There are several scenarios that have come up where having a user_event
persist even if the process that registered it exits. The main one is
having a daemon create events on bootup that shouldn't get deleted if
the daemon has to exit or reload. Another is within OpenTelemetry
exporters, they wish to potentially check if a user_event exists on the
system to determine if exporting the data out should occur. The
user_event in this case must exist even in the absence of the owning
process running (such as the above daemon case).
Expose the previously internal flag USER_EVENT_REG_PERSIST to user
processes. Upon register or delete of events with this flag, ensure the
user is perfmon_capable to prevent random user processes with access to
tracefs from creating events that persist after exit.
Signed-off-by: Beau Belgrave <be...@linux.microsoft.com>
---
include/uapi/linux/user_events.h | 11 +++++++++-
kernel/trace/trace_events_user.c | 36 +++++++++++++++++++-------------
2 files changed, 32 insertions(+), 15 deletions(-)
diff --git a/include/uapi/linux/user_events.h b/include/uapi/linux/user_events.h
index 2984aae4a2b4..f74f3aedd49c 100644
--- a/include/uapi/linux/user_events.h
+++ b/include/uapi/linux/user_events.h
@@ -17,6 +17,15 @@
/* Create dynamic location entry within a 32-bit value */
#define DYN_LOC(offset, size) ((size) << 16 | (offset))
+/* List of supported registration flags */
+enum user_reg_flag {
+ /* Event will not delete upon last reference closing */
+ USER_EVENT_REG_PERSIST = 1U << 0,
+
+ /* This value or above is currently non-ABI */
+ USER_EVENT_REG_MAX = 1U << 1,
+};
+
/*
* Describes an event registration and stores the results of the registration.
* This structure is passed to the DIAG_IOCSREG ioctl, callers at a minimum
@@ -33,7 +42,7 @@ struct user_reg {
/* Input: Enable size in bytes at address */
__u8 enable_size;
- /* Input: Flags for future use, set to 0 */
+ /* Input: Flags to use, if any */
__u16 flags;
/* Input: Address to update when enabled */
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 6f046650e527..e3f2b8d72e01 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -49,18 +49,6 @@
#define EVENT_STATUS_PERF BIT(1)
#define EVENT_STATUS_OTHER BIT(7)
-/*
- * User register flags are not allowed yet, keep them here until we are
- * ready to expose them out to the user ABI.
- */
-enum user_reg_flag {
- /* Event will not delete upon last reference closing */
- USER_EVENT_REG_PERSIST = 1U << 0,
-
- /* This value or above is currently non-ABI */
- USER_EVENT_REG_MAX = 1U << 1,
-};
-
/*
* Stores the system name, tables, and locks for a group of events. This
* allows isolation for events by various means.
@@ -191,6 +179,17 @@ static u32 user_event_key(char *name)
return jhash(name, strlen(name), 0);
}
+static bool user_event_capable(u16 reg_flags)
+{
+ /* Persistent events require CAP_PERFMON / CAP_SYS_ADMIN */
+ if (reg_flags & USER_EVENT_REG_PERSIST) {
+ if (!perfmon_capable())
+ return false;
+ }
+
+ return true;
+}
+
static struct user_event *user_event_get(struct user_event *user)
{
refcount_inc(&user->refcnt);
@@ -1773,6 +1772,9 @@ static int user_event_free(struct dyn_event *ev)
if (!user_event_last_ref(user))
return -EBUSY;
+ if (!user_event_capable(user->reg_flags))
+ return -EPERM;
+
return destroy_user_event(user);
}
@@ -1888,10 +1890,13 @@ static int user_event_parse(struct user_event_group
*group, char *name,
int argc = 0;
char **argv;
- /* User register flags are not ready yet */
- if (reg_flags != 0 || flags != NULL)
+ /* Currently don't support any text based flags */
+ if (flags != NULL)
return -EINVAL;
+ if (!user_event_capable(reg_flags))
+ return -EPERM;
+
/* Prevent dyn_event from racing */
mutex_lock(&event_mutex);
user = find_user_event(group, name, &key);
@@ -2024,6 +2029,9 @@ static int delete_user_event(struct user_event_group
*group, char *name)
if (!user_event_last_ref(user))
return -EBUSY;
+ if (!user_event_capable(user->reg_flags))
+ return -EPERM;
+
return destroy_user_event(user);
}
--
2.34.1
