On 03/04/2023 20:03, Casey Schaufler wrote:
On 4/3/2023 2:47 AM, Mickaël Salaün wrote:
On 15/03/2023 23:47, Casey Schaufler wrote:
Add lsm_name_to_attr(), which translates a text string to a
LSM_ATTR value if one is available.
Add lsm_fill_user_ctx(), which fills a struct lsm_ctx, including
the trailing attribute value.
All are used in module specific components of LSM system calls.
Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
include/linux/security.h | 13 ++++++++++
security/lsm_syscalls.c | 51 ++++++++++++++++++++++++++++++++++++++++
security/security.c | 31 ++++++++++++++++++++++++
3 files changed, 95 insertions(+)
[...]
diff --git a/security/security.c b/security/security.c
index 2c57fe28c4f7..f7b814a3940c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -753,6 +753,37 @@ static int lsm_superblock_alloc(struct
super_block *sb)
return 0;
}
+/**
+ * lsm_fill_user_ctx - Fill a user space lsm_ctx structure
+ * @ctx: an LSM context to be filled
+ * @context: the new context value
+ * @context_size: the size of the new context value
+ * @id: LSM id
+ * @flags: LSM defined flags
+ *
+ * Fill all of the fields in a user space lsm_ctx structure.
+ * Caller is assumed to have verified that @ctx has enough space
+ * for @context.
+ * Returns 0 on success, -EFAULT on a copyout error.
+ */
+int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
+ size_t context_size, u64 id, u64 flags)
+{
+ struct lsm_ctx local;
+ void __user *vc = ctx;
+
+ local.id = id;
+ local.flags = flags;
+ local.ctx_len = context_size;
+ local.len = context_size + sizeof(local);
+ vc += sizeof(local);
+ if (copy_to_user(ctx, &local, sizeof(local)))
+ return -EFAULT;
+ if (context_size > 0 && copy_to_user(vc, context, context_size))
+ return -EFAULT;
Can we do a single copy_to_user() call?
It would be possible, but would require allocating memory and copying
the context. I don't see that as an improvement.
That would avoid inconsistent user space data, could speed up a bit
the operation, and make the code easier to understand. To use the
stack, we need to know the maximum size of context_size for all use
cases, which seems reasonable and can be checked at build time (on
each LSM side, and potentially with specific context type passed as
enum instead of context_size) and run time (for this generic helper).
Knowning the maximum size of attributes for all LSMs and hard coding
that here would make maintaining this code really painful.
Hmm, I forgot about variable-length strings, but maybe a reasonable
common maximum size (that could fit on the stack) could be found?
+ return 0;
+}
+
/*
* The default value of the LSM hook is defined in
linux/lsm_hook_defs.h and
* can be accessed with:
