blob: 6b9c27548997162420250a1dfc810b4d293e3436 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
#include <linux/fanotify.h>
#include <linux/fdtable.h>
#include <linux/fsnotify_backend.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h> /* UINT_MAX */
#include <linux/mount.h>
#include <linux/sched.h>
#include <linux/sched/user.h>
#include <linux/sched/signal.h>
#include <linux/types.h>
#include <linux/wait.h>
#include <linux/audit.h>
#include <linux/sched/mm.h>
#include <linux/statfs.h>
#include "fanotify.h"
static bool should_merge(struct fsnotify_event *old_fsn,
struct fsnotify_event *new_fsn)
{
struct fanotify_event *old, *new;
pr_debug("%s: old=%p new=%p\n", __func__, old_fsn, new_fsn);
old = FANOTIFY_E(old_fsn);
new = FANOTIFY_E(new_fsn);
if (old_fsn->inode != new_fsn->inode || old->pid != new->pid ||
old->fh_type != new->fh_type || old->fh_len != new->fh_len)
return false;
if (fanotify_event_has_path(old)) {
return old->path.mnt == new->path.mnt &&
old->path.dentry == new->path.dentry;
} else if (fanotify_event_has_fid(old)) {
/*
* We want to merge many dirent events in the same dir (i.e.
* creates/unlinks/renames), but we do not want to merge dirent
* events referring to subdirs with dirent events referring to
* non subdirs, otherwise, user won't be able to tell from a
* mask FAN_CREATE|FAN_DELETE|FAN_ONDIR if it describes mkdir+
* unlink pair or rmdir+create pair of events.
*/
return (old->mask & FS_ISDIR) == (new->mask & FS_ISDIR) &&
fanotify_fid_equal(&old->fid, &new->fid, old->fh_len);
}
/* Do not merge events if we failed to encode fid */
return false;
}
/* and the list better be locked by something too! */
static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
{
struct fsnotify_event *test_event;
struct fanotify_event *new;
pr_debug("%s: list=%p event=%p\n", __func__, list, event);
new = FANOTIFY_E(event);
/*
* Don't merge a permission event with any other event so that we know
* the event structure we have created in fanotify_handle_event() is the
* one we should check for permission response.
*/
if (fanotify_is_perm_event(new->mask))
return 0;
list_for_each_entry_reverse(test_event, list, list) {
if (should_merge(test_event, event)) {
FANOTIFY_E(test_event)->mask |= new->mask;
return 1;
}
}
return 0;
}
/*
* Wait for response to permission event. The function also takes care of
* freeing the permission event (or offloads that in case the wait is canceled
* by a signal). The function returns 0 in case access got allowed by userspace,
* -EPERM in case userspace disallowed the access, and -ERESTARTSYS in case
* the wait got interrupted by a signal.
*/
static int fanotify_get_response(struct fsnotify_group *group,
struct fanotify_perm_event *event,
struct fsnotify_iter_info *iter_info)
{
int ret;
pr_debug("%s: group=%p event=%p\n", __func__, group, event);
ret = wait_event_killable(group->fanotify_data.access_waitq,
event->state == FAN_EVENT_ANSWERED);
/* Signal pending? */
if (ret < 0) {
spin_lock(&group->notification_lock);
/* Event reported to userspace and no answer yet? */
if (event->state == FAN_EVENT_REPORTED) {
/* Event will get freed once userspace answers to it */
event->state = FAN_EVENT_CANCELED;
spin_unlock(&group->notification_lock);
return ret;
}
/* Event not yet reported? Just remove it. */
if (event->state == FAN_EVENT_INIT)
fsnotify_remove_queued_event(group, &event->fae.fse);
/*
* Event may be also answered in case signal delivery raced
* with wakeup. In that case we have nothing to do besides
* freeing the event and reporting error.
*/
spin_unlock(&group->notification_lock);
goto out;
}
/* userspace responded, convert to something usable */
switch (event->response & ~FAN_AUDIT) {
case FAN_ALLOW:
ret = 0;
break;
case FAN_DENY:
default:
ret = -EPERM;
}
/* Check if the response should be audited */
if (event->response & FAN_AUDIT)
audit_fanotify(event->response & ~FAN_AUDIT);
pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
group, event, ret);
out:
fsnotify_destroy_event(group, &event->fae.fse);
return ret;
}
/*
* This function returns a mask for an event that only contains the flags
* that have been specifically requested by the user. Flags that may have
* been included within the event mask, but have not been explicitly
* requested by the user, will not be present in the returned mask.
*/
static u32 fanotify_group_event_mask(struct fsnotify_group *group,
struct fsnotify_iter_info *iter_info,
u32 event_mask, const void *data,
int data_type)
{
__u32 marks_mask = 0, marks_ignored_mask = 0;
__u32 test_mask, user_mask = FANOTIFY_OUTGOING_EVENTS;
const struct path *path = data;
struct fsnotify_mark *mark;
int type;
pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
__func__, iter_info->report_mask, event_mask, data, data_type);
if (!FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
/* Do we have path to open a file descriptor? */
if (data_type != FSNOTIFY_EVENT_PATH)
return 0;
/* Path type events are only relevant for files and dirs */
if (!d_is_reg(path->dentry) && !d_can_lookup(path->dentry))
return 0;
}
fsnotify_foreach_obj_type(type) {
if (!fsnotify_iter_should_report_type(iter_info, type))
continue;
mark = iter_info->marks[type];
/*
* If the event is for a child and this mark doesn't care about
* events on a child, don't send it!
*/
if (event_mask & FS_EVENT_ON_CHILD &&
(type != FSNOTIFY_OBJ_TYPE_INODE ||
!(mark->mask & FS_EVENT_ON_CHILD)))
continue;
marks_mask |= mark->mask;
marks_ignored_mask |= mark->ignored_mask;
}
test_mask = event_mask & marks_mask & ~marks_ignored_mask;
/*
* dirent modification events (create/delete/move) do not carry the
* child entry name/inode information. Instead, we report FAN_ONDIR
* for mkdir/rmdir so user can differentiate them from creat/unlink.
*
* For backward compatibility and consistency, do not report FAN_ONDIR
* to user in legacy fanotify mode (reporting fd) and report FAN_ONDIR
* to user in FAN_REPORT_FID mode for all event types.
*/
if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
/* Do not report FAN_ONDIR without any event */
if (!(test_mask & ~FAN_ONDIR))
return 0;
} else {
user_mask &= ~FAN_ONDIR;
}
if (event_mask & FS_ISDIR &&
!(marks_mask & FS_ISDIR & ~marks_ignored_mask))
return 0;
return test_mask & user_mask;
}
static int fanotify_encode_fid(struct fanotify_event *event,
struct inode *inode, gfp_t gfp,
__kernel_fsid_t *fsid)
{
struct fanotify_fid *fid = &event->fid;
int dwords, bytes = 0;
int err, type;
fid->ext_fh = NULL;
dwords = 0;
err = -ENOENT;
type = exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
if (!dwords)
goto out_err;
bytes = dwords << 2;
if (bytes > FANOTIFY_INLINE_FH_LEN) {
/* Treat failure to allocate fh as failure to allocate event */
err = -ENOMEM;
fid->ext_fh = kmalloc(bytes, gfp);
if (!fid->ext_fh)
goto out_err;
}
type = exportfs_encode_inode_fh(inode, fanotify_fid_fh(fid, bytes),
&dwords, NULL);
err = -EINVAL;
if (!type || type == FILEID_INVALID || bytes != dwords << 2)
goto out_err;
fid->fsid = *fsid;
event->fh_len = bytes;
return type;
out_err:
pr_warn_ratelimited("fanotify: failed to encode fid (fsid=%x.%x, "
"type=%d, bytes=%d, err=%i)\n",
fsid->val[0], fsid->val[1], type, bytes, err);
kfree(fid->ext_fh);
fid->ext_fh = NULL;
event->fh_len = 0;
return FILEID_INVALID;
}
/*
* The inode to use as identifier when reporting fid depends on the event.
* Report the modified directory inode on dirent modification events.
* Report the "victim" inode otherwise.
* For example:
* FS_ATTRIB reports the child inode even if reported on a watched parent.
* FS_CREATE reports the modified dir inode and not the created inode.
*/
static struct inode *fanotify_fid_inode(struct inode *to_tell, u32 event_mask,
const void *data, int data_type)
{
if (event_mask & ALL_FSNOTIFY_DIRENT_EVENTS)
return to_tell;
else if (data_type == FSNOTIFY_EVENT_INODE)
return (struct inode *)data;
else if (data_type == FSNOTIFY_EVENT_PATH)
return d_inode(((struct path *)data)->dentry);
return NULL;
}
struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
struct inode *inode, u32 mask,
const void *data, int data_type,
__kernel_fsid_t *fsid)
{
struct fanotify_event *event = NULL;
gfp_t gfp = GFP_KERNEL_ACCOUNT;
struct inode *id = fanotify_fid_inode(inode, mask, data, data_type);
/*
* For queues with unlimited length lost events are not expected and
* can possibly have security implications. Avoid losing events when
* memory is short.
*/
if (group->max_events == UINT_MAX)
gfp |= __GFP_NOFAIL;
/* Whoever is interested in the event, pays for the allocation. */
memalloc_use_memcg(group->memcg);
if (fanotify_is_perm_event(mask)) {
struct fanotify_perm_event *pevent;
pevent = kmem_cache_alloc(fanotify_perm_event_cachep, gfp);
if (!pevent)
goto out;
event = &pevent->fae;
pevent->response = 0;
pevent->state = FAN_EVENT_INIT;
goto init;
}
event = kmem_cache_alloc(fanotify_event_cachep, gfp);
if (!event)
goto out;
init: __maybe_unused
fsnotify_init_event(&event->fse, inode);
event->mask = mask;
if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
event->pid = get_pid(task_pid(current));
else
event->pid = get_pid(task_tgid(current));
event->fh_len = 0;
if (id && FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
/* Report the event without a file identifier on encode error */
event->fh_type = fanotify_encode_fid(event, id, gfp, fsid);
} else if (data_type == FSNOTIFY_EVENT_PATH) {
event->fh_type = FILEID_ROOT;
event->path = *((struct path *)data);
path_get(&event->path);
} else {
event->fh_type = FILEID_INVALID;
event->path.mnt = NULL;
event->path.dentry = NULL;
}
out:
memalloc_unuse_memcg();
return event;
}
/*
* Get cached fsid of the filesystem containing the object from any connector.
* All connectors are supposed to have the same fsid, but we do not verify that
* here.
*/
static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
{
int type;
__kernel_fsid_t fsid = {};
fsnotify_foreach_obj_type(type) {
if (!fsnotify_iter_should_report_type(iter_info, type))
continue;
fsid = iter_info->marks[type]->connector->fsid;
if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
continue;
return fsid;
}
return fsid;
}
static int fanotify_handle_event(struct fsnotify_group *group,
struct inode *inode,
u32 mask, const void *data, int data_type,
const unsigned char *file_name, u32 cookie,
struct fsnotify_iter_info *iter_info)
{
int ret = 0;
struct fanotify_event *event;
struct fsnotify_event *fsn_event;
__kernel_fsid_t fsid = {};
BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
BUILD_BUG_ON(FAN_ATTRIB != FS_ATTRIB);
BUILD_BUG_ON(FAN_CLOSE_NOWRITE != FS_CLOSE_NOWRITE);
BUILD_BUG_ON(FAN_CLOSE_WRITE != FS_CLOSE_WRITE);
BUILD_BUG_ON(FAN_OPEN != FS_OPEN);
BUILD_BUG_ON(FAN_MOVED_TO != FS_MOVED_TO);
BUILD_BUG_ON(FAN_MOVED_FROM != FS_MOVED_FROM);
BUILD_BUG_ON(FAN_CREATE != FS_CREATE);
BUILD_BUG_ON(FAN_DELETE != FS_DELETE);
BUILD_BUG_ON(FAN_DELETE_SELF != FS_DELETE_SELF);
BUILD_BUG_ON(FAN_MOVE_SELF != FS_MOVE_SELF);
BUILD_BUG_ON(FAN_EVENT_ON_CHILD != FS_EVENT_ON_CHILD);
BUILD_BUG_ON(FAN_Q_OVERFLOW != FS_Q_OVERFLOW);
BUILD_BUG_ON(FAN_OPEN_PERM != FS_OPEN_PERM);
BUILD_BUG_ON(FAN_ACCESS_PERM != FS_ACCESS_PERM);
BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
BUILD_BUG_ON(FAN_OPEN_EXEC != FS_OPEN_EXEC);
BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 19);
mask = fanotify_group_event_mask(group, iter_info, mask, data,
data_type);
if (!mask)
return 0;
pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
mask);
if (fanotify_is_perm_event(mask)) {
/*
* fsnotify_prepare_user_wait() fails if we race with mark
* deletion. Just let the operation pass in that case.
*/
if (!fsnotify_prepare_user_wait(iter_info))
return 0;
}
if (FAN_GROUP_FLAG(group, FAN_REPORT_FID))
fsid = fanotify_get_fsid(iter_info);
event = fanotify_alloc_event(group, inode, mask, data, data_type,
&fsid);
ret = -ENOMEM;
if (unlikely(!event)) {
/*
* We don't queue overflow events for permission events as
* there the access is denied and so no event is in fact lost.
*/
if (!fanotify_is_perm_event(mask))
fsnotify_queue_overflow(group);
goto finish;
}
fsn_event = &event->fse;
ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
if (ret) {
/* Permission events shouldn't be merged */
BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
/* Our event wasn't used in the end. Free it. */
fsnotify_destroy_event(group, fsn_event);
ret = 0;
} else if (fanotify_is_perm_event(mask)) {
ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
iter_info);
}
finish:
if (fanotify_is_perm_event(mask))
fsnotify_finish_user_wait(iter_info);
return ret;
}
static void fanotify_free_group_priv(struct fsnotify_group *group)
{
struct user_struct *user;
user = group->fanotify_data.user;
atomic_dec(&user->fanotify_listeners);
free_uid(user);
}
static void fanotify_free_event(struct fsnotify_event *fsn_event)
{
struct fanotify_event *event;
event = FANOTIFY_E(fsn_event);
if (fanotify_event_has_path(event))
path_put(&event->path);
else if (fanotify_event_has_ext_fh(event))
kfree(event->fid.ext_fh);
put_pid(event->pid);
if (fanotify_is_perm_event(event->mask)) {
kmem_cache_free(fanotify_perm_event_cachep,
FANOTIFY_PE(fsn_event));
return;
}
kmem_cache_free(fanotify_event_cachep, event);
}
static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
{
kmem_cache_free(fanotify_mark_cache, fsn_mark);
}
const struct fsnotify_ops fanotify_fsnotify_ops = {
.handle_event = fanotify_handle_event,
.free_group_priv = fanotify_free_group_priv,
.free_event = fanotify_free_event,
.free_mark = fanotify_free_mark,
};