From: Eric W. Biederman Date: Thu, 17 Dec 2020 15:42:00 +0000 (-0600) Subject: capabilities: Don't allow writing ambiguous v3 file capabilities X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=95ebabde382c371572297915b104e55403674e73;p=linux.git capabilities: Don't allow writing ambiguous v3 file capabilities 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 --- diff --git a/security/commoncap.c b/security/commoncap.c index bacc1111d871b..74b9cc8cef34a 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -481,7 +481,8 @@ int cap_convert_nscap(struct dentry *dentry, const 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; @@ -504,6 +505,15 @@ int cap_convert_nscap(struct dentry *dentry, const 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)