left;

  read_q_size = 0;

  /* Acquire block buffers. */
  for (;;) {
        read_q[read_q_size++] = bp;

        if (--blocks_ahead == 0) break;

        /* Don't trash the cache, leave 4 free. */
        if (lmfs_bufs_in_use() >= nr_bufs - 4) break;

        block++;

        bp = get_block(dev, block, PREFETCH);
        if (lmfs_dev(bp) != NO_DEV) {
                /* Oops, block already in the cache, get out. */
                put_block(bp, FULL_DATA_BLOCK);
                break;
        }
  }
  lmfs_rw_scattered(dev, read_q, read_q_size, READING);
  return(get_block(dev, baseblock, NORMAL));
}


/*===========================================================================*
 *                              fs_getdents                                  *
 *===========================================================================*/
int fs_getdents(void)
{
#define GETDENTS_BUFSIZE        (sizeof(struct dirent) + MFS_NAME_MAX + 1)
#define GETDENTS_ENTRIES        8
  static char getdents_buf[GETDENTS_BUFSIZE * GETDENTS_ENTRIES];
  register struct inode *rip;
  int o, r, done;
  unsigned int block_size, len, reclen;
  ino_t ino;
  block_t b;
  cp_grant_id_t gid;
  size_t size, tmpbuf_off, userbuf_off;
  off_t pos, off, block_pos, new_pos, ent_pos;
  struct buf *bp;
  struct direct *dp;
  struct dirent *dep;
  char *cp;

  ino = (ino_t) fs_m_in.REQ_INODE_NR;
  gid = (gid_t) fs_m_in.REQ_GRANT;
  size = (size_t) fs_m_in.REQ_MEM_SIZE;
  pos = (off_t) fs_m_in.REQ_SEEK_POS_LO;

  /* Check whether the position is properly aligned */
  if( (unsigned int) pos % DIR_ENTRY_SIZE)
          return(ENOENT);
  
  if( (rip = get_inode(fs_dev, ino)) == NULL) 
          return(EINVAL);

  block_size = rip->i_sp->s_block_size;
  off = (pos % block_size);             /* Offset in block */
  block_pos = pos - off;
  done = FALSE;         /* Stop processing directory blocks when done is set */

  tmpbuf_off = 0;       /* Offset in getdents_buf */
  memset(getdents_buf, '\0', sizeof(getdents_buf));     /* Avoid leaking any data */
  userbuf_off = 0;      /* Offset in the user's buffer */

  /* The default position for the next request is EOF. If the user's buffer
   * fills up before EOF, new_pos will be modified. */
  new_pos = rip->i_size;

  for(; block_pos < rip->i_size; block_pos += block_size) {
        b = read_map(rip, block_pos);   /* get block number */
          
        /* Since directories don't have holes, 'b' cannot be NO_BLOCK. */
        bp = get_block(rip->i_dev, b, NORMAL);  /* get a dir block */

        assert(bp != NULL);

          /* Search a directory block. */
          if (block_pos < pos)
                  dp = &b_dir(bp)[off / DIR_ENTRY_SIZE];
          else
                  dp = &b_dir(bp)[0];
          for (; dp < &b_dir(bp)[NR_DIR_ENTRIES(block_size)]; dp++) {
                  if (dp->mfs_d_ino == 0) 
                          continue;     /* Entry is not in use */

                  /* Compute the length of the name */
                  cp = memchr(dp->mfs_d_name, '\0', sizeof(dp->mfs_d_name));
                  if (cp == NULL)
                          len = sizeof(dp->mfs_d_name);
                  else
                          len = cp - (dp->mfs_d_name);
                
                  /* Compute record length */
                  reclen = offsetof(struct dirent, d_name) + len + 1;
                  o = (reclen % sizeof(long));
                  if (o != 0)
                          reclen += sizeof(long) - o;

                  /* Need the position of this entry in the directory */
                  ent_pos = block_pos + ((char *) dp - (char *) bp->data);

                if (userbuf_off + tmpbuf_off + reclen >= size) {
                          /* The user has no space for one more record */
                          done = TRUE;

                          /* Record the position of this entry, it is the
                           * starting point of the next request (unless the
                           * postion is modified with lseek).
                           */
                          new_pos = ent_pos;
                          break;
                }

                if (tmpbuf_off + reclen >= GETDENTS_BUFSIZE*GETDENTS_ENTRIES) {
                          r = sys_safecopyto(VFS_PROC_NR, gid,
                                             (vir_bytes) userbuf_off, 
                                             (vir_bytes) getdents_buf,
                                             (size_t) tmpbuf_off);
                          if (r != OK) {
                                put_inode(rip);
                                return(r);
                          }

                          userbuf_off += tmpbuf_off;
                          tmpbuf_off = 0;
                }

                dep = (struct dirent *) &getdents_buf[tmpbuf_off];
                dep->d_ino = dp->mfs_d_ino;
                dep->d_off = ent_pos;
                dep->d_reclen = (unsigned short) reclen;
                memcpy(dep->d_name, dp->mfs_d_name, len);
                dep->d_name[len] = '\0';
                tmpbuf_off += reclen;
        }

        put_block(bp, DIRECTORY_BLOCK);
        if (done)
                break;
  }

  if (tmpbuf_off != 0) {
        r = sys_safecopyto(VFS_PROC_NR, gid, (vir_bytes) userbuf_off,
                             (vir_bytes) getdents_buf, (size_t) tmpbuf_off);
        if (r != OK) {
                put_inode(rip);
                return(r);
        }

        userbuf_off += tmpbuf_off;
  }

  if (done && userbuf_off == 0)
          r = EINVAL;           /* The user's buffer is too small */
  else {
          fs_m_out.RES_NBYTES = userbuf_off;
          fs_m_out.RES_SEEK_POS_LO = new_pos;
          if(!rip->i_sp->s_rd_only) {
                  rip->i_update |= ATIME;
                  IN_MARKDIRTY(rip);
          }
          r = OK;
  }

  put_inode(rip);               /* release the inode */
  return(r);
}