git: 4710439ec594 - releng/13.0 - mount: Disallow mounting over a jail root

[Mark Johnston]

The branch releng/13.0 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=4710439ec594a5375657acc403326f868d05a05a

commit 4710439ec594a5375657acc403326f868d05a05a
Author:     Mark Johnston <markj at FreeBSD.org>
AuthorDate: 2021-04-05 21:19:15 +0000
Commit:     Mark Johnston <markj at FreeBSD.org>
CommitDate: 2021-04-06 19:18:59 +0000

    mount: Disallow mounting over a jail root
    
    Discussed with: jamie
    Approved by:    re (so, implicit)
    Approved by:    so
    Security:       CVE-2020-25584
    Security:       FreeBSD-SA-21:10.jail_mount
    
    (cherry picked from commit 2425f5e9128102c8e6e473567ad6759a55be5b02)
    (cherry picked from commit 3ae17faa370491d7ce1fcfc4d5b9cd1ed0117b67)
---
 sys/kern/vfs_mount.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index b3870e46c5e9..59000728efcc 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -918,10 +918,10 @@ vfs_domount_first(
 
 	/*
 	 * If the jail of the calling thread lacks permission for this type of
-	 * file system, deny immediately.
+	 * file system, or is trying to cover its own root, deny immediately.
 	 */
-	if (jailed(td->td_ucred) && !prison_allow(td->td_ucred,
-	    vfsp->vfc_prison_flag)) {
+	if (jailed(td->td_ucred) && (!prison_allow(td->td_ucred,
+	    vfsp->vfc_prison_flag) || vp == td->td_ucred->cr_prison->pr_root)) {
 		vput(vp);
 		return (EPERM);
 	}