Allow realpath to work for file mounts
For file mounts, the directory vnode is not available from namei and this prevents the use of vn_fullpath_hardlink. In this case, we can use the vnode which was covered by the file mount with vn_fullpath. This also disallows file mounts over files with link counts greater than one to ensure a deterministic path to the mount point. Reviewed by: mjg, kib Tested by: pho
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@ -3147,12 +3147,36 @@ kern___realpathat(struct thread *td, int fd, const char *path, char *buf,
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pathseg, path, fd, &cap_fstat_rights);
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if ((error = namei(&nd)) != 0)
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return (error);
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error = vn_fullpath_hardlink(nd.ni_vp, nd.ni_dvp, nd.ni_cnd.cn_nameptr,
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nd.ni_cnd.cn_namelen, &retbuf, &freebuf, &size);
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if (nd.ni_vp->v_type == VREG && nd.ni_dvp->v_type != VDIR &&
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(nd.ni_vp->v_vflag & VV_ROOT) != 0) {
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/*
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* This happens if vp is a file mount. The call to
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* vn_fullpath_hardlink can panic if path resolution can't be
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* handled without the directory.
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*
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* To resolve this, we find the vnode which was mounted on -
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* this should have a unique global path since we disallow
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* mounting on linked files.
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*/
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struct vnode *covered_vp;
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error = vn_lock(nd.ni_vp, LK_SHARED);
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if (error != 0)
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goto out;
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covered_vp = nd.ni_vp->v_mount->mnt_vnodecovered;
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vref(covered_vp);
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VOP_UNLOCK(nd.ni_vp);
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error = vn_fullpath(covered_vp, &retbuf, &freebuf);
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vrele(covered_vp);
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} else {
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error = vn_fullpath_hardlink(nd.ni_vp, nd.ni_dvp, nd.ni_cnd.cn_nameptr,
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nd.ni_cnd.cn_namelen, &retbuf, &freebuf, &size);
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}
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if (error == 0) {
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error = copyout(retbuf, buf, size);
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free(freebuf, M_TEMP);
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}
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out:
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vrele(nd.ni_vp);
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vrele(nd.ni_dvp);
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NDFREE_PNBUF(&nd);
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@ -1108,6 +1108,11 @@ vfs_domount_first(
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if (vfsp->vfc_flags & VFCF_FILEMOUNT) {
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if (error == 0 && vp->v_type != VDIR && vp->v_type != VREG)
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error = EINVAL;
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/*
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* For file mounts, ensure that there is only one hardlink to the file.
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*/
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if (error == 0 && vp->v_type == VREG && va.va_nlink != 1)
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error = EINVAL;
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} else {
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if (error == 0 && vp->v_type != VDIR)
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error = ENOTDIR;
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