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

Fixes ba470eebc2f6 ("tracing/user_events: Prevent same name but different args event")

Signed-off-by Beau Belgrave <[email protected]>

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

kernel/trace/trace_events_user.c +2 -0

index 70d428c394b6..82b191f33a28 100644
@@ -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.

kernel/trace/trace_events_user.c +34 -0

+	}
+
+	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;
+}
+

Quoted 17 lines · On Tue, 23 Apr 2024 16:23:37 +0000 Beau Belgrave <[email protected]>…

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.

Quoted 5 lines

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

I'm curious, what happens if you have: "u8 field1; u8 field2;" ?

Do you care? As you will then create "u8 field1; u8 field2; "

but I'm guessing the extra whitespace at the end doesn't affect anything.

Quoted 18 lines

Fixes ba470eebc2f6 ("tracing/user_events: Prevent same name but different args event")

Signed-off-by Beau Belgrave <[email protected]>

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

kernel/trace/trace_events_user.c +2 -0

index 70d428c394b6..82b191f33a28 100644
@@ -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.

kernel/trace/trace_events_user.c static int user_event_set_tp_name(struct user_event *user) · line 2003

Quoted 10 lines

kernel/trace/trace_events_user.c +10 -0

+ */
+static int count_semis_no_space(char *args)
+{
+	int count = 0;
+
+	while ((args = strchr(args, ';'))) {
+		args++;
+
+		if (!isspace(*args))
+			count++;

This will count that "..;"

This is most likely not an issue, but since I didn't see this case anywhere, I figured I bring it up just to confirm that it's not an issue.

-- Steve

Quoted 34 lines

kernel/trace/trace_events_user.c +34 -0

+	}
+
+	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;
+}
+

It's not an issue on the matching/logic. However, you do get an extra byte alloc (which doesn't bother me in this edge case).

The ABI documentation indicates that field separators do not need a space between them, only a ';'. When no spacing is used, the register must work. Any subsequent register, with or without spaces, must match and not return -EADDRINUSE.

Add a non-spacing separator case to our self-test register case to ensure it works going forward.

Signed-off-by Beau Belgrave <[email protected]>

---
 tools/testing/selftests/user_events/ftrace_test.c | 8 ++++++++
 1 file changed, 8 insertions(+)

tools/testing/selftests/user_events/ftrace_test.c +8 -0

index dcd7509fe2e0..0bb46793dcd4 100644
@@ -261,6 +261,12 @@ TEST_F(user, register_events) {
 	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
 	ASSERT_EQ(0, reg.write_index);
 
+	/* Register without separator spacing should still match */
+	reg.enable_bit = 29;
+	reg.name_args = (__u64)"__test_event u32 field1;u32 field2";
+	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
+	ASSERT_EQ(0, reg.write_index);
+
 	/* Multiple registers to same name but different args should fail */
 	reg.enable_bit = 29;
 	reg.name_args = (__u64)"__test_event u32 field1;";

@@ -288,6 +294,8 @@ TEST_F(user, register_events) {
 	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSUNREG, &unreg));
 	unreg.disable_bit = 30;
 	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSUNREG, &unreg));
+	unreg.disable_bit = 29;
+	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSUNREG, &unreg));
 
 	/* Delete should have been auto-done after close and unregister */
 	close(self->data_fd);

Signature · 1 line

2.34.1