linux-kernel - [PATCH 4.14 45/95] Revert 95ebabde382c ("capabilities: Dont allow writing ambiguous v3 file capabilities")

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Date:   Mon, 15 Mar 2021 14:57:15 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 4.14 45/95] Revert 95ebabde382c ("capabilities: Dont allow writing ambiguous v3 file capabilities")

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Eric W. Biederman <ebiederm@...ssion.com>

commit 3b0c2d3eaa83da259d7726192cf55a137769012f upstream.

It turns out that there are in fact userspace implementations that
care and this recent change caused a regression.

https://github.com/containers/buildah/issues/3071

As the motivation for the original change was future development,
and the impact is existing real world code just revert this change
and allow the ambiguity in v3 file caps.

Cc: stable@...r.kernel.org
Fixes: 95ebabde382c ("capabilities: Don't allow writing ambiguous v3 file capabilities")
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 security/commoncap.c |   12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -507,8 +507,7 @@ int cap_convert_nscap(struct dentry *den
 	__u32 magic, nsmagic;
 	struct inode *inode = d_backing_inode(dentry);
 	struct user_namespace *task_ns = current_user_ns(),
-		*fs_ns = inode->i_sb->s_user_ns,
-		*ancestor;
+		*fs_ns = inode->i_sb->s_user_ns;
 	kuid_t rootid;
 	size_t newsize;
 
@@ -531,15 +530,6 @@ int cap_convert_nscap(struct dentry *den
 	if (nsrootid == -1)
 		return -EINVAL;
 
-	/*
-	 * Do not allow allow adding a v3 filesystem capability xattr
-	 * if the rootid field is ambiguous.
-	 */
-	for (ancestor = task_ns->parent; ancestor; ancestor = ancestor->parent) {
-		if (from_kuid(ancestor, rootid) == 0)
-			return -EINVAL;
-	}
-
 	newsize = sizeof(struct vfs_ns_cap_data);
 	nscap = kmalloc(newsize, GFP_ATOMIC);
 	if (!nscap)