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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: ba470eebc2 ("tracing/user_events: Prevent same name but different args event")
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 2024-04-23 16:23:37 +00:00 committed by Steven Rostedt (Google)
parent dd5a440a31
commit bd125a0840
1 changed files with 75 additions and 1 deletions
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76
kernel/trace/trace_events_user.c
View File

@ -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;