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(c-76-135-27-212.hsd1.wa.comcast.net [76.135.27.212]) by linux.microsoft.com (Postfix) with ESMTPSA id C44D620FDC4B; Fri, 19 Apr 2024 14:13:40 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com C44D620FDC4B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1713561220; bh=XE0uXoNgtxaWLEQbxNxQNdOcqHe9iSSF1gbTqedCfmc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cuEjqFg4dJDkNgNbzNK76wVSFkgIGMb3iAw//dEEgp9GwYszBB9YeKAONXAKwQrIE ZbXNd419UkKbywo2Fbm6yYUuTKOcM7iHmgNqrMAKnYecX/dVbMhJ1jQ52xra354K77 KhBHDRu/QjWB+xGPxU5igmsVJAEiIVLHN107LPek= Date: Fri, 19 Apr 2024 14:13:34 -0700 From: Beau Belgrave To: Masami Hiramatsu Cc: rostedt@goodmis.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, dcook@linux.microsoft.com Subject: Re: [PATCH 1/2] tracing/user_events: Fix non-spaced field matching Message-ID: <20240419211334.GA7774-beaub@linux.microsoft.com> References: <20240416224102.734-1-beaub@linux.microsoft.com> <20240416224102.734-2-beaub@linux.microsoft.com> <20240419113305.7b0ae2b11395eec16b5c15b6@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240419113305.7b0ae2b11395eec16b5c15b6@kernel.org> On Fri, Apr 19, 2024 at 11:33:05AM +0900, Masami Hiramatsu wrote: > On Tue, 16 Apr 2024 22:41:01 +0000 > Beau Belgrave 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 > > --- > > 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)