[PATCH v2 0/2] tracing/user_events: Fix non-spaced field matching

[PATCH v2 0/2] tracing/user_events: Fix non-spaced field matching

[Beau Belgrave]

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.

I could not find an existing function to accomplish this, so I had to
hand code a copy with this logic. If there is a better way to achieve
this, I'm all ears.

This series also adds a selftest to ensure this doesn't break again.

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

V2 changes:
  Renamed fix_semis_no_space() to insert_space_after_semis().
  Have user_event_argv_split() return fast in no-split case.
  Pulled in Masami's shorter loop in insert_space_after_semis().

Beau Belgrave (2):
  tracing/user_events: Fix non-spaced field matching
  selftests/user_events: Add non-spacing separator check

 kernel/trace/trace_events_user.c              | 76 ++++++++++++++++++-
 .../selftests/user_events/ftrace_test.c       |  8 ++
 2 files changed, 83 insertions(+), 1 deletion(-)


base-commit: 0bbac3facb5d6cc0171c45c9873a2dc96bea9680
-- 
2.34.1

[PATCH v2 1/2] tracing/user_events: Fix non-spaced field matching

[Beau Belgrave]

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 <beaub@linux.microsoft.com>
---
 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;
-- 
2.34.1

[PATCH v2 2/2] selftests/user_events: Add non-spacing separator check

[Beau Belgrave]

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 <beaub@linux.microsoft.com>
---
 tools/testing/selftests/user_events/ftrace_test.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tools/testing/selftests/user_events/ftrace_test.c b/tools/testing/selftests/user_events/ftrace_test.c
index dcd7509fe2e0..0bb46793dcd4 100644
--- a/tools/testing/selftests/user_events/ftrace_test.c
+++ b/tools/testing/selftests/user_events/ftrace_test.c
@@ -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);
-- 
2.34.1

Re: [PATCH v2 1/2] tracing/user_events: Fix non-spaced field matching

[Steven Rostedt]

On Tue, 23 Apr 2024 16:23:37 +0000
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> 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

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.


> 
> Fixes: ba470eebc2f6 ("tracing/user_events: Prevent same name but different args event")
> Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
> ---
>  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++;

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


> +	}
> +
> +	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;
> +}
> +

Re: [PATCH v2 1/2] tracing/user_events: Fix non-spaced field matching

[Beau Belgrave]

On Thu, May 02, 2024 at 05:16:34PM -0400, Steven Rostedt wrote:
> On Tue, 23 Apr 2024 16:23:37 +0000
> Beau Belgrave <beaub@linux.microsoft.com> wrote:
> 
> > 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
> 
> I'm curious, what happens if you have: "u8 field1; u8 field2;" ?
> 

You'll get an extra whitespace during the copy, assuming it was really:
"u8 field1;u8 field2"

If it had spaces, this code wouldn't run.

> 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.
> 

Right, you get an extra byte allocated, but the argv_split() with ignore
it. The compare will work correctly (I've verified this just now to
double check).

IE these all match:
"Test u8 a; u8 b; "
"Test u8 a; u8 b;"
"Test u8 a; u8 b"

> 
> > 
> > Fixes: ba470eebc2f6 ("tracing/user_events: Prevent same name but different args event")
> > Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
> > ---
> >  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++;
> 
> 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.
> 

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).

Thanks,
-Beau

> -- Steve
> 
> 
> > +	}
> > +
> > +	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;
> > +}
> > +

Re: [PATCH v2 1/2] tracing/user_events: Fix non-spaced field matching

[Steven Rostedt]

On Thu, 2 May 2024 15:58:53 -0700
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> 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).

Figured as much, but since there was no mention of it, I decided to bring
it up.

I'll take this as-is then.

-- Steve