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
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
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 | 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
On Tue, 16 Apr 2024 22:41:01 +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
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 <[email protected]>
> ---
> 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) <[email protected]>
On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote:
> On Tue, 16 Apr 2024 22:41:01 +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
>
> 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 <[email protected]>
> > ---
> > 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) <[email protected]>
On Fri, 19 Apr 2024 14:13:34 -0700
Beau Belgrave <[email protected]> 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 <[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
> >
> > 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 <[email protected]>
> > > ---
> > > 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) <[email protected]>
--
Masami Hiramatsu (Google) <[email protected]>
On Sat, Apr 20, 2024 at 09:50:52PM +0900, Masami Hiramatsu wrote:
> On Fri, 19 Apr 2024 14:13:34 -0700
> Beau Belgrave <[email protected]> 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 <[email protected]> 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) <[email protected]>
>
>
> --
> Masami Hiramatsu (Google) <[email protected]>
On Mon, 22 Apr 2024 14:55:25 -0700
Beau Belgrave <[email protected]> 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 <[email protected]> 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 <[email protected]> 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) <[email protected]>