On Wed, Sep 6, 2023 at 7:48 PM Casey Schaufler [off-list ref] wrote:

On 9/6/2023 4:22 PM, Paul Moore wrote:

quoted

On Aug 28, 2023 Casey Schaufler [off-list ref] wrote:

quoted

Create a system call lsm_get_self_attr() to provide the security
module maintained attributes of the current process.
Create a system call lsm_set_self_attr() to set a security
module maintained attribute of the current process.
Historically these attributes have been exposed to user space via
entries in procfs under /proc/self/attr.

The attribute value is provided in a lsm_ctx structure. The structure
identifies the size of the attribute, and the attribute value. The format
of the attribute value is defined by the security module. A flags field
is included for LSM specific information. It is currently unused and must
be 0. The total size of the data, including the lsm_ctx structure and any
padding, is maintained as well.

struct lsm_ctx {
        __u64 id;
        __u64 flags;
        __u64 len;
        __u64 ctx_len;
        __u8 ctx[];
};

Two new LSM hooks are used to interface with the LSMs.
security_getselfattr() collects the lsm_ctx values from the
LSMs that support the hook, accounting for space requirements.
security_setselfattr() identifies which LSM the attribute is
intended for and passes it along.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <redacted>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>
---
 Documentation/userspace-api/lsm.rst |  70 +++++++++++++
 include/linux/lsm_hook_defs.h       |   4 +
 include/linux/lsm_hooks.h           |   1 +
 include/linux/security.h            |  19 ++++
 include/linux/syscalls.h            |   5 +
 include/uapi/linux/lsm.h            |  36 +++++++
 kernel/sys_ni.c                     |   2 +
 security/Makefile                   |   1 +
 security/lsm_syscalls.c             |  57 +++++++++++
 security/security.c                 | 146 ++++++++++++++++++++++++++++
 10 files changed, 341 insertions(+)
 create mode 100644 Documentation/userspace-api/lsm.rst
 create mode 100644 security/lsm_syscalls.c

..

quoted

diff --git a/security/security.c b/security/security.c
index 82253294069c..aa4ade1f71b9 100644
--- a/security/security.c
+++ b/security/security.c

@@ -3798,6 +3798,152 @@ void security_d_instantiate(struct dentry *dentry, struct inode *inode)
 }
 EXPORT_SYMBOL(security_d_instantiate);

+/**
+ * security_getselfattr - Read an LSM attribute of the current process.
+ * @attr: which attribute to return
+ * @uctx: the user-space destination for the information, or NULL
+ * @size: pointer to the size of space available to receive the data
+ * @flags: special handling options. LSM_FLAG_SINGLE indicates that only
+ * attributes associated with the LSM identified in the passed @ctx be
+ * reported.
+ *
+ * A NULL value for @uctx can be used to get both the number of attributes
+ * and the size of the data.
+ *
+ * Returns the number of attributes found on success, negative value
+ * on error. @size is reset to the total size of the data.
+ * If @size is insufficient to contain the data -E2BIG is returned.
+ */
+int security_getselfattr(unsigned int attr, struct lsm_ctx __user *uctx,
+                     size_t __user *size, u32 flags)
+{
+    struct security_hook_list *hp;
+    struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, };
+    u8 __user *base = (u8 __user *)uctx;
+    size_t total = 0;
+    size_t entrysize;
+    size_t left;
+    bool toobig = false;
+    bool single = false;
+    int count = 0;
+    int rc;
+
+    if (attr == LSM_ATTR_UNDEF)
+            return -EINVAL;
+    if (size == NULL)
+            return -EINVAL;
+    if (get_user(left, size))
+            return -EFAULT;
+
+    if (flags) {
+            /*
+             * Only flag supported is LSM_FLAG_SINGLE
+             */
+            if (flags & LSM_FLAG_SINGLE)
+                    return -EINVAL;

Should this be something like the following?

  if (flags & ~LSM_FLAG_SINGLE)
    return -EINVAL;

Yes. I have a fix ready. There are a couple other touch-ups, too.

Great.  Since you are doing another revision, can you double check all
of the patch subject lines to ensure you don't have any double spaces?
 I see at least one, possibly two more.

-- 
paul-moore.com