sys/kern/vfs_lookup.c

/*
 * Copyright (c) 1982, 1986, 1989 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)vfs_lookup.c  7.32 (Berkeley) 5/21/91
 *      $Id$
 */

#include "param.h"
#include "syslimits.h"
#include "time.h"
#include "namei.h"
#include "vnode.h"
#include "mount.h"
#include "errno.h"
#include "malloc.h"
#include "filedesc.h"
#include "proc.h"

#ifdef KTRACE
#include "ktrace.h"
#endif

/*
 * Convert a pathname into a pointer to a locked inode.
 *
 * The FOLLOW flag is set when symbolic links are to be followed
 * when they occur at the end of the name translation process.
 * Symbolic links are always followed for all other pathname
 * components other than the last.
 *
 * The segflg defines whether the name is to be copied from user
 * space or kernel space.
 *
 * Overall outline of namei:
 *
 *      copy in name
 *      get starting directory
 *      while (!done && !error) {
 *              call lookup to search path.
 *              if symbolic link, massage name in buffer and continue
 *      }
 */
namei(ndp, p)
        register struct nameidata *ndp;
        struct proc *p;
{
        register struct filedesc *fdp;  /* pointer to file descriptor state */
        register char *cp;              /* pointer into pathname argument */
        register struct vnode *dp;      /* the directory we are searching */
        struct iovec aiov;              /* uio for reading symbolic links */
        struct uio auio;
        int error, linklen;

        ndp->ni_cred = p->p_ucred;
        fdp = p->p_fd;

        /*
         * Get a buffer for the name to be translated, and copy the
         * name into the buffer.
         */
        if ((ndp->ni_nameiop & HASBUF) == 0)
                MALLOC(ndp->ni_pnbuf, caddr_t, MAXPATHLEN, M_NAMEI, M_WAITOK);
        if (ndp->ni_segflg == UIO_SYSSPACE)
                error = copystr(ndp->ni_dirp, ndp->ni_pnbuf,
                            MAXPATHLEN, &ndp->ni_pathlen);
        else
                error = copyinstr(ndp->ni_dirp, ndp->ni_pnbuf,
                            MAXPATHLEN, &ndp->ni_pathlen);
        if (error) {
                free(ndp->ni_pnbuf, M_NAMEI);
                ndp->ni_vp = NULL;
                return (error);
        }
        ndp->ni_loopcnt = 0;
#ifdef KTRACE
        if (KTRPOINT(p, KTR_NAMEI))
                ktrnamei(p->p_tracep, ndp->ni_pnbuf);
#endif

        /*
         * Get starting point for the translation.
         */
        if ((ndp->ni_rootdir = fdp->fd_rdir) == NULL)
                ndp->ni_rootdir = rootdir;
        dp = fdp->fd_cdir;
        VREF(dp);
        for (;;) {
                /*
                 * Check if root directory should replace current directory.
                 * Done at start of translation and after symbolic link.
                 */
                ndp->ni_ptr = ndp->ni_pnbuf;
                if (*ndp->ni_ptr == '/') {
                        vrele(dp);
                        while (*ndp->ni_ptr == '/') {
                                ndp->ni_ptr++;
                                ndp->ni_pathlen--;
                        }
                        dp = ndp->ni_rootdir;
                        VREF(dp);
                }
                ndp->ni_startdir = dp;
                if (error = lookup(ndp, p)) {
                        FREE(ndp->ni_pnbuf, M_NAMEI);
                        return (error);
                }
                /*
                 * Check for symbolic link
                 */
                if (ndp->ni_more == 0) {
                        if ((ndp->ni_nameiop & (SAVENAME | SAVESTART)) == 0)
                                FREE(ndp->ni_pnbuf, M_NAMEI);
                        else
                                ndp->ni_nameiop |= HASBUF;
                        return (0);
                }
                if ((ndp->ni_nameiop & LOCKPARENT) && ndp->ni_pathlen == 1)
                        VOP_UNLOCK(ndp->ni_dvp);
                if (ndp->ni_loopcnt++ >= MAXSYMLINKS) {
                        error = ELOOP;
                        break;
                }
                if (ndp->ni_pathlen > 1)
                        MALLOC(cp, char *, MAXPATHLEN, M_NAMEI, M_WAITOK);
                else
                        cp = ndp->ni_pnbuf;
                aiov.iov_base = cp;
                aiov.iov_len = MAXPATHLEN;
                auio.uio_iov = &aiov;
                auio.uio_iovcnt = 1;
                auio.uio_offset = 0;
                auio.uio_rw = UIO_READ;
                auio.uio_segflg = UIO_SYSSPACE;
                auio.uio_procp = (struct proc *)0;
                auio.uio_resid = MAXPATHLEN;
                if (error = VOP_READLINK(ndp->ni_vp, &auio, p->p_ucred)) {
                        if (ndp->ni_pathlen > 1)
                                free(cp, M_NAMEI);
                        break;
                }
                linklen = MAXPATHLEN - auio.uio_resid;
                if (linklen + ndp->ni_pathlen >= MAXPATHLEN) {
                        if (ndp->ni_pathlen > 1)
                                free(cp, M_NAMEI);
                        error = ENAMETOOLONG;
                        break;
                }
                if (ndp->ni_pathlen > 1) {
                        bcopy(ndp->ni_next, cp + linklen, ndp->ni_pathlen);
                        FREE(ndp->ni_pnbuf, M_NAMEI);
                        ndp->ni_pnbuf = cp;
                } else
                        ndp->ni_pnbuf[linklen] = '\0';
                ndp->ni_pathlen += linklen;
                vput(ndp->ni_vp);
                dp = ndp->ni_dvp;
        }
        FREE(ndp->ni_pnbuf, M_NAMEI);
        vrele(ndp->ni_dvp);
        vput(ndp->ni_vp);
        ndp->ni_vp = NULL;
        return (error);
}

/*
 * Search a pathname.
 * This is a very central and rather complicated routine.
 *
 * The pathname is pointed to by ni_ptr and is of length ni_pathlen.
 * The starting directory is taken from ni_startdir. The pathname is
 * descended until done, or a symbolic link is encountered. The variable
 * ni_more is clear if the path is completed; it is set to one if a
 * symbolic link needing interpretation is encountered.
 *
 * The flag argument is LOOKUP, CREATE, RENAME, or DELETE depending on
 * whether the name is to be looked up, created, renamed, or deleted.
 * When CREATE, RENAME, or DELETE is specified, information usable in
 * creating, renaming, or deleting a directory entry may be calculated.
 * If flag has LOCKPARENT or'ed into it, the parent directory is returned
 * locked. If flag has WANTPARENT or'ed into it, the parent directory is
 * returned unlocked. Otherwise the parent directory is not returned. If
 * the target of the pathname exists and LOCKLEAF is or'ed into the flag
 * the target is returned locked, otherwise it is returned unlocked.
 * When creating or renaming and LOCKPARENT is specified, the target may not
 * be ".".  When deleting and LOCKPARENT is specified, the target may be ".".
 * NOTE: (LOOKUP | LOCKPARENT) currently returns the parent vnode unlocked.
 *
 * Overall outline of lookup:
 *
 * dirloop:
 *      identify next component of name at ndp->ni_ptr
 *      handle degenerate case where name is null string
 *      if .. and crossing mount points and on mounted filesys, find parent
 *      call VOP_LOOKUP routine for next component name
 *          directory vnode returned in ni_dvp, unlocked unless LOCKPARENT set
 *          component vnode returned in ni_vp (if it exists), locked.
 *      if result vnode is mounted on and crossing mount points,
 *          find mounted on vnode
 *      if more components of name, do next level at dirloop
 *      return the answer in ni_vp, locked if LOCKLEAF set
 *          if LOCKPARENT set, return locked parent in ni_dvp
 *          if WANTPARENT set, return unlocked parent in ni_dvp
 */
lookup(ndp, p)
        register struct nameidata *ndp;
        struct proc *p;
{
        register char *cp;              /* pointer into pathname argument */
        register struct vnode *dp = 0;  /* the directory we are searching */
        struct vnode *tdp;              /* saved dp */
        struct mount *mp;               /* mount table entry */
        int docache;                    /* == 0 do not cache last component */
        int flag;                       /* LOOKUP, CREATE, RENAME or DELETE */
        int wantparent;                 /* 1 => wantparent or lockparent flag */
        int rdonly;                     /* mounted read-only flag bit(s) */
        int error = 0;

        /*
         * Setup: break out flag bits into variables.
         */
        flag = ndp->ni_nameiop & OPMASK;
        wantparent = ndp->ni_nameiop & (LOCKPARENT|WANTPARENT);
        docache = (ndp->ni_nameiop & NOCACHE) ^ NOCACHE;
        if (flag == DELETE || (wantparent && flag != CREATE))
                docache = 0;
        rdonly = MNT_RDONLY;
        if (ndp->ni_nameiop & REMOTE)
                rdonly |= MNT_EXRDONLY;
        ndp->ni_dvp = NULL;
        ndp->ni_more = 0;
        dp = ndp->ni_startdir;
        ndp->ni_startdir = NULLVP;
        VOP_LOCK(dp);

dirloop:
        /*
         * Search a new directory.
         *
         * The ni_hash value is for use by vfs_cache.
         * The last component of the filename is left accessible via
         * ndp->ptr for callers that need the name. Callers needing
         * the name set the SAVENAME flag. When done, they assume
         * responsibility for freeing the pathname buffer.
         */
        ndp->ni_hash = 0;
        for (cp = ndp->ni_ptr; *cp != 0 && *cp != '/'; cp++)
                ndp->ni_hash += (unsigned char)*cp;
        ndp->ni_namelen = cp - ndp->ni_ptr;
        if (ndp->ni_namelen >= NAME_MAX) {
                error = ENAMETOOLONG;
                goto bad;
        }
#ifdef NAMEI_DIAGNOSTIC
        { char c = *cp;
        *cp = '\0';
        printf("{%s}: ", ndp->ni_ptr);
        *cp = c; }
#endif
        ndp->ni_pathlen -= ndp->ni_namelen;
        ndp->ni_next = cp;
        ndp->ni_makeentry = 1;
        if (*cp == '\0' && docache == 0)
                ndp->ni_makeentry = 0;
        ndp->ni_isdotdot = (ndp->ni_namelen == 2 &&
                ndp->ni_ptr[1] == '.' && ndp->ni_ptr[0] == '.');

        /*
         * Check for degenerate name (e.g. / or "")
         * which is a way of talking about a directory,
         * e.g. like "/." or ".".
         */
        if (ndp->ni_ptr[0] == '\0') {
                if (flag != LOOKUP || wantparent) {
                        error = EISDIR;
                        goto bad;
                }
                if (dp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto bad;
                }
                if (!(ndp->ni_nameiop & LOCKLEAF))
                        VOP_UNLOCK(dp);
                ndp->ni_vp = dp;
                if (ndp->ni_nameiop & SAVESTART)
                        panic("lookup: SAVESTART");
                return (0);
        }

        /*
         * Handle "..": two special cases.
         * 1. If at root directory (e.g. after chroot)
         *    then ignore it so can't get out.
         * 2. If this vnode is the root of a mounted
         *    filesystem, then replace it with the
         *    vnode which was mounted on so we take the
         *    .. in the other file system.
         */
        if (ndp->ni_isdotdot) {
                for (;;) {
/* 17 Aug 92*/          if ((dp == ndp->ni_rootdir) || (dp == rootdir)) {
                                ndp->ni_dvp = dp;
                                ndp->ni_vp = dp;
                                VREF(dp);
                                goto nextname;
                        }
                        if ((dp->v_flag & VROOT) == 0 ||
                            (ndp->ni_nameiop & NOCROSSMOUNT))
                                break;
                        tdp = dp;
                        dp = dp->v_mount->mnt_vnodecovered;
                        vput(tdp);
                        VREF(dp);
                        VOP_LOCK(dp);
                }
        }

        /*
         * We now have a segment name to search for, and a directory to search.
         */
        if (error = VOP_LOOKUP(dp, ndp, p)) {
#ifdef DIAGNOSTIC
                if (ndp->ni_vp != NULL)
                        panic("leaf should be empty");
#endif
#ifdef NAMEI_DIAGNOSTIC
                printf("not found\n");
#endif
                if (flag == LOOKUP || flag == DELETE ||
                    error != ENOENT || *cp != 0)
                        goto bad;
                /*
                 * If creating and at end of pathname, then can consider
                 * allowing file to be created.
                 */
                if (ndp->ni_dvp->v_mount->mnt_flag & rdonly) {
                        error = EROFS;
                        goto bad;
                }
                /*
                 * We return with ni_vp NULL to indicate that the entry
                 * doesn't currently exist, leaving a pointer to the
                 * (possibly locked) directory inode in ndp->ni_dvp.
                 */
                if (ndp->ni_nameiop & SAVESTART) {
                        ndp->ni_startdir = ndp->ni_dvp;
                        VREF(ndp->ni_startdir);
                }
                return (0);
        }
#ifdef NAMEI_DIAGNOSTIC
        printf("found\n");
#endif

        dp = ndp->ni_vp;
        /*
         * Check for symbolic link
         */
        if ((dp->v_type == VLNK) &&
            ((ndp->ni_nameiop & FOLLOW) || *ndp->ni_next == '/')) {
                ndp->ni_more = 1;
                return (0);
        }

        /*
         * Check to see if the vnode has been mounted on;
         * if so find the root of the mounted file system.
         */
mntloop:
        while (dp->v_type == VDIR && (mp = dp->v_mountedhere) &&
               (ndp->ni_nameiop & NOCROSSMOUNT) == 0) {
                while(mp->mnt_flag & MNT_MLOCK) {
                        mp->mnt_flag |= MNT_MWAIT;
                        sleep((caddr_t)mp, PVFS);
                        goto mntloop;
                }
                if (error = VFS_ROOT(dp->v_mountedhere, &tdp))
                        goto bad2;
                vput(dp);
                ndp->ni_vp = dp = tdp;
        }

nextname:
        /*
         * Not a symbolic link.  If more pathname,
         * continue at next component, else return.
         */
        if (*ndp->ni_next == '/') {
                ndp->ni_ptr = ndp->ni_next;
                while (*ndp->ni_ptr == '/') {
                        ndp->ni_ptr++;
                        ndp->ni_pathlen--;
                }
                vrele(ndp->ni_dvp);
                goto dirloop;
        }
        /*
         * Check for read-only file systems.
         */
        if (flag == DELETE || flag == RENAME) {
                /*
                 * Disallow directory write attempts on read-only
                 * file systems.
                 */
                if ((dp->v_mount->mnt_flag & rdonly) ||
                    (wantparent && (ndp->ni_dvp->v_mount->mnt_flag & rdonly))) {
                        error = EROFS;
                        goto bad2;
                }
        }
        if (ndp->ni_nameiop & SAVESTART) {
                ndp->ni_startdir = ndp->ni_dvp;
                VREF(ndp->ni_startdir);
        }
        if (!wantparent)
                vrele(ndp->ni_dvp);
        if ((ndp->ni_nameiop & LOCKLEAF) == 0)
                VOP_UNLOCK(dp);
        return (0);

bad2:
        if ((ndp->ni_nameiop & LOCKPARENT) && *ndp->ni_next == '\0')
                VOP_UNLOCK(ndp->ni_dvp);
        vrele(ndp->ni_dvp);
bad:
        vput(dp);
        ndp->ni_vp = NULL;
        return (error);
}