On 5/22/22 13:31, Serge E. Hallyn wrote:
On Wed, Apr 20, 2022 at 10:06:18AM -0400, Stefan Berger wrote:
Define mac_admin_ns_capable() as a wrapper for the combined ns_capable()
checks on CAP_MAC_ADMIN and CAP_SYS_ADMIN in a user namespace. Return
true on the check if either capability or both are available.
Use mac_admin_ns_capable() in place of capable(SYS_ADMIN). This will allow
an IMA namespace to read the policy with only CAP_MAC_ADMIN, which has
less privileges than CAP_SYS_ADMIN.
Since CAP_MAC_ADMIN is an additional capability added to an existing gate
avoid auditing in case it is not set.
It would probably be best to become a user of
https://lore.kernel.org/all/20220217145003.78982-2-cgzones@xxxxxxxxxxxxxx/
when that lands.
Hm,I'll try to monitor to see when this gets merged. Though the function
proposed there uses a hard-coded init_user_ns, which may not work for
everyone.
Signed-off-by: Denis Semakin <denis.semakin@xxxxxxxxxx>
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
v11:
- use ns_capable_noaudit for CAP_MAC_ADMIN to avoid auditing in this case
---
include/linux/capability.h | 6 ++++++
security/integrity/ima/ima.h | 6 ++++++
security/integrity/ima/ima_fs.c | 5 ++++-
3 files changed, 16 insertions(+), 1 deletion(-)
diff --git a/include/linux/capability.h b/include/linux/capability.h
index 65efb74c3585..dc3e1230b365 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -270,6 +270,12 @@ static inline bool checkpoint_restore_ns_capable(struct user_namespace *ns)
ns_capable(ns, CAP_SYS_ADMIN);
}
+static inline bool mac_admin_ns_capable(struct user_namespace *ns)
+{
+ return ns_capable_noaudit(ns, CAP_MAC_ADMIN) ||
+ ns_capable(ns, CAP_SYS_ADMIN);
+}
+
/* audit system wants to get cap info from files as well */
int get_vfs_caps_from_disk(struct user_namespace *mnt_userns,
const struct dentry *dentry,
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 5bf7f080c2be..626a6ce2453c 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -491,4 +491,10 @@ static inline int ima_filter_rule_match(u32 secid, u32 field, u32 op,
#define POLICY_FILE_FLAGS S_IWUSR
#endif /* CONFIG_IMA_READ_POLICY */
+static inline
+struct user_namespace *ima_user_ns_from_file(const struct file *filp)
+{
+ return file_inode(filp)->i_sb->s_user_ns;
+}
include/linux/fs.h has file_mnt_user_ns(). Maybe you should add a
file_sb_user_ns() next to that?
I did that now:
+static inline
+struct user_namespace *ima_user_ns_from_file(struct file *filp)
+{
+ return file_sb_user_ns(filp);
+}
+
+static inline struct user_namespace *file_sb_user_ns(struct file *file)
+{
+ return i_user_ns(file_inode(file));
+}
+
+
#endif /* __LINUX_IMA_H */
diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 89d3113ceda1..c41aa61b7393 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -377,6 +377,9 @@ static const struct seq_operations ima_policy_seqops = {
*/
static int ima_open_policy(struct inode *inode, struct file *filp)
{
+#ifdef CONFIG_IMA_READ_POLICY
+ struct user_namespace *user_ns = ima_user_ns_from_file(filp);
+#endif
struct ima_namespace *ns = &init_ima_ns;
if (!(filp->f_flags & O_WRONLY)) {
@@ -385,7 +388,7 @@ static int ima_open_policy(struct inode *inode, struct file *filp)
#else
if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
return -EACCES;
- if (!capable(CAP_SYS_ADMIN))
+ if (!mac_admin_ns_capable(user_ns))
return -EPERM;
return seq_open(filp, &ima_policy_seqops);
#endif
--
2.34.1
