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.
Signed-off-by: Denis Semakin <[email protected]>
Signed-off-by: Stefan Berger <[email protected]>
---
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;
+}
+
#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
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/[email protected]/
>
> 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 <[email protected]>
>> Signed-off-by: Stefan Berger <[email protected]>
>>
>> ---
>> 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