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SubjectLSM hook for mount, superblock and keys watch notifications
Date
How about if I apply the attached patch?  It creates a new LSM hook that gets
called each time a notification is about to be posted on a queue. It is given
the creds from the /dev/watch_queue opener, the creds of whoever triggered the
watchpoint and a pointer to the notification message.

The notification message includes metadata describing the source/type of the
message and the subtype within that, plus subtype-specific flags.

David
---
diff --git a/drivers/misc/watch_queue.c b/drivers/misc/watch_queue.c
index 13c9f88e6953..3e7bb032ec17 100644
--- a/drivers/misc/watch_queue.c
+++ b/drivers/misc/watch_queue.c
@@ -23,6 +23,8 @@
#include <linux/uaccess.h>
#include <linux/vmalloc.h>
#include <linux/file.h>
+#include <linux/security.h>
+#include <linux/cred.h>
#include <linux/watch_queue.h>

#define DEBUG_WITH_WRITE /* Allow use of write() to record notifications */
@@ -50,6 +52,7 @@ struct watch_filter {
struct watch_queue {
struct rcu_head rcu;
struct address_space mapping;
+ const struct cred *cred; /* Creds of the owner of the queue */
struct watch_filter *filter;
wait_queue_head_t waiters;
struct hlist_head watches; /* Contributory watches */
@@ -82,7 +85,8 @@ struct watch_queue {
* should be in units of sizeof(*n).
*/
static bool post_one_notification(struct watch_queue *wqueue,
- struct watch_notification *n)
+ struct watch_notification *n,
+ const struct cred *cred)
{
struct watch_queue_buffer *buf = wqueue->buffer;
unsigned int metalen = sizeof(buf->meta) / sizeof(buf->slots[0]);
@@ -99,7 +103,8 @@ static bool post_one_notification(struct watch_queue *wqueue,

spin_lock(&wqueue->lock); /* Protect head pointer */

- if (wqueue->defunct)
+ if (wqueue->defunct ||
+ security_post_notification(wqueue->cred, cred, n) < 0)
goto out;

ring_tail = READ_ONCE(buf->meta.tail);
@@ -205,6 +210,7 @@ static bool filter_watch_notification(const struct watch_filter *wf,
* __post_watch_notification - Post an event notification
* @wlist: The watch list to post the event to.
* @n: The notification record to post.
+ * @cred: The creds of the process that triggered the notification.
* @id: The ID to match on the watch.
*
* Post a notification of an event into a set of watch queues and let the users
@@ -217,6 +223,7 @@ static bool filter_watch_notification(const struct watch_filter *wf,
*/
void __post_watch_notification(struct watch_list *wlist,
struct watch_notification *n,
+ const struct cred *cred,
u64 id)
{
const struct watch_filter *wf;
@@ -236,7 +243,7 @@ void __post_watch_notification(struct watch_list *wlist,
if (wf && !filter_watch_notification(wf, n))
continue;

- post_one_notification(wqueue, n);
+ post_one_notification(wqueue, n, cred);
}

rcu_read_unlock();
@@ -517,6 +524,7 @@ static int watch_queue_open(struct inode *inode, struct file *file)
refcount_set(&wqueue->usage, 1);
spin_lock_init(&wqueue->lock);
init_waitqueue_head(&wqueue->waiters);
+ wqueue->cred = get_cred(file->f_cred);

file->private_data = wqueue;
return 0;
@@ -615,7 +623,7 @@ int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
n.subtype = watch_meta_removal_notification;
n.info = watch->info_id | sizeof(n);

- post_one_notification(watch->queue, &n);
+ post_one_notification(watch->queue, &n, wq->cred);

/* We don't need the watch list lock for the next bit as RCU is
* protecting everything from being deallocated.
@@ -733,6 +741,7 @@ static int watch_queue_release(struct inode *inode, struct file *file)
if (wqueue->filter)
kfree_rcu(wqueue->filter, rcu);
kfree(wqueue->pages);
+ put_cred(wqueue->cred);
put_watch_queue(wqueue);
return 0;
}
@@ -760,7 +769,7 @@ static ssize_t watch_queue_write(struct file *file,
goto error;
n->info &= (WATCH_INFO_LENGTH | WATCH_INFO_TYPE_FLAGS | WATCH_INFO_ID);

- if (post_one_notification(wqueue, n))
+ if (post_one_notification(wqueue, n, current_cred()))
wqueue->debug = 0;
else
wqueue->debug++;
diff --git a/fs/mount_notify.c b/fs/mount_notify.c
index b4905c363136..6de6e701bf20 100644
--- a/fs/mount_notify.c
+++ b/fs/mount_notify.c
@@ -22,6 +22,7 @@
void post_mount_notification(struct mount *changed,
struct mount_notification *notify)
{
+ const struct cred *cred = current_cred();
struct path cursor;
struct mount *mnt;
unsigned seq;
@@ -40,7 +41,7 @@ void post_mount_notification(struct mount *changed,
!hlist_empty(&mnt->mnt_watchers->watchers)) {
if (cursor.dentry->d_flags & DCACHE_MOUNT_WATCH)
post_watch_notification(mnt->mnt_watchers,
- &notify->watch,
+ &notify->watch, cred,
(unsigned long)cursor.dentry);
} else {
cursor.dentry = mnt->mnt.mnt_root;
diff --git a/fs/super.c b/fs/super.c
index 1a1cf517dbd8..939ed08b87e9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1825,7 +1825,8 @@ EXPORT_SYMBOL(vfs_get_tree);
*/
void post_sb_notification(struct super_block *s, struct superblock_notification *n)
{
- post_watch_notification(s->s_watchers, &n->watch, s->s_watch_id);
+ post_watch_notification(s->s_watchers, &n->watch, current_cred(),
+ s->s_watch_id);
}

static void release_sb_watch(struct watch_list *wlist, struct watch *watch)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index b1a62dc0b8d9..08a61a5fecd4 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1439,6 +1439,13 @@
* @ctx is a pointer in which to place the allocated security context.
* @ctxlen points to the place to put the length of @ctx.
*
+ * @post_notification:
+ * Check to see if a watch notification can be posted to a particular
+ * queue.
+ * @q_cred: The credentials of the target watch queue.
+ * @cred: The event-triggerer's credentials
+ * @n: The notification being posted
+ *
* Security hooks for using the eBPF maps and programs functionalities through
* eBPF syscalls.
*
@@ -1713,6 +1720,11 @@ union security_list_options {
int (*inode_notifysecctx)(struct inode *inode, void *ctx, u32 ctxlen);
int (*inode_setsecctx)(struct dentry *dentry, void *ctx, u32 ctxlen);
int (*inode_getsecctx)(struct inode *inode, void **ctx, u32 *ctxlen);
+#ifdef CONFIG_WATCH_QUEUE
+ int (*post_notification)(const struct cred *q_cred,
+ const struct cred *cred,
+ struct watch_notification *n);
+#endif

#ifdef CONFIG_SECURITY_NETWORK
int (*unix_stream_connect)(struct sock *sock, struct sock *other,
@@ -1992,6 +2004,9 @@ struct security_hook_heads {
struct hlist_head inode_notifysecctx;
struct hlist_head inode_setsecctx;
struct hlist_head inode_getsecctx;
+#ifdef CONFIG_WATCH_QUEUE
+ struct hlist_head post_notification;
+#endif
#ifdef CONFIG_SECURITY_NETWORK
struct hlist_head unix_stream_connect;
struct hlist_head unix_may_send;
diff --git a/include/linux/security.h b/include/linux/security.h
index c73d9ba863bc..946ab7455a3f 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -392,6 +392,11 @@ void security_inode_invalidate_secctx(struct inode *inode);
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);
+#ifdef CONFIG_WATCH_QUEUE
+int security_post_notification(const struct cred *q_cred,
+ const struct cred *cred,
+ struct watch_notification *n);
+#endif
#else /* CONFIG_SECURITY */
struct security_mnt_opts {
};
@@ -1216,6 +1221,14 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
{
return -EOPNOTSUPP;
}
+#ifdef CONFIG_WATCH_QUEUE
+static inline int security_post_notification(const struct cred *q_cred,
+ const struct cred *cred,
+ struct watch_notification *n)
+{
+ return 0;
+}
+#endif
#endif /* CONFIG_SECURITY */

#ifdef CONFIG_SECURITY_NETWORK
diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index 465b14f3ad42..a1d20c917998 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -46,7 +46,9 @@ struct watch_list {
};

extern void __post_watch_notification(struct watch_list *,
- struct watch_notification *, u64);
+ struct watch_notification *,
+ const struct cred *,
+ u64);
extern struct watch_queue *get_watch_queue(int);
extern void put_watch_queue(struct watch_queue *);
extern void put_watch_list(struct watch_list *);
@@ -68,10 +70,11 @@ static inline void init_watch(struct watch *watch)

static inline void post_watch_notification(struct watch_list *wlist,
struct watch_notification *n,
+ const struct cred *cred,
u64 id)
{
if (unlikely(wlist))
- __post_watch_notification(wlist, n, id);
+ __post_watch_notification(wlist, n, cred, id);
}

static inline void remove_watch_list(struct watch_list *wlist)
diff --git a/security/keys/internal.h b/security/keys/internal.h
index 66b424e8c104..8394e42fe5ae 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -194,7 +194,8 @@ static inline void notify_key(struct key *key,
.aux = aux,
};

- post_watch_notification(key->watchers, &n.watch, n.key_id);
+ post_watch_notification(key->watchers, &n.watch, current_cred(),
+ n.key_id);
#endif
}

diff --git a/security/security.c b/security/security.c
index 2439a5613813..2e9c74ca3eac 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1375,6 +1375,15 @@ int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
}
EXPORT_SYMBOL(security_inode_getsecctx);

+#ifdef CONFIG_WATCH_QUEUE
+int security_post_notification(const struct cred *q_cred,
+ const struct cred *cred,
+ struct watch_notification *n)
+{
+ return call_int_hook(post_notification, 0, q_cred, cred, n);
+}
+#endif
+
#ifdef CONFIG_SECURITY_NETWORK

int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)
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