Re: [PATCH v9 09/11] AppArmor: Add selfattr hooks

Kees Cook
2023-04-21T19:54:34Z

On Fri, Apr 21, 2023 at 10:42:57AM -0700, Casey Schaufler wrote:
> Add hooks for setselfattr and getselfattr. These hooks are not very
> different from their setprocattr and getprocattr equivalents, and
> much of the code is shared.
>
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
> Cc: John Johansen <john.johansen@canonical.com>
> ---
> security/apparmor/include/procattr.h | 2 +-
> security/apparmor/lsm.c | 96 ++++++++++++++++++++++++++--
> security/apparmor/procattr.c | 11 +++-
> 3 files changed, 99 insertions(+), 10 deletions(-)
>
> diff --git a/security/apparmor/include/procattr.h b/security/apparmor/include/procattr.h
> index 31689437e0e1..03dbfdb2f2c0 100644
> --- a/security/apparmor/include/procattr.h
> +++ b/security/apparmor/include/procattr.h
> @@ -11,7 +11,7 @@
> #ifndef __AA_PROCATTR_H
> #define __AA_PROCATTR_H
>
> -int aa_getprocattr(struct aa_label *label, char **string);
> +int aa_getprocattr(struct aa_label *label, char **string, bool newline);
> int aa_setprocattr_changehat(char *args, size_t size, int flags);
>
> #endif /* __AA_PROCATTR_H */
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index ce6ccb7e06ec..bdaa8bac0404 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -630,6 +630,45 @@ static int apparmor_sb_pivotroot(const struct path *old_path,
> return error;
> }
>
> +static int apparmor_getselfattr(unsigned int __user attr,
> + struct lsm_ctx __user *lx, size_t *size,
> + u32 __user flags)
> +{
> + int error = -ENOENT;
> + struct aa_task_ctx *ctx = task_ctx(current);
> + struct aa_label *label = NULL;
> + size_t total_len;
> + char *value;
> +
> + if (attr == LSM_ATTR_CURRENT)
> + label = aa_get_newest_label(cred_label(current_cred()));
> + else if (attr == LSM_ATTR_PREV && ctx->previous)
> + label = aa_get_newest_label(ctx->previous);
> + else if (attr == LSM_ATTR_EXEC && ctx->onexec)
> + label = aa_get_newest_label(ctx->onexec);
> + else
> + error = -EOPNOTSUPP;

Is "-EOPNOTSUPP" correct for LSM_ATTR_PREV when !ctx->previous? That
seems like it should be -EINVAL? I think this would be better served as
a switch statement.

> +
> + if (label) {
> + error = aa_getprocattr(label, &value, false);
> + if (error > 0) {
> + total_len = ALIGN(error + sizeof(*ctx), 8);
> + if (total_len > *size)
> + error = -E2BIG;
> + else
> + lsm_fill_user_ctx(lx, value, error,
> + LSM_ID_APPARMOR, 0);
> + }
> + }
> +
> + aa_put_label(label);
> +
> + *size = total_len;
> + if (error > 0)
> + return 1;
> + return error;
> +}
> +
> static int apparmor_getprocattr(struct task_struct *task, const char *name,
> char **value)
> {
> @@ -649,7 +688,7 @@ static int apparmor_getprocattr(struct task_struct *task, const char *name,
> error = -EINVAL;
>
> if (label)
> - error = aa_getprocattr(label, value);
> + error = aa_getprocattr(label, value, true);
>
> aa_put_label(label);
> put_cred(cred);
> @@ -657,8 +696,7 @@ static int apparmor_getprocattr(struct task_struct *task, const char *name,
> return error;
> }
>
> -static int apparmor_setprocattr(const char *name, void *value,
> - size_t size)
> +static int do_setattr(u64 attr, void *value, size_t size)
> {
> char *command, *largs = NULL, *args = value;
> size_t arg_size;
> @@ -689,7 +727,7 @@ static int apparmor_setprocattr(const char *name, void *value,
> goto out;
>
> arg_size = size - (args - (largs ? largs : (char *) value));
> - if (strcmp(name, "current") == 0) {
> + if (attr == LSM_ATTR_CURRENT) {
> if (strcmp(command, "changehat") == 0) {
> error = aa_setprocattr_changehat(args, arg_size,
> AA_CHANGE_NOFLAGS);
> @@ -704,7 +742,7 @@ static int apparmor_setprocattr(const char *name, void *value,
> error = aa_change_profile(args, AA_CHANGE_STACK);
> } else
> goto fail;
> - } else if (strcmp(name, "exec") == 0) {
> + } else if (attr == LSM_ATTR_EXEC) {
> if (strcmp(command, "exec") == 0)
> error = aa_change_profile(args, AA_CHANGE_ONEXEC);
> else if (strcmp(command, "stack") == 0)
> @@ -724,13 +762,57 @@ static int apparmor_setprocattr(const char *name, void *value,
>
> fail:
> aad(&sa)->label = begin_current_label_crit_section();
> - aad(&sa)->info = name;
> + if (attr == LSM_ATTR_CURRENT)
> + aad(&sa)->info = "current";
> + else if (attr == LSM_ATTR_EXEC)
> + aad(&sa)->info = "exec";
> + else
> + aad(&sa)->info = "invalid";
> aad(&sa)->error = error = -EINVAL;
> aa_audit_msg(AUDIT_APPARMOR_DENIED, &sa, NULL);
> end_current_label_crit_section(aad(&sa)->label);
> goto out;
> }
>
> +static int apparmor_setselfattr(unsigned int __user attr,
> + struct lsm_ctx __user *ctx, size_t __user size,
> + u32 __user flags)
> +{
> + struct lsm_ctx *lctx;
> + void *context;
> + int rc;
> +
> + if (attr != LSM_ATTR_CURRENT && attr != LSM_ATTR_EXEC)
> + return -EOPNOTSUPP;
> +
> + context = kmalloc(size, GFP_KERNEL);
> + if (context == NULL)
> + return -ENOMEM;
> +
> + lctx = (struct lsm_ctx *)context;
> + if (copy_from_user(context, ctx, size))
> + rc = -EFAULT;
> + else if (lctx->ctx_len > size)
> + rc = -EINVAL;
> + else
> + rc = do_setattr(attr, lctx + 1, lctx->ctx_len);
> +
> + kfree(context);
> + if (rc > 0)
> + return 0;
> + return rc;
> +}
> +
> +static int apparmor_setprocattr(const char *name, void *value,
> + size_t size)
> +{
> + int attr = lsm_name_to_attr(name);
> +
> + if (attr)
> + return do_setattr(attr, value, size);
> + return -EINVAL;
> +}
> +
> /**
> * apparmor_bprm_committing_creds - do task cleanup on committing new creds
> * @bprm: binprm for the exec (NOT NULL)
> @@ -1253,6 +1335,8 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
> LSM_HOOK_INIT(file_lock, apparmor_file_lock),
> LSM_HOOK_INIT(file_truncate, apparmor_file_truncate),
>
> + LSM_HOOK_INIT(getselfattr, apparmor_getselfattr),
> + LSM_HOOK_INIT(setselfattr, apparmor_setselfattr),
> LSM_HOOK_INIT(getprocattr, apparmor_getprocattr),
> LSM_HOOK_INIT(setprocattr, apparmor_setprocattr),
>
> diff --git a/security/apparmor/procattr.c b/security/apparmor/procattr.c
> index 197d41f9c32b..196f319aa3b2 100644
> --- a/security/apparmor/procattr.c
> +++ b/security/apparmor/procattr.c
> @@ -20,6 +20,7 @@
> * aa_getprocattr - Return the label information for @label
> * @label: the label to print label info about (NOT NULL)
> * @string: Returns - string containing the label info (NOT NULL)
> + * @newline: indicates that a newline should be added
> *
> * Requires: label != NULL && string != NULL
> *
> @@ -27,7 +28,7 @@
> *
> * Returns: size of string placed in @string else error code on failure
> */
> -int aa_getprocattr(struct aa_label *label, char **string)
> +int aa_getprocattr(struct aa_label *label, char **string, bool newline)
> {
> struct aa_ns *ns = labels_ns(label);
> struct aa_ns *current_ns = aa_get_current_ns();
> @@ -57,10 +58,14 @@ int aa_getprocattr(struct aa_label *label, char **string)
> return len;
> }
>
> - (*string)[len] = '\n';
> - (*string)[len + 1] = 0;
> + if (newline)
> + (*string)[len++] = '\n';
> + (*string)[len] = 0;
>
> aa_put_ns(current_ns);
> +
> + if (newline)
> + return len;
> return len + 1;
> }

This is returning the count including trailing %NUL, yes? Why is this
not always just "return len"? i.e.:

if (newline)
(*string)[len++] = '\n';
(*string)[len++] = 0;

aa_put_ns(current_ns);
return len;

>
> --
> 2.39.2
>

--
Kees Cook