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user_events: Prevent dyn_event delete racing with ioctl add/delete 

Find user_events always while under the event_mutex and before leaving
the lock, add a ref count to the user_event. This ensures that all paths
under the event_mutex that check the ref counts will be synchronized.

The ioctl add/delete paths are protected by the reg_mutex. However,
dyn_event is only protected by the event_mutex. The dyn_event delete
path cannot acquire reg_mutex, since that could cause a deadlock between
the ioctl delete case acquiring event_mutex after acquiring the reg_mutex.

Link: https://lkml.kernel.org/r/20220310001141.1660-1-beaub@linux.microsoft.com

Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Beau Belgrave 2022-03-09 16:11:41 -08:00 committed by Steven Rostedt (Google)
parent 3a73333fb3
commit 7e348b325b
1 changed files with 40 additions and 6 deletions
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46
kernel/trace/trace_events_user.c
View File

@ -135,6 +135,8 @@ static struct list_head *user_event_get_fields(struct trace_event_call *call)
* NOTE: Offsets are from the user data perspective, they are not from the
* trace_entry/buffer perspective. We automatically add the common properties
* sizes to the offset for the user.
*
* Upon success user_event has its ref count increased by 1.
*/
static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
{
@ -593,8 +595,10 @@ static struct user_event *find_user_event(char *name, u32 *outkey)
*outkey = key;
hash_for_each_possible(register_table, user, node, key)
if (!strcmp(EVENT_NAME(user), name))
if (!strcmp(EVENT_NAME(user), name)) {
atomic_inc(&user->refcnt);
return user;
}
return NULL;
}
@ -883,7 +887,12 @@ static int user_event_create(const char *raw_command)
return -ENOMEM;
mutex_lock(&reg_mutex);
ret = user_event_parse_cmd(name, &user);
if (!ret)
atomic_dec(&user->refcnt);
mutex_unlock(&reg_mutex);
if (ret)
@ -1050,6 +1059,7 @@ static int user_event_trace_register(struct user_event *user)
/*
* Parses the event name, arguments and flags then registers if successful.
* The name buffer lifetime is owned by this method for success cases only.
* Upon success the returned user_event has its ref count increased by 1.
*/
static int user_event_parse(char *name, char *args, char *flags,
struct user_event **newuser)
@ -1057,7 +1067,12 @@ static int user_event_parse(char *name, char *args, char *flags,
int ret;
int index;
u32 key;
struct user_event *user = find_user_event(name, &key);
struct user_event *user;
/* Prevent dyn_event from racing */
mutex_lock(&event_mutex);
user = find_user_event(name, &key);
mutex_unlock(&event_mutex);
if (user) {
*newuser = user;
@ -1121,6 +1136,10 @@ static int user_event_parse(char *name, char *args, char *flags,
goto put_user;
user->index = index;
/* Ensure we track ref */
atomic_inc(&user->refcnt);
dyn_event_init(&user->devent, &user_event_dops);
dyn_event_add(&user->devent, &user->call);
set_bit(user->index, page_bitmap);
@ -1147,12 +1166,21 @@ static int delete_user_event(char *name)
if (!user)
return -ENOENT;
if (atomic_read(&user->refcnt) != 0)
return -EBUSY;
/* Ensure we are the last ref */
if (atomic_read(&user->refcnt) != 1) {
ret = -EBUSY;
goto put_ref;
}
mutex_lock(&event_mutex);
ret = destroy_user_event(user);
mutex_unlock(&event_mutex);
if (ret)
goto put_ref;
return ret;
put_ref:
/* No longer have this ref */
atomic_dec(&user->refcnt);
return ret;
}
@ -1340,6 +1368,9 @@ static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
ret = user_events_ref_add(file, user);
/* No longer need parse ref, ref_add either worked or not */
atomic_dec(&user->refcnt);
/* Positive number is index and valid */
if (ret < 0)
return ret;
@ -1364,7 +1395,10 @@ static long user_events_ioctl_del(struct file *file, unsigned long uarg)
if (IS_ERR(name))
return PTR_ERR(name);
/* event_mutex prevents dyn_event from racing */
mutex_lock(&event_mutex);
ret = delete_user_event(name);
mutex_unlock(&event_mutex);
kfree(name);