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

[PATCH 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

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              | 88 ++++++++++++++++++-
 .../selftests/user_events/ftrace_test.c       |  8 ++
 2 files changed, 95 insertions(+), 1 deletion(-)


base-commit: 0bbac3facb5d6cc0171c45c9873a2dc96bea9680
-- 
2.34.1

[PATCH 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 | 88 +++++++++++++++++++++++++++++++-
 1 file changed, 87 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 70d428c394b6..9184d3962b2a 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -1989,6 +1989,92 @@ 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 *fix_semis_no_space(char *args, int count)
+{
+	char *fixed, *pos;
+	char c, last;
+	int len;
+
+	len = strlen(args) + count;
+	fixed = kmalloc(len + 1, GFP_KERNEL);
+
+	if (!fixed)
+		return NULL;
+
+	pos = fixed;
+	last = '\0';
+
+	while (len > 0) {
+		c = *args++;
+
+		if (last == ';' && !isspace(c)) {
+			*pos++ = ' ';
+			len--;
+		}
+
+		if (len > 0) {
+			*pos++ = c;
+			len--;
+		}
+
+		last = c;
+	}
+
+	/*
+	 * len is the length of the copy excluding the null.
+	 * This ensures we always have room for a null.
+	 */
+	*pos = '\0';
+
+	return fixed;
+}
+
+static char **user_event_argv_split(char *args, int *argc)
+{
+	/* Count how many ';' without a trailing space */
+	int count = count_semis_no_space(args);
+
+	if (count) {
+		/* We must fixup 'field;field' to 'field; field' */
+		char *fixed = fix_semis_no_space(args, count);
+		char **split;
+
+		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;
+	}
+
+	/* No fixup is required */
+	return argv_split(GFP_KERNEL, args, argc);
+}
+
 /*
  * 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 +2098,7 @@ 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 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 1/2] tracing/user_events: Fix non-spaced field matching

[Masami Hiramatsu]

On Tue, 16 Apr 2024 22:41:01 +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

Sounds good to me. I just have some nits.

> 
> 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 | 88 +++++++++++++++++++++++++++++++-
>  1 file changed, 87 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> index 70d428c394b6..9184d3962b2a 100644
> --- a/kernel/trace/trace_events_user.c
> +++ b/kernel/trace/trace_events_user.c
> @@ -1989,6 +1989,92 @@ 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 *fix_semis_no_space(char *args, int count)

nit: This name does not represent what it does. 'insert_space_after_semis()'
is more self-described.

> +{
> +	char *fixed, *pos;
> +	char c, last;
> +	int len;
> +
> +	len = strlen(args) + count;
> +	fixed = kmalloc(len + 1, GFP_KERNEL);
> +
> +	if (!fixed)
> +		return NULL;
> +
> +	pos = fixed;
> +	last = '\0';
> +
> +	while (len > 0) {
> +		c = *args++;
> +
> +		if (last == ';' && !isspace(c)) {
> +			*pos++ = ' ';
> +			len--;
> +		}
> +
> +		if (len > 0) {
> +			*pos++ = c;
> +			len--;
> +		}
> +
> +		last = c;
> +	}

nit: This loop can be simpler, because we are sure fixed has enough length;

/* insert a space after ';' if there is no space. */
while(*args) {
	*pos = *args++;
	if (*pos++ == ';' && !isspace(*args))
		*pos++ = ' ';
}

> +
> +	/*
> +	 * len is the length of the copy excluding the null.
> +	 * This ensures we always have room for a null.
> +	 */
> +	*pos = '\0';
> +
> +	return fixed;
> +}
> +
> +static char **user_event_argv_split(char *args, int *argc)
> +{
> +	/* Count how many ';' without a trailing space */
> +	int count = count_semis_no_space(args);
> +
> +	if (count) {

nit: it is better to exit fast, so 

	if (!count)
		return argv_split(GFP_KERNEL, args, argc);

	...

Thank you,

OT: BTW, can this also simplify synthetic events?

> +		/* We must fixup 'field;field' to 'field; field' */
> +		char *fixed = fix_semis_no_space(args, count);
> +		char **split;
> +
> +		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;
> +	}
> +
> +	/* No fixup is required */
> +	return argv_split(GFP_KERNEL, args, argc);
> +}
> +
>  /*
>   * 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 +2098,7 @@ 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
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

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

[Beau Belgrave]

On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote:
> On Tue, 16 Apr 2024 22:41:01 +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
> 
> Sounds good to me. I just have some nits.
> 
> > 
> > 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 | 88 +++++++++++++++++++++++++++++++-
> >  1 file changed, 87 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> > index 70d428c394b6..9184d3962b2a 100644
> > --- a/kernel/trace/trace_events_user.c
> > +++ b/kernel/trace/trace_events_user.c
> > @@ -1989,6 +1989,92 @@ 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 *fix_semis_no_space(char *args, int count)
> 
> nit: This name does not represent what it does. 'insert_space_after_semis()'
> is more self-described.
> 

Sure, will fix in a v2.

> > +{
> > +	char *fixed, *pos;
> > +	char c, last;
> > +	int len;
> > +
> > +	len = strlen(args) + count;
> > +	fixed = kmalloc(len + 1, GFP_KERNEL);
> > +
> > +	if (!fixed)
> > +		return NULL;
> > +
> > +	pos = fixed;
> > +	last = '\0';
> > +
> > +	while (len > 0) {
> > +		c = *args++;
> > +
> > +		if (last == ';' && !isspace(c)) {
> > +			*pos++ = ' ';
> > +			len--;
> > +		}
> > +
> > +		if (len > 0) {
> > +			*pos++ = c;
> > +			len--;
> > +		}
> > +
> > +		last = c;
> > +	}
> 
> nit: This loop can be simpler, because we are sure fixed has enough length;
> 
> /* insert a space after ';' if there is no space. */
> while(*args) {
> 	*pos = *args++;
> 	if (*pos++ == ';' && !isspace(*args))
> 		*pos++ = ' ';
> }
> 

I was worried that if count_semis_no_space() ever had different logic
(maybe after this commit) that it could cause an overflow if the count
was wrong, etc.

I don't have an issue making it shorter, but I was trying to be more on
the safe side, since this isn't a fast path (event register).

> > +
> > +	/*
> > +	 * len is the length of the copy excluding the null.
> > +	 * This ensures we always have room for a null.
> > +	 */
> > +	*pos = '\0';
> > +
> > +	return fixed;
> > +}
> > +
> > +static char **user_event_argv_split(char *args, int *argc)
> > +{
> > +	/* Count how many ';' without a trailing space */
> > +	int count = count_semis_no_space(args);
> > +
> > +	if (count) {
> 
> nit: it is better to exit fast, so 
> 
> 	if (!count)
> 		return argv_split(GFP_KERNEL, args, argc);
> 
> 	...

Sure, will fix in a v2.

> 
> Thank you,
> 
> OT: BTW, can this also simplify synthetic events?
> 

I'm not sure, I'll check when I have some time. I want to get this fix
in sooner rather than later.

Thanks,
-Beau

> > +		/* We must fixup 'field;field' to 'field; field' */
> > +		char *fixed = fix_semis_no_space(args, count);
> > +		char **split;
> > +
> > +		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;
> > +	}
> > +
> > +	/* No fixup is required */
> > +	return argv_split(GFP_KERNEL, args, argc);
> > +}
> > +
> >  /*
> >   * 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 +2098,7 @@ 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
> > 
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

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

[Masami Hiramatsu]

On Fri, 19 Apr 2024 14:13:34 -0700
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote:
> > On Tue, 16 Apr 2024 22:41:01 +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
> > 
> > Sounds good to me. I just have some nits.
> > 
> > > 
> > > 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 | 88 +++++++++++++++++++++++++++++++-
> > >  1 file changed, 87 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
> > > index 70d428c394b6..9184d3962b2a 100644
> > > --- a/kernel/trace/trace_events_user.c
> > > +++ b/kernel/trace/trace_events_user.c
> > > @@ -1989,6 +1989,92 @@ 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 *fix_semis_no_space(char *args, int count)
> > 
> > nit: This name does not represent what it does. 'insert_space_after_semis()'
> > is more self-described.
> > 
> 
> Sure, will fix in a v2.
> 
> > > +{
> > > +	char *fixed, *pos;
> > > +	char c, last;
> > > +	int len;
> > > +
> > > +	len = strlen(args) + count;
> > > +	fixed = kmalloc(len + 1, GFP_KERNEL);
> > > +
> > > +	if (!fixed)
> > > +		return NULL;
> > > +
> > > +	pos = fixed;
> > > +	last = '\0';
> > > +
> > > +	while (len > 0) {
> > > +		c = *args++;
> > > +
> > > +		if (last == ';' && !isspace(c)) {
> > > +			*pos++ = ' ';
> > > +			len--;
> > > +		}
> > > +
> > > +		if (len > 0) {
> > > +			*pos++ = c;
> > > +			len--;
> > > +		}
> > > +
> > > +		last = c;
> > > +	}
> > 
> > nit: This loop can be simpler, because we are sure fixed has enough length;
> > 
> > /* insert a space after ';' if there is no space. */
> > while(*args) {
> > 	*pos = *args++;
> > 	if (*pos++ == ';' && !isspace(*args))
> > 		*pos++ = ' ';
> > }
> > 
> 
> I was worried that if count_semis_no_space() ever had different logic
> (maybe after this commit) that it could cause an overflow if the count
> was wrong, etc.
> 
> I don't have an issue making it shorter, but I was trying to be more on
> the safe side, since this isn't a fast path (event register).

OK, anyway current code looks correct. But note that I don't think
"pos++; len--;" is safer, since it is not atomic. This pattern
easily loose "len--;" in my experience. So please carefully use it ;)

> 
> > > +
> > > +	/*
> > > +	 * len is the length of the copy excluding the null.
> > > +	 * This ensures we always have room for a null.
> > > +	 */
> > > +	*pos = '\0';
> > > +
> > > +	return fixed;
> > > +}
> > > +
> > > +static char **user_event_argv_split(char *args, int *argc)
> > > +{
> > > +	/* Count how many ';' without a trailing space */
> > > +	int count = count_semis_no_space(args);
> > > +
> > > +	if (count) {
> > 
> > nit: it is better to exit fast, so 
> > 
> > 	if (!count)
> > 		return argv_split(GFP_KERNEL, args, argc);
> > 
> > 	...
> 
> Sure, will fix in a v2.
> 
> > 
> > Thank you,
> > 
> > OT: BTW, can this also simplify synthetic events?
> > 
> 
> I'm not sure, I'll check when I have some time. I want to get this fix
> in sooner rather than later.

Ah, nevermind. Synthetic event parses the field by strsep(';') first
and argv_split(). So it does not have this issue.

Thank you,

> 
> Thanks,
> -Beau
> 
> > > +		/* We must fixup 'field;field' to 'field; field' */
> > > +		char *fixed = fix_semis_no_space(args, count);
> > > +		char **split;
> > > +
> > > +		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;
> > > +	}
> > > +
> > > +	/* No fixup is required */
> > > +	return argv_split(GFP_KERNEL, args, argc);
> > > +}
> > > +
> > >  /*
> > >   * 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 +2098,7 @@ 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
> > > 
> > 
> > 
> > -- 
> > Masami Hiramatsu (Google) <mhiramat@kernel.org>


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

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

[Beau Belgrave]

On Sat, Apr 20, 2024 at 09:50:52PM +0900, Masami Hiramatsu wrote:
> On Fri, 19 Apr 2024 14:13:34 -0700
> Beau Belgrave <beaub@linux.microsoft.com> wrote:
> 
> > On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote:
> > > On Tue, 16 Apr 2024 22:41:01 +0000
> > > Beau Belgrave <beaub@linux.microsoft.com> wrote:

*SNIP*

> > > nit: This loop can be simpler, because we are sure fixed has enough length;
> > > 
> > > /* insert a space after ';' if there is no space. */
> > > while(*args) {
> > > 	*pos = *args++;
> > > 	if (*pos++ == ';' && !isspace(*args))
> > > 		*pos++ = ' ';
> > > }
> > > 
> > 
> > I was worried that if count_semis_no_space() ever had different logic
> > (maybe after this commit) that it could cause an overflow if the count
> > was wrong, etc.
> > 
> > I don't have an issue making it shorter, but I was trying to be more on
> > the safe side, since this isn't a fast path (event register).
> 
> OK, anyway current code looks correct. But note that I don't think
> "pos++; len--;" is safer, since it is not atomic. This pattern
> easily loose "len--;" in my experience. So please carefully use it ;)
> 

I'll stick with your loop. Perhaps others will chime in on the v2 and
state a stronger opinion.

You scared me with the atomic comment, I went back and looked at all the
paths for this. In the user_events IOCTL the buffer is copied from user
to kernel, so it cannot change (and no other threads access it). I also
checked trace_parse_run_command() which is the same. So at least in this
context the non-atomic part is OK.

> > 
> > > > +
> > > > +	/*
> > > > +	 * len is the length of the copy excluding the null.
> > > > +	 * This ensures we always have room for a null.
> > > > +	 */
> > > > +	*pos = '\0';
> > > > +
> > > > +	return fixed;
> > > > +}
> > > > +
> > > > +static char **user_event_argv_split(char *args, int *argc)
> > > > +{
> > > > +	/* Count how many ';' without a trailing space */
> > > > +	int count = count_semis_no_space(args);
> > > > +
> > > > +	if (count) {
> > > 
> > > nit: it is better to exit fast, so 
> > > 
> > > 	if (!count)
> > > 		return argv_split(GFP_KERNEL, args, argc);
> > > 
> > > 	...
> > 
> > Sure, will fix in a v2.
> > 
> > > 
> > > Thank you,
> > > 
> > > OT: BTW, can this also simplify synthetic events?
> > > 
> > 
> > I'm not sure, I'll check when I have some time. I want to get this fix
> > in sooner rather than later.
> 
> Ah, nevermind. Synthetic event parses the field by strsep(';') first
> and argv_split(). So it does not have this issue.
> 

Ok, seems unrelated. Thanks for checking.

Thanks,
-Beau

> Thank you,
> 
> > 
> > Thanks,
> > -Beau
> > 

*SNIP* 

> > > Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

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

[Masami Hiramatsu]

On Mon, 22 Apr 2024 14:55:25 -0700
Beau Belgrave <beaub@linux.microsoft.com> wrote:

> On Sat, Apr 20, 2024 at 09:50:52PM +0900, Masami Hiramatsu wrote:
> > On Fri, 19 Apr 2024 14:13:34 -0700
> > Beau Belgrave <beaub@linux.microsoft.com> wrote:
> > 
> > > On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote:
> > > > On Tue, 16 Apr 2024 22:41:01 +0000
> > > > Beau Belgrave <beaub@linux.microsoft.com> wrote:
> 
> *SNIP*
> 
> > > > nit: This loop can be simpler, because we are sure fixed has enough length;
> > > > 
> > > > /* insert a space after ';' if there is no space. */
> > > > while(*args) {
> > > > 	*pos = *args++;
> > > > 	if (*pos++ == ';' && !isspace(*args))
> > > > 		*pos++ = ' ';
> > > > }
> > > > 
> > > 
> > > I was worried that if count_semis_no_space() ever had different logic
> > > (maybe after this commit) that it could cause an overflow if the count
> > > was wrong, etc.
> > > 
> > > I don't have an issue making it shorter, but I was trying to be more on
> > > the safe side, since this isn't a fast path (event register).
> > 
> > OK, anyway current code looks correct. But note that I don't think
> > "pos++; len--;" is safer, since it is not atomic. This pattern
> > easily loose "len--;" in my experience. So please carefully use it ;)
> > 
> 
> I'll stick with your loop. Perhaps others will chime in on the v2 and
> state a stronger opinion.
> 
> You scared me with the atomic comment, I went back and looked at all the
> paths for this. In the user_events IOCTL the buffer is copied from user
> to kernel, so it cannot change (and no other threads access it). I also
> checked trace_parse_run_command() which is the same. So at least in this
> context the non-atomic part is OK.

Oh, sorry if I scared you. I've seen bugs get introduced into loops like
this many times (while updating the code), so I try to keep it simple.
I'm sure that your code has no bugs.

Thank you,

-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>