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[minix3.git] / lib / libpuffs / path.c

/*
 * This file contains the procedures that look up path names in the directory
 * system and determine the pnode number that goes with a given path name.
 *
 * Created (based on MFS):
 *   June 2011 (Evgeniy Ivanov)
 */

#include "fs.h"

#include <sys/cdefs.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <assert.h>
#include <errno.h>
#include <puffs.h>
#include <stdlib.h>
#include <string.h>

#include <minix/endpoint.h>
#include <minix/vfsif.h>
#include <minix/libminixfs.h>

#include "puffs.h"
#include "puffs_priv.h"

char dot2[3] = "..";    /* permissions for . and ..                 */

static char *get_name(char *name, char string[NAME_MAX+1]);
static int ltraverse(struct puffs_node *pn, char *suffix);
static int parse_path(ino_t dir_ino, ino_t root_ino, int flags, struct
        puffs_node **res_inop, size_t *offsetp, int *symlinkp);

/*===========================================================================*
 *                             fs_lookup                                     *
 *===========================================================================*/
int fs_lookup(void)
{
  cp_grant_id_t grant;
  int r, r1, flags, symlinks;
  unsigned int len;
  size_t offset = 0, path_size;
  ino_t dir_ino, root_ino;
  struct puffs_node *pn;

  grant         = fs_m_in.m_vfs_fs_lookup.grant_path;
  path_size     = fs_m_in.m_vfs_fs_lookup.path_size;    /* Size of the buffer */
  len           = fs_m_in.m_vfs_fs_lookup.path_len;     /* including terminating nul */
  dir_ino       = fs_m_in.m_vfs_fs_lookup.dir_ino;
  root_ino      = fs_m_in.m_vfs_fs_lookup.root_ino;
  flags         = fs_m_in.m_vfs_fs_lookup.flags;

  /* Check length. */
  if (len > sizeof(user_path)) return(E2BIG);   /* too big for buffer */
  if (len == 0) return(EINVAL);                 /* too small */

  /* Copy the pathname and set up caller's user and group id */
  r = sys_safecopyfrom(VFS_PROC_NR, grant, /*offset*/ 0,
            (vir_bytes) user_path, (size_t) len);
  if (r != OK) return(r);

  /* Verify this is a null-terminated path. */
  if (user_path[len - 1] != '\0') return(EINVAL);

  memset(&credentials, 0, sizeof(credentials));
  if(!(flags & PATH_GET_UCRED)) { /* Do we have to copy uid/gid credentials? */
        caller_uid      = fs_m_in.m_vfs_fs_lookup.uid;
        caller_gid      = fs_m_in.m_vfs_fs_lookup.gid;
  } else {
        if((r=fs_lookup_credentials(&credentials,
                &caller_uid, &caller_gid,
                fs_m_in.m_vfs_fs_lookup.grant_ucred,
                fs_m_in.m_vfs_fs_lookup.ucred_size)) != OK)
                return r;
  }


  /* Lookup pnode */
  pn = NULL;
  r = parse_path(dir_ino, root_ino, flags, &pn, &offset, &symlinks);

  if (symlinks != 0 && (r == ELEAVEMOUNT || r == EENTERMOUNT || r == ESYMLINK)){
        len = strlen(user_path)+1;
        if (len > path_size) return(ENAMETOOLONG);

        r1 = sys_safecopyto(VFS_PROC_NR, grant, (vir_bytes) 0,
                            (vir_bytes) user_path, (size_t) len);
        if (r1 != OK) return(r1);
  }

  if (r == ELEAVEMOUNT || r == ESYMLINK) {
        /* Report offset and the error */
        fs_m_out.m_fs_vfs_lookup.offset = offset;
        fs_m_out.m_fs_vfs_lookup.symloop = symlinks;
        
        return(r);
  }

  if (r != OK && r != EENTERMOUNT) {
        return(r);
  }

  if (r == OK) {
        /* Open pnode */
        pn->pn_count++;
  }

  fs_m_out.m_fs_vfs_lookup.inode        = pn->pn_va.va_fileid;
  fs_m_out.m_fs_vfs_lookup.mode         = pn->pn_va.va_mode;
  fs_m_out.m_fs_vfs_lookup.file_size    = pn->pn_va.va_size;
  fs_m_out.m_fs_vfs_lookup.symloop      = symlinks;
  fs_m_out.m_fs_vfs_lookup.uid          = pn->pn_va.va_uid;
  fs_m_out.m_fs_vfs_lookup.gid          = pn->pn_va.va_gid;

  /* This is only valid for block and character specials. But it doesn't
   * cause any harm to always set the device field. */
  fs_m_out.m_fs_vfs_lookup.device       = pn->pn_va.va_rdev;

  if (r == EENTERMOUNT) {
        fs_m_out.m_fs_vfs_lookup.offset = offset;
  }
  
  return(r);
}


/*===========================================================================*
 *                             parse_path                                    *
 *===========================================================================*/
static int parse_path(
        ino_t dir_ino,
        ino_t root_ino,
        int flags,
        struct puffs_node **res_inop,
        size_t *offsetp,
        int *symlinkp
)
{
  /* Parse the path in user_path, starting at dir_ino. If the path is the empty
   * string, just return dir_ino. It is upto the caller to treat an empty
   * path in a special way. Otherwise, if the path consists of just one or
   * more slash ('/') characters, the path is replaced with ".". Otherwise,
   * just look up the first (or only) component in path after skipping any
   * leading slashes.
   */
  int r, leaving_mount;
  struct puffs_node *pn, *pn_dir;
  char *cp, *next_cp; /* component and next component */
  char component[NAME_MAX+1];

  /* Start parsing path at the first component in user_path */
  cp = user_path;

  /* No symlinks encountered yet */
  *symlinkp = 0;

  /* Find starting pnode according to the request message */
  /* XXX it's deffinitely OK to use nodewalk here */
  if ((pn = puffs_pn_nodewalk(global_pu, 0, &dir_ino)) == NULL) {
        lpuffs_debug("nodewalk failed\n");
        return(ENOENT);
  }

  /* If dir has been removed return ENOENT. */
  if (pn->pn_va.va_nlink == NO_LINK) return(ENOENT);

  /* If the given start pnode is a mountpoint, we must be here because the file
   * system mounted on top returned an ELEAVEMOUNT error. In this case, we must
   * only accept ".." as the first path component.
   */
  leaving_mount = pn->pn_mountpoint; /* True iff pn is a mountpoint */

  /* Scan the path component by component. */
  while (TRUE) {
        if (cp[0] == '\0') {
                /* We're done; either the path was empty or we've parsed all
                   components of the path */

                *res_inop = pn;
                *offsetp += cp - user_path;

                /* Return EENTERMOUNT if we are at a mount point */
                if (pn->pn_mountpoint) return(EENTERMOUNT);

                return(OK);
        }

        while(cp[0] == '/') cp++;
        next_cp = get_name(cp, component);
        if (next_cp == NULL) {
                return(err_code);
        }

        /* Special code for '..'. A process is not allowed to leave a chrooted
         * environment. A lookup of '..' at the root of a mounted filesystem
         * has to return ELEAVEMOUNT. In both cases, the caller needs search
         * permission for the current pnode, as it is used as directory.
         */
        if (strcmp(component, "..") == 0) {
                /* 'pn' is now accessed as directory */
                if ((r = forbidden(pn, X_BIT)) != OK) {
                        return(r);
                }

                if (pn->pn_va.va_fileid == root_ino) {
                        cp = next_cp;
                        continue;       /* Ignore the '..' at a process' root
                                           and move on to the next component */
                }

                if (pn->pn_va.va_fileid == global_pu->pu_pn_root->pn_va.va_fileid
                        && !is_root_fs) {
                        /* Climbing up to parent FS */
                        *offsetp += cp - user_path;
                        return(ELEAVEMOUNT);
                }
        }

        /* Only check for a mount point if we are not coming from one. */
        if (!leaving_mount && pn->pn_mountpoint) {
                /* Going to enter a child FS */

                *res_inop = pn;
                *offsetp += cp - user_path;
                return(EENTERMOUNT);
        }

        /* There is more path.  Keep parsing.
         * If we're leaving a mountpoint, skip directory permission checks.
         */
        pn_dir = pn;
        if ((pn_dir->pn_va.va_mode & I_TYPE) != I_DIRECTORY)  {
                return(ENOTDIR);
        }
        pn = advance(pn_dir, leaving_mount ? dot2 : component, CHK_PERM);
        if (err_code == ELEAVEMOUNT || err_code == EENTERMOUNT)
                err_code = OK;

        if (err_code != OK) {
                return(err_code);
        }
        
        assert(pn != NULL);

        leaving_mount = 0;

        /* The call to advance() succeeded.  Fetch next component. */
        if (S_ISLNK(pn->pn_va.va_mode)) {
                if (next_cp[0] == '\0' && (flags & PATH_RET_SYMLINK)) {
                        *res_inop = pn;
                        *offsetp += next_cp - user_path;
                        return(OK);
                }

                /* Extract path name from the symlink file */
                r = ltraverse(pn, next_cp);
                next_cp = user_path;
                *offsetp = 0;

                /* Symloop limit reached? */
                if (++(*symlinkp) > _POSIX_SYMLOOP_MAX)
                        r = ELOOP;

                if (r != OK)
                        return(r);

                if (next_cp[0] == '/')
                        return(ESYMLINK);

                pn = pn_dir;
        }

        cp = next_cp; /* Process subsequent component in next round */
  }

}


/*===========================================================================*
 *                             ltraverse                                     *
 *===========================================================================*/
static int ltraverse(
        struct puffs_node *pn,  /* symbolic link */
        char *suffix            /* current remaining path. Has to point in the
                                 * user_path buffer
                                 */
)
{
/* Traverse a symbolic link. Copy the link text from the pnode and insert
 * the text into the path. Return error code or report success. Base
 * directory has to be determined according to the first character of the
 * new pathname.
 */
  int r;
  char sp[PATH_MAX];
  size_t llen = PATH_MAX; /* length of link */
  size_t slen;            /* length of suffix */
  PUFFS_MAKECRED(pcr, &global_kcred);


  if (!S_ISLNK(pn->pn_va.va_mode))
        r = EACCES;

  if (global_pu->pu_ops.puffs_node_readlink == NULL)
        return(EINVAL);

  if (global_pu->pu_ops.puffs_node_readlink(global_pu, pn, pcr, sp, &llen) != 0)
        return(EINVAL);

  slen = strlen(suffix);

  /* The path we're parsing looks like this:
   * /already/processed/path/<link> or
   * /already/processed/path/<link>/not/yet/processed/path
   * After expanding the <link>, the path will look like
   * <expandedlink> or
   * <expandedlink>/not/yet/processed
   * In both cases user_path must have enough room to hold <expandedlink>.
   * However, in the latter case we have to move /not/yet/processed to the
   * right place first, before we expand <link>. When strlen(<expandedlink>) is
   * smaller than strlen(/already/processes/path), we move the suffix to the
   * left. Is strlen(<expandedlink>) greater then we move it to the right. Else
   * we do nothing.
   */

  if (slen > 0) { /* Do we have path after the link? */
        /* For simplicity we require that suffix starts with a slash */
        if (suffix[0] != '/') {
                panic("ltraverse: suffix does not start with a slash");
        }

        /* To be able to expand the <link>, we have to move the 'suffix'
         * to the right place.
         */
        if (slen + llen + 1 > sizeof(user_path))
                return(ENAMETOOLONG);/* <expandedlink>+suffix+\0 does not fit*/
        if ((unsigned)(suffix - user_path) != llen) {
                /* Move suffix left or right if needed */
                memmove(&user_path[llen], suffix, slen+1);
        }
  } else {
        if (llen + 1 > sizeof(user_path))
                return(ENAMETOOLONG); /* <expandedlink> + \0 does not fit */

        /* Set terminating nul */
        user_path[llen]= '\0';
  }

  /* Everything is set, now copy the expanded link to user_path */
  memmove(user_path, sp, llen);

  return(OK);
}


/*===========================================================================*
 *                              advance                                      *
 *===========================================================================*/
struct puffs_node *advance(
        struct puffs_node *pn_dir,      /* pnode for directory to be searched */
        char string[NAME_MAX + 1],      /* component name to look for */
        int chk_perm                    /* check permissions when string is
                                         * looked up*/
)
{
/* Given a directory and a component of a path, look up the component in
 * the directory, find the pnode, open it, and return a pointer to its pnode
 * slot.
 * TODO: instead of string, should get pcn.
 */
  struct puffs_node *pn;

  struct puffs_newinfo pni;

  struct puffs_kcn pkcnp;
  PUFFS_MAKECRED(pcr, &global_kcred);
  struct puffs_cn pcn = {&pkcnp, (struct puffs_cred *) __UNCONST(pcr), {0,0,0}};

  enum vtype node_vtype;
  voff_t size;
  dev_t rdev;
  int error;

  err_code = OK;

  /* If 'string' is empty, return an error. */
  if (string[0] == '\0') {
        err_code = ENOENT;
        return(NULL);
  }

  /* Check for NULL. */
  if (pn_dir == NULL)
        return(NULL);

  if (chk_perm) {
        /* Just search permission is checked */
        if (forbidden(pn_dir, X_BIT)) {
                err_code = EACCES;
                return(NULL);
        }
  }

  if (strcmp(string, ".") == 0) {
        /* Otherwise we will fall into trouble: path for pnode to be looked up
         * will be parent path (same pnode as the one to be looked up) +
         * requested path. E.g. after several lookups we might get advance
         * for "." with parent path "/././././././././.".
         *
         * Another problem is that after lookup pnode will be added
         * to the pu_pnodelst, which already contains pnode instance for this
         * pnode. It will cause lot of troubles.
         */
        return pn_dir;
  }

  pni.pni_cookie = (void** )&pn;
  pni.pni_vtype = &node_vtype;
  pni.pni_size = &size;
  pni.pni_rdev = &rdev;

  pcn.pcn_namelen = strlen(string);
  assert(pcn.pcn_namelen <= MAXPATHLEN);
  strcpy(pcn.pcn_name, string);

  if (buildpath) {
        if (puffs_path_pcnbuild(global_pu, &pcn, pn_dir) != 0) {
                lpuffs_debug("pathbuild error\n");
                err_code = ENOENT;
                return(NULL);
        }
  }

  /* lookup *must* be present */
  error = global_pu->pu_ops.puffs_node_lookup(global_pu, pn_dir,
                  &pni, &pcn);

  if (buildpath) {
        if (error) {
                global_pu->pu_pathfree(global_pu, &pcn.pcn_po_full);
                err_code = ENOENT;
                return(NULL);
        } else {
                struct puffs_node *_pn;

                /*
                 * did we get a new node or a
                 * recycled node?
                 */
                _pn = PU_CMAP(global_pu, pn);
                if (_pn->pn_po.po_path == NULL)
                        _pn->pn_po = pcn.pcn_po_full;
                else
                        global_pu->pu_pathfree(global_pu, &pcn.pcn_po_full);
        }
  }

  if (error) {
        err_code = error < 0 ? error : -error;
        return(NULL);
  } else {
        /* In MFS/ext2 it's set by search_dir, puffs_node_lookup error codes are unclear,
         * so we use error variable there
         */
        err_code = OK;
  }

  assert(pn != NULL);

  /* The following test is for "mountpoint/.." where mountpoint is a
   * mountpoint. ".." will refer to the root of the mounted filesystem,
   * but has to become a reference to the parent of the 'mountpoint'
   * directory.
   *
   * This case is recognized by the looked up name pointing to a
   * root pnode, and the directory in which it is held being a
   * root pnode, _and_ the name[1] being '.'. (This is a test for '..'
   * and excludes '.'.)
   */
  if (pn->pn_va.va_fileid == global_pu->pu_pn_root->pn_va.va_fileid) {
          if (pn_dir->pn_va.va_fileid == global_pu->pu_pn_root->pn_va.va_fileid) {
                  if (string[1] == '.') {
                          if (!is_root_fs) {
                                  /* Climbing up mountpoint */
                                  err_code = ELEAVEMOUNT;
                          }
                  }
          }
  }

  /* See if the pnode is mounted on.  If so, switch to root directory of the
   * mounted file system.  The super_block provides the linkage between the
   * pnode mounted on and the root directory of the mounted file system.
   */
  if (pn->pn_mountpoint) {
          /* Mountpoint encountered, report it */
          err_code = EENTERMOUNT;
  }

  return(pn);
}


/*===========================================================================*
 *                              get_name                                     *
 *===========================================================================*/
static char *get_name(
        char *path_name,         /* path name to parse */
        char string[NAME_MAX+1]  /* component extracted from 'old_name' */
)
{
/* Given a pointer to a path name in fs space, 'path_name', copy the first
 * component to 'string' (truncated if necessary, always nul terminated).
 * A pointer to the string after the first component of the name as yet
 * unparsed is returned.  Roughly speaking,
 * 'get_name' = 'path_name' - 'string'.
 *
 * This routine follows the standard convention that /usr/ast, /usr//ast,
 * //usr///ast and /usr/ast/ are all equivalent.
 *
 * If len of component is greater, than allowed, then return 0.
 */
  size_t len;
  char *cp, *ep;

  cp = path_name;

  /* Skip leading slashes */
  while (cp[0] == '/') cp++;

  /* Find the end of the first component */
  ep = cp;
  while (ep[0] != '\0' && ep[0] != '/')
        ep++;

  len = (size_t) (ep - cp);
 
  /* XXX we don't check name_max of fileserver (probably we can't) */
  if (len > NAME_MAX) {
        err_code = ENAMETOOLONG;
        return(NULL);
  }

  /* Special case of the string at cp is empty */
  if (len == 0)
        strcpy(string, ".");  /* Return "." */
  else {
        memcpy(string, cp, len);
        string[len]= '\0';
  }

  return(ep);
}