From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Orit Wasserman <orit.was@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>,
stable@vger.kernel.org,
Elazar Leibovich <elazar@lightbitslabs.com>
Subject: [for-next][PATCH 11/13] tracing: Fix partial reading of trace events id file
Date: Wed, 08 May 2019 16:24:38 -0400 [thread overview]
Message-ID: <20190508202453.536550511@goodmis.org> (raw)
In-Reply-To: 20190508202427.252736423@goodmis.org
From: Elazar Leibovich <elazar@lightbitslabs.com>
When reading only part of the id file, the ppos isn't tracked correctly.
This is taken care by simple_read_from_buffer.
Reading a single byte, and then the next byte would result EOF.
While this seems like not a big deal, this breaks abstractions that
reads information from files unbuffered. See for example
https://github.com/golang/go/issues/29399
This code was mentioned as problematic in
commit cd458ba9d5a5
("tracing: Do not (ab)use trace_seq in event_id_read()")
An example C code that show this bug is:
#include <stdio.h>
#include <stdint.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main(int argc, char **argv) {
if (argc < 2)
return 1;
int fd = open(argv[1], O_RDONLY);
char c;
read(fd, &c, 1);
printf("First %c\n", c);
read(fd, &c, 1);
printf("Second %c\n", c);
}
Then run with, e.g.
sudo ./a.out /sys/kernel/debug/tracing/events/tcp/tcp_set_state/id
You'll notice you're getting the first character twice, instead of the
first two characters in the id file.
Link: http://lkml.kernel.org/r/20181231115837.4932-1-elazar@lightbitslabs.com
Cc: Orit Wasserman <orit.was@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 23725aeeab10b ("ftrace: provide an id file for each event")
Signed-off-by: Elazar Leibovich <elazar@lightbitslabs.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_events.c | 3 ---
1 file changed, 3 deletions(-)
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 81c038ed6cee..0ce3db67f556 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1319,9 +1319,6 @@ event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
char buf[32];
int len;
- if (*ppos)
- return 0;
-
if (unlikely(!id))
return -ENODEV;
--
2.20.1
next prev parent reply other threads:[~2019-05-08 20:25 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-08 20:24 [for-next][PATCH 00/13] tracing: Some more last minute changes and fixes Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 01/13] x86_64: Add gap to int3 to allow for call emulation Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 02/13] x86_64: Allow breakpoints to emulate call instructions Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 03/13] ftrace/x86_64: Emulate call function while updating in breakpoint handler Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 04/13] tracing: uprobes: Re-enable $comm support for uprobe events Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 05/13] tracing: probeevent: Do not accumulate on ret variable Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 06/13] tracing: probeevent: Fix to make the type of $comm string Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 07/13] ring-buffer: Fix mispelling of Calculate Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 08/13] tracing: Eliminate const char[] auto variables Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 09/13] tracing: Fix white space issues in parse_pred() function Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 10/13] tracing: Allow RCU to run between postponed startup tests Steven Rostedt
2019-05-08 20:24 ` Steven Rostedt [this message]
2019-05-08 20:24 ` [for-next][PATCH 12/13] tracing: Replace kzalloc with kcalloc Steven Rostedt
2019-05-08 20:24 ` [for-next][PATCH 13/13] tracing: Fix documentation about disabling options using trace_options Steven Rostedt
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190508202453.536550511@goodmis.org \
--to=rostedt@goodmis.org \
--cc=akpm@linux-foundation.org \
--cc=elazar@lightbitslabs.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=orit.was@gmail.com \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).