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Allow realpath to work for file mounts

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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
This commit is contained in:
Doug Rabson 2022-12-04 15:53:07 +00:00
parent 521fbb722c
commit a1d74b2dab
2 changed files with 31 additions and 2 deletions
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28
sys/kern/vfs_cache.c
View file

@ -3147,12 +3147,36 @@ kern___realpathat(struct thread *td, int fd, const char *path, char *buf,
pathseg, path, fd, &cap_fstat_rights);
if ((error = namei(&nd)) != 0)
return (error);
error = vn_fullpath_hardlink(nd.ni_vp, nd.ni_dvp, nd.ni_cnd.cn_nameptr,
nd.ni_cnd.cn_namelen, &retbuf, &freebuf, &size);
if (nd.ni_vp->v_type == VREG && nd.ni_dvp->v_type != VDIR &&
(nd.ni_vp->v_vflag & VV_ROOT) != 0) {
/*
* This happens if vp is a file mount. The call to
* vn_fullpath_hardlink can panic if path resolution can't be
* handled without the directory.
*
* To resolve this, we find the vnode which was mounted on -
* this should have a unique global path since we disallow
* mounting on linked files.
*/
struct vnode *covered_vp;
error = vn_lock(nd.ni_vp, LK_SHARED);
if (error != 0)
goto out;
covered_vp = nd.ni_vp->v_mount->mnt_vnodecovered;
vref(covered_vp);
VOP_UNLOCK(nd.ni_vp);
error = vn_fullpath(covered_vp, &retbuf, &freebuf);
vrele(covered_vp);
} else {
error = vn_fullpath_hardlink(nd.ni_vp, nd.ni_dvp, nd.ni_cnd.cn_nameptr,
nd.ni_cnd.cn_namelen, &retbuf, &freebuf, &size);
}
if (error == 0) {
error = copyout(retbuf, buf, size);
free(freebuf, M_TEMP);
}
out:
vrele(nd.ni_vp);
vrele(nd.ni_dvp);
NDFREE_PNBUF(&nd);

5
sys/kern/vfs_mount.c
View file

@ -1108,6 +1108,11 @@ vfs_domount_first(
if (vfsp->vfc_flags & VFCF_FILEMOUNT) {
if (error == 0 && vp->v_type != VDIR && vp->v_type != VREG)
error = EINVAL;
/*
* For file mounts, ensure that there is only one hardlink to the file.
*/
if (error == 0 && vp->v_type == VREG && va.va_nlink != 1)
error = EINVAL;
} else {
if (error == 0 && vp->v_type != VDIR)
error = ENOTDIR;