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 <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) +{ + 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