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
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(-)
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
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(+)
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, ®));
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, ®));
+ 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
On Tue, 23 Apr 2024 16:23:37 +0000
Beau Belgrave <[email protected]> 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 <[email protected]>
> ---
> 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;
> +}
> +
On Thu, May 02, 2024 at 05:16:34PM -0400, Steven Rostedt wrote:
> On Tue, 23 Apr 2024 16:23:37 +0000
> Beau Belgrave <[email protected]> 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 <[email protected]>
> > ---
> > 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;
> > +}
> > +
On Thu, 2 May 2024 15:58:53 -0700
Beau Belgrave <[email protected]> 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