From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 74DC0625; Sat, 20 Apr 2024 12:50:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713617456; cv=none; b=kNOQ2QB30uCfT45LTjOOsM/mMVqDZG2zN8m545pAfMF1PJ4lXYPL/0vfnb611S1QhnwBzvEWG0C7Bfj/lfxSjOkvSASCzYc+hQizGbD0MUgr5rDJyLSW0K3H57rt3PWvWH8N18Pva+zdhSqJVX5g3i9Qk9Lqv5sFN/yUbukFL/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713617456; c=relaxed/simple; bh=289IG/8ie1lhiRC5p5kwvp2q+FCe7+CmmeFkid4uKM0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=J8gBJhgreDwTr9oi8Bks1TlxKUz55AKTVjqXyTD+oOxHCj51f5/NGceEOCPnV7i7rPZSpB2YR4TOlLcQbGeiEOvxQeCaBeUU96KYIyObAbN/xYr4Uy69Emndjfh43KA7410xEGvJeqFeZuDQNNfyFa7ZDnrfwBEY7HDiW7IBo9U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZWiV0WbE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ZWiV0WbE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 52EF9C072AA; Sat, 20 Apr 2024 12:50:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713617455; bh=289IG/8ie1lhiRC5p5kwvp2q+FCe7+CmmeFkid4uKM0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ZWiV0WbEPE20fapCabZLXpoPHMdlaE5IgIOh+Ck36yRWt+qtmO+zwqLRHoAAGLSYk f+gdziBs0V+HxyWLlzPgQSBSHa+S7dHnD172p5cEka1ICZe89FiMsHP/cQ2HpSuQ2S PBz8NrHCoKV+7+TnJXCD4e6gawRah21Kww1JroVl6ORRjTllqiZbmaMmItzXdxcLGi NjArU+gR7QHSNgoQ0ZiZB9j/dpjIU16VeF74ReuvHhUXShP2+/quVK3NUDKkl9LjOr Fo4GIQJgZNZx/Rl+KuvkqG5ILIOO2+cyXGqM+rLYSYjhH9yrOomZGy1jEuttr14Mmg jWQ7PM2odQSgw== Date: Sat, 20 Apr 2024 21:50:52 +0900 From: Masami Hiramatsu (Google) To: Beau Belgrave 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: <20240420215052.1f806c8acb5f99ec2f63945c@kernel.org> In-Reply-To: <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> <20240419211334.GA7774-beaub@linux.microsoft.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit On Fri, 19 Apr 2024 14:13:34 -0700 Beau Belgrave 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 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). 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) -- Masami Hiramatsu (Google)