Re: [PATCH v13 07/11] LSM: Helpers for attribute names and filling lsm_ctx

John Johansen
2023-08-10T15:57:13Z

On 8/2/23 10:44, 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.
>
> Both are used in module specific components of LSM system calls.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
Reviewed-by: John Johansen <john.johansen@canonical.com>

> ---
> include/linux/security.h | 14 ++++++++++++++
> security/lsm_syscalls.c | 24 +++++++++++++++++++++++
> security/security.c | 41 ++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 79 insertions(+)
>
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 0d882cb221f4..817cf28dbf8a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -32,6 +32,7 @@
> #include <linux/string.h>
> #include <linux/mm.h>
> #include <linux/sockptr.h>
> +#include <uapi/linux/lsm.h>
>
> struct linux_binprm;
> struct cred;
> @@ -263,6 +264,7 @@ int unregister_blocking_lsm_notifier(struct notifier_block *nb);
> /* prototypes */
> extern int security_init(void);
> extern int early_security_init(void);
> +extern u64 lsm_name_to_attr(const char *name);
>
> /* Security operations */
> int security_binder_set_context_mgr(const struct cred *mgr);
> @@ -488,6 +490,8 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
> int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
> int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
> int security_locked_down(enum lockdown_reason what);
> +int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
> + size_t context_size, u64 id, u64 flags);
> #else /* CONFIG_SECURITY */
>
> static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
> @@ -505,6 +509,11 @@ static inline int unregister_blocking_lsm_notifier(struct notifier_block *nb)
> return 0;
> }
>
> +static inline u64 lsm_name_to_attr(const char *name)
> +{
> + return LSM_ATTR_UNDEF;
> +}
> +
> static inline void security_free_mnt_opts(void **mnt_opts)
> {
> }
> @@ -1408,6 +1417,11 @@ static inline int security_locked_down(enum lockdown_reason what)
> {
> return 0;
> }
> +static inline int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
> + size_t context_size, u64 id, u64 flags)
> +{
> + return -EOPNOTSUPP;
> +}
> #endif /* CONFIG_SECURITY */
>
> #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
> diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c
> index f03f2d17ab49..bc22f05e2d8c 100644
> --- a/security/lsm_syscalls.c
> +++ b/security/lsm_syscalls.c
> @@ -17,6 +17,30 @@
> #include <linux/lsm_hooks.h>
> #include <uapi/linux/lsm.h>
>
> +/**
> + * lsm_name_to_attr - map an LSM attribute name to its ID
> + * @name: name of the attribute
> + *
> + * Returns the LSM attribute value associated with @name, or 0 if
> + * there is no mapping.
> + */
> +u64 lsm_name_to_attr(const char *name)
> +{
> + if (!strcmp(name, "current"))
> + return LSM_ATTR_CURRENT;
> + if (!strcmp(name, "exec"))
> + return LSM_ATTR_EXEC;
> + if (!strcmp(name, "fscreate"))
> + return LSM_ATTR_FSCREATE;
> + if (!strcmp(name, "keycreate"))
> + return LSM_ATTR_KEYCREATE;
> + if (!strcmp(name, "prev"))
> + return LSM_ATTR_PREV;
> + if (!strcmp(name, "sockcreate"))
> + return LSM_ATTR_SOCKCREATE;
> + return LSM_ATTR_UNDEF;
> +}
> +
> /**
> * sys_lsm_set_self_attr - Set current task's security module attribute
> * @attr: which attribute to set
> diff --git a/security/security.c b/security/security.c
> index cde7f3a13e7c..f1038686ebd0 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -770,6 +770,47 @@ 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, -ENOMEM
> + * if memory can't be allocated.
> + */
> +int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
> + size_t context_size, u64 id, u64 flags)
> +{
> + struct lsm_ctx *lctx;
> + size_t locallen = struct_size(lctx, ctx, context_size);
> + int rc = 0;
> +
> + lctx = kzalloc(locallen, GFP_KERNEL);
> + if (lctx == NULL)
> + return -ENOMEM;
> +
> + lctx->id = id;
> + lctx->flags = flags;
> + lctx->ctx_len = context_size;
> + lctx->len = locallen;
> +
> + memcpy(lctx->ctx, context, context_size);
> +
> + if (copy_to_user(ctx, lctx, locallen))
> + rc = -EFAULT;
> +
> + kfree(lctx);
> +
> + return rc;
> +}
> +
> /*
> * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
> * can be accessed with: