From 9060e01f5c9c30813696a5f76f521c3b040c4e07 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Thu, 17 Dec 2020 09:42:00 -0600 Subject: capabilities: Don't allow writing ambiguous v3 file capabilities [ Upstream commit 95ebabde382c371572297915b104e55403674e73 ] The v3 file capabilities have a uid field that records the filesystem uid of the root user of the user namespace the file capabilities are valid in. When someone is silly enough to have the same underlying uid as the root uid of multiple nested containers a v3 filesystem capability can be ambiguous. In the spirit of don't do that then, forbid writing a v3 filesystem capability if it is ambiguous. Fixes: 8db6c34f1dbc ("Introduce v3 namespaced file capabilities") Reviewed-by: Andrew G. Morgan Reviewed-by: Serge Hallyn Signed-off-by: Eric W. Biederman Signed-off-by: Sasha Levin --- security/commoncap.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'security') diff --git a/security/commoncap.c b/security/commoncap.c index a1dee0ab345a..1bc40e78fa7f 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -506,7 +506,8 @@ int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size) __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; + *fs_ns = inode->i_sb->s_user_ns, + *ancestor; kuid_t rootid; size_t newsize; @@ -529,6 +530,15 @@ int cap_convert_nscap(struct dentry *dentry, void **ivalue, size_t size) 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) -- cgit v1.2.3