[for-linus][PATCH 1/9] tracing/user_events: Fix non-spaced field matching

Steven Rostedt
2024-05-03T22:50:34Z

From: Beau Belgrave <beaub@linux.microsoft.com>

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: ba470eebc2f6 ("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>
---
kernel/trace/trace_events_user.c | 76 +++++++++++++++++++++++++++++++-
1 file changed, 75 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 70d428c394b6..82b191f33a28 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -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;
--
2.43.0