/* $OpenBSD: vfs_getcwd.c,v 1.38 2022/12/05 23:18:37 deraadt Exp $ */
/* $NetBSD: vfs_getcwd.c,v 1.3.2.3 1999/07/11 10:24:09 sommerfeld Exp $ */

/*
 * Copyright (c) 1999 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Bill Sommerfeld.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/namei.h>
#include <sys/filedesc.h>
#include <sys/stat.h>
#include <sys/lock.h>
#include <sys/vnode.h>
#include <sys/mount.h>
#include <sys/ktrace.h>
#include <sys/proc.h>
#include <sys/uio.h>
#include <sys/malloc.h>
#include <sys/dirent.h>
#include <ufs/ufs/dir.h>        /* only for DIRBLKSIZ */

#include <sys/syscallargs.h>


/* Find parent vnode of *lvpp, return in *uvpp */
int
vfs_getcwd_scandir(struct vnode **lvpp, struct vnode **uvpp, char **bpp,
    char *bufp, struct proc *p)
{
        int eofflag, tries, dirbuflen = 0, len, reclen, error = 0;
        off_t off;
        struct uio uio;
        struct iovec iov;
        char *dirbuf = NULL;
        ino_t fileno;
        struct vattr va;
        struct vnode *uvp = NULL;
        struct vnode *lvp = *lvpp;
        struct componentname cn;

        tries = 0;

        /*
         * If we want the filename, get some info we need while the
         * current directory is still locked.
         */
        if (bufp != NULL) {
                error = VOP_GETATTR(lvp, &va, p->p_ucred, p);
                if (error) {
                        vput(lvp);
                        *lvpp = NULL;
                        *uvpp = NULL;
                        return (error);
                }
        }

        cn.cn_nameiop = LOOKUP;
        cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
        cn.cn_proc = p;
        cn.cn_cred = p->p_ucred;
        cn.cn_pnbuf = NULL;
        cn.cn_nameptr = "..";
        cn.cn_namelen = 2;
        cn.cn_consume = 0;

        /* Get parent vnode using lookup of '..' */
        error = VOP_LOOKUP(lvp, uvpp, &cn);
        if (error) {
                vput(lvp);
                *lvpp = NULL;
                *uvpp = NULL;
                return (error);
        }

        uvp = *uvpp;

        /* If we don't care about the pathname, we're done */
        if (bufp == NULL) {
                error = 0;
                goto out;
        }

        fileno = va.va_fileid;

        dirbuflen = DIRBLKSIZ;
        if (dirbuflen < va.va_blocksize)
                dirbuflen = va.va_blocksize;
        /* XXX we need some limit for fuse, 1 MB should be enough */
        if (dirbuflen > 0xfffff) {
                error = EINVAL;
                goto out;
        }
        dirbuf = malloc(dirbuflen, M_TEMP, M_WAITOK);

        off = 0;

        do {
                char   *cpos;
                struct dirent *dp;

                iov.iov_base = dirbuf;
                iov.iov_len = dirbuflen;

                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                uio.uio_offset = off;
                uio.uio_resid = dirbuflen;
                uio.uio_segflg = UIO_SYSSPACE;
                uio.uio_rw = UIO_READ;
                uio.uio_procp = p;

                eofflag = 0;

                /* Call VOP_READDIR of parent */
                error = VOP_READDIR(uvp, &uio, p->p_ucred, &eofflag);

                off = uio.uio_offset;

                /* Try again if NFS tosses its cookies */
                if (error == EINVAL && tries < 3) {
                        tries++;
                        off = 0;
                        continue;
                } else if (error) {
                        goto out; /* Old userland getcwd() behaviour */
                }

                cpos = dirbuf;
                tries = 0;

                /* Scan directory page looking for matching vnode */ 
                for (len = (dirbuflen - uio.uio_resid); len > 0;
                     len -= reclen) {
                        dp = (struct dirent *)cpos;
                        reclen = dp->d_reclen;

                        /* Check for malformed directory */
                        if (reclen < DIRENT_RECSIZE(1) || reclen > len) {
                                error = EINVAL;
                                goto out;
                        }

                        if (dp->d_fileno == fileno) {
                                char *bp = *bpp;

                                if (offsetof(struct dirent, d_name) +
                                    dp->d_namlen > reclen) {
                                        error = EINVAL;
                                        goto out;
                                }
                                bp -= dp->d_namlen;
                                if (bp <= bufp) {
                                        error = ERANGE;
                                        goto out;
                                }

                                memmove(bp, dp->d_name, dp->d_namlen);
                                error = 0;
                                *bpp = bp;

                                goto out;
                        }

                        cpos += reclen;
                }

        } while (!eofflag);

        error = ENOENT;

out:

        vrele(lvp);
        *lvpp = NULL;

        free(dirbuf, M_TEMP, dirbuflen);

        return (error);
}

/* Do a lookup in the vnode-to-name reverse */
int
vfs_getcwd_getcache(struct vnode **lvpp, struct vnode **uvpp, char **bpp,
    char *bufp)
{
        struct vnode *lvp, *uvp = NULL;
        char *obp;
        int error, vpid;

        lvp = *lvpp;
        obp = *bpp;     /* Save original position to restore to on error */

        error = cache_revlookup(lvp, uvpp, bpp, bufp);
        if (error) {
                if (error != -1) {
                        vput(lvp);
                        *lvpp = NULL;
                        *uvpp = NULL;
                }

                return (error);
        }

        uvp = *uvpp;
        vpid = uvp->v_id;


        /* Release current lock before acquiring the parent lock */
        VOP_UNLOCK(lvp);

        error = vget(uvp, LK_EXCLUSIVE | LK_RETRY);
        if (error)
                *uvpp = NULL;

        /*
         * Verify that vget() succeeded, and check that vnode capability
         * didn't change while we were waiting for the lock.
         */
        if (error || (vpid != uvp->v_id)) {
                /*
                 * Try to get our lock back. If that works, tell the caller to
                 * try things the hard way, otherwise give up.
                 */
                if (!error)
                        vput(uvp);

                *uvpp = NULL;

                error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
                if (!error) {
                        *bpp = obp; /* restore the buffer */
                        return (-1);
                }
        }

        vrele(lvp);
        *lvpp = NULL;

        return (error);
}

/* Common routine shared by sys___getcwd() and vn_isunder() and sys___realpath() */
int
vfs_getcwd_common(struct vnode *lvp, struct vnode *rvp, char **bpp, char *bufp,
    int limit, int flags, struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct vnode *uvp = NULL;
        char *bp = NULL;
        int error, perms = VEXEC;

        if (rvp == NULL) {
                rvp = fdp->fd_rdir;
                if (rvp == NULL)
                        rvp = rootvnode;
        }

        vref(rvp);
        vref(lvp);

        error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
        if (error) {
                vrele(lvp);
                lvp = NULL;
                goto out;
        }

        if (bufp)
                bp = *bpp;

        if (lvp == rvp) {
                if (bp)
                        *(--bp) = '/';
                goto out;
        }

        /*
         * This loop will terminate when we hit the root, VOP_READDIR() or
         * VOP_LOOKUP() fails, or we run out of space in the user buffer.
         */
        do {
                if (lvp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto out;
                }

                /* Check for access if caller cares */
                if (flags & GETCWD_CHECK_ACCESS) {
                        error = VOP_ACCESS(lvp, perms, p->p_ucred, p);
                        if (error)
                                goto out;
                        perms = VEXEC|VREAD;
                }

                /* Step up if we're a covered vnode */
                while (lvp->v_flag & VROOT) {
                        struct vnode *tvp;

                        if (lvp == rvp)
                                goto out;

                        tvp = lvp;
                        lvp = lvp->v_mount->mnt_vnodecovered;

                        vput(tvp);

                        if (lvp == NULL) {
                                error = ENOENT;
                                goto out;
                        }

                        vref(lvp);

                        error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY);
                        if (error) {
                                vrele(lvp);
                                lvp = NULL;
                                goto out;
                        }
                }

                /* Look in the name cache */
                error = vfs_getcwd_getcache(&lvp, &uvp, &bp, bufp);

                if (error == -1) {
                        /* If that fails, look in the directory */
                        error = vfs_getcwd_scandir(&lvp, &uvp, &bp, bufp, p);
                }

                if (error)
                        goto out;

#ifdef DIAGNOSTIC
                if (lvp != NULL)
                        panic("getcwd: oops, forgot to null lvp");
                if (bufp && (bp <= bufp)) {
                        panic("getcwd: oops, went back too far");
                }
#endif

                if (bp)
                        *(--bp) = '/';

                lvp = uvp;
                uvp = NULL;
                limit--;

        } while ((lvp != rvp) && (limit > 0)); 

out:

        if (bpp)
                *bpp = bp;

        if (uvp)
                vput(uvp);

        if (lvp)
                vput(lvp);

        vrele(rvp);

        return (error);
}

/* Find pathname of a process's current directory */
int
sys___getcwd(struct proc *p, void *v, register_t *retval) 
{
        struct sys___getcwd_args *uap = v;
        int error, len = SCARG(uap, len);
        char *path, *bp;

        if (len > MAXPATHLEN * 4)
                len = MAXPATHLEN * 4;
        else if (len < 2)
                return (ERANGE);

        path = malloc(len, M_TEMP, M_WAITOK);

        bp = &path[len - 1];
        *bp = '\0';

        /*
         * 5th argument here is "max number of vnodes to traverse".
         * Since each entry takes up at least 2 bytes in the output
         * buffer, limit it to N/2 vnodes for an N byte buffer.
         */
        error = vfs_getcwd_common(p->p_fd->fd_cdir, NULL, &bp, path, len/2,
            GETCWD_CHECK_ACCESS, p);

        if (error)
                goto out;

        /* Put the result into user buffer */
        error = copyoutstr(bp, SCARG(uap, buf), MAXPATHLEN, NULL);

#ifdef KTRACE
        if (KTRPOINT(p, KTR_NAMEI))
                ktrnamei(p, bp);
#endif

out:
        free(path, M_TEMP, len);

        return (error);
}