Commit bd125a08 authored by Beau Belgrave's avatar Beau Belgrave Committed by Steven Rostedt (Google)
Browse files

tracing/user_events: Fix non-spaced field matching 

When the ABI was updated to prevent same name w/different args, it
missed an important corner case when fields don't end with a space.
Typically, space is used for fields to help separate them, like
"u8 field1; u8 field2". If no spaces are used, like
"u8 field1;u8 field2", then the parsing works for the first time.
However, the match check fails on a subsequent register, leading to
confusion.

This is because the match check uses argv_split() and assumes that all
fields will be split upon the space. When spaces are used, we get back
{ "u8", "field1;" }, without spaces we get back { "u8", "field1;u8" }.
This causes a mismatch, and the user program gets back -EADDRINUSE.

Add a method to detect this case before calling argv_split(). If found
force a space after the field separator character ';'. This ensures all
cases work properly for matching.

With this fix, the following are all treated as matching:
u8 field1;u8 field2
u8 field1; u8 field2
u8 field1;\tu8 field2
u8 field1;\nu8 field2

Link: https://lore.kernel.org/linux-trace-kernel/20240423162338.292-2-beaub@linux.microsoft.com



Fixes: ba470eeb ("tracing/user_events: Prevent same name but different args event")
Signed-off-by: default avatarBeau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent dd5a440a

kernel/trace/trace_events_user.c

+75 −1
Original line number Diff line number Diff line
@@ -1989,6 +1989,80 @@ static int user_event_set_tp_name(struct user_event *user) 
	return 0;

}



/*

 * Counts how many ';' without a trailing space are in the args.

 */

static int count_semis_no_space(char *args)

{

	int count = 0;



	while ((args = strchr(args, ';'))) {

		args++;



		if (!isspace(*args))

			count++;

	}



	return count;

}



/*

 * Copies the arguments while ensuring all ';' have a trailing space.

 */

static char *insert_space_after_semis(char *args, int count)

{

	char *fixed, *pos;

	int len;



	len = strlen(args) + count;

	fixed = kmalloc(len + 1, GFP_KERNEL);



	if (!fixed)

		return NULL;



	pos = fixed;



	/* Insert a space after ';' if there is no trailing space. */

	while (*args) {

		*pos = *args++;



		if (*pos++ == ';' && !isspace(*args))

			*pos++ = ' ';

	}



	*pos = '\0';



	return fixed;

}



static char **user_event_argv_split(char *args, int *argc)

{

	char **split;

	char *fixed;

	int count;



	/* Count how many ';' without a trailing space */

	count = count_semis_no_space(args);



	/* No fixup is required */

	if (!count)

		return argv_split(GFP_KERNEL, args, argc);



	/* We must fixup 'field;field' to 'field; field' */

	fixed = insert_space_after_semis(args, count);



	if (!fixed)

		return NULL;



	/* We do a normal split afterwards */

	split = argv_split(GFP_KERNEL, fixed, argc);



	/* We can free since argv_split makes a copy */

	kfree(fixed);



	return split;

}



/*

 * Parses the event name, arguments and flags then registers if successful.

 * The name buffer lifetime is owned by this method for success cases only.
@@ -2012,7 +2086,7 @@ static int user_event_parse(struct user_event_group *group, char *name, 
		return -EPERM;



	if (args) {

		argv = argv_split(GFP_KERNEL, args, &argc);

		argv = user_event_argv_split(args, &argc);



		if (!argv)

			return -ENOMEM;