On Tue, 16 Apr 2024 22:41:01 +0000 Beau Belgrave <be...@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 <be...@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) <mhira...@kernel.org>