Re: [PATCH v2 2/3] fanotify: define struct members to hold response decision context

This patch adds 2 structure members to the response returned from user space on a permission event. The first field is 16 bits for the context type. The context type will describe what the meaning is of the second field. The default is none. The patch defines one additional context type which means that the second field is a 32-bit rule number. This will allow for the creation of other context types in the future if other users of the API identify different needs. The second field size is defined by the context type and can be used to pass along the data described by the context. To support this, there is a macro for user space to check that the data being sent is valid. Of course, without this check, anything that overflows the bit field will trigger an EINVAL based on the use of FAN_INVALID_RESPONSE_MASK in process_access_response(). Suggested-by: Steve Grubb <sgrubb(a)redhat.com&gt; Link: https://lore.kernel.org/r/2745105.e9J7NaK4W3@x2 Suggested-by: Jan Kara <jack(a)suse.cz&gt; Link: https://lore.kernel.org/r/20201001101219.GE17860@quack2.suse.cz Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; Link: https://lore.kernel.org/r/17660b3f2817e5c0a19d1e9e5d40b53ff4561845.165117... --- fs/notify/fanotify/fanotify.c | 1 - fs/notify/fanotify/fanotify.h | 4 +- fs/notify/fanotify/fanotify_user.c | 59 ++++++++++++++++++++---------- include/linux/fanotify.h | 3 ++ include/uapi/linux/fanotify.h | 27 +++++++++++++- 5 files changed, 72 insertions(+), 22 deletions(-) diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c index 985e995d2a39..00aff6e29bf8 100644 --- a/fs/notify/fanotify/fanotify.c +++ b/fs/notify/fanotify/fanotify.c @@ -266,7 +266,6 @@ static int fanotify_get_response(struct fsnotify_group *group, case FAN_ALLOW: ret = 0; break; - case FAN_DENY:

default: ret = -EPERM; }

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index 694516470660..f1ff4cf683fb 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -289,13 +289,19 @@ static int create_fd(struct fsnotify_group *group, struct path *path, */ static void finish_permission_event(struct fsnotify_group *group, struct fanotify_perm_event *event, - __u32 response) + struct fanotify_response *response) __releases(&group->notification_lock) { bool destroy = false; assert_spin_locked(&group->notification_lock); - event->response = response; + event->response = response->response; + event->extra_info_type = response->extra_info_type; + switch (event->extra_info_type) { + case FAN_RESPONSE_INFO_AUDIT_RULE: + memcpy(event->extra_info_buf, response->extra_info_buf, + sizeof(struct fanotify_response_audit_rule));

+ } if (event->state == FAN_EVENT_CANCELED) destroy = true; else

@@ -827,26 +845,25 @@ static ssize_t fanotify_read(struct file *file, char __user *buf, static ssize_t fanotify_write(struct file *file, const char __user *buf, size_t count, loff_t *pos) { - struct fanotify_response response = { .fd = -1, .response = -1 }; + struct fanotify_response response; struct fsnotify_group *group; int ret; + size_t size = min(count, sizeof(struct fanotify_response)); if (!IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS)) return -EINVAL; group = file->private_data; - if (count < sizeof(response)) + if (count < offsetof(struct fanotify_response, extra_info_buf)) return -EINVAL;

- count = sizeof(response); - pr_debug("%s: group=%p count=%zu\n", __func__, group, count); - if (copy_from_user(&response, buf, count)) + if (copy_from_user(&response, buf, size)) return -EFAULT; - ret = process_access_response(group, &response); + ret = process_access_response(group, &response, count); if (ret < 0) count = ret;

diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h index e8ac38cc2fd6..efb5a3a6f814 100644 --- a/include/uapi/linux/fanotify.h +++ b/include/uapi/linux/fanotify.h @@ -179,9 +179,34 @@ struct fanotify_event_info_error { __u32 error_count; }; +/* + * User space may need to record additional information about its decision. + * The extra information type records what kind of information is included. + * The default is none. We also define an extra informaion buffer whose + * size is determined by the extra information type. + * + * If the context type is Rule, then the context following is the rule number + * that triggered the user space decision. + */ + +#define FAN_RESPONSE_INFO_AUDIT_NONE 0 +#define FAN_RESPONSE_INFO_AUDIT_RULE 1 + +struct fanotify_response_audit_rule { + __u32 rule; +}; + +#define FANOTIFY_RESPONSE_EXTRA_LEN_MAX \ + (sizeof(union { \ + struct fanotify_response_audit_rule r; \ + /* add other extra info structures here */ \ + })) + struct fanotify_response { __s32 fd; - __u32 response; + __u16 response; + __u16 extra_info_type; + char extra_info_buf[FANOTIFY_RESPONSE_EXTRA_LEN_MAX]; };