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Elazar Leibovich cbe08bcbbe tracing: Fix partial reading of trace event's id file 
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 cd458ba9d5
("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: 23725aeeab ("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>
2019-05-08 12:15:12 -04:00
arch ftrace/x86_64: Emulate call function while updating in breakpoint handler 2019-05-08 12:14:59 -04:00
block blk-mq: fix sbitmap ws_active for shared tags 2019-03-25 13:05:47 -06:00
certs kexec, KEYS: Make use of platform keyring for signature verify 2019-02-04 17:34:07 -05:00
crypto lib/lzo: separate lzo-rle from lzo 2019-03-07 18:32:03 -08:00
Documentation tracing: Add tracing/error_log Documentation 2019-04-08 09:22:50 -04:00
drivers dmaengine-5.10-rc3 2019-03-31 07:42:39 -07:00
fs Merge branch 'akpm' (patches from Andrew) 2019-03-29 16:02:28 -07:00
include function_graph: Place ftrace_graph_entry_stub() prototype in include/linux/ftrace.h 2019-04-29 17:17:22 -04:00
init init/main: add checks for the return value of memblock_alloc*() 2019-03-12 10:04:02 -07:00
ipc Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 14:08:19 -07:00
kernel tracing: Fix partial reading of trace event's id file 2019-05-08 12:15:12 -04:00
lib for-linus-20190329 2019-03-29 14:43:07 -07:00
LICENSES LICENSES: Add GCC runtime library exception text 2019-01-16 14:54:15 -07:00
mm mm/migrate.c: add missing flush_dcache_page for non-mapped page migrate 2019-03-29 10:01:37 -07:00
net A patch to avoid choking on multipage bvecs in the messenger and 2019-03-29 14:41:09 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-03-11 08:54:01 -07:00
scripts Merge branch 'akpm' (patches from Andrew) 2019-03-29 16:02:28 -07:00
security LSM: Revive CONFIG_DEFAULT_SECURITY_* for "make oldconfig" 2019-03-29 14:08:49 -07:00
sound sound fixes for 5.1-rc3 2019-03-29 14:53:33 -07:00
tools selftests/ftrace: Add tracing/error_log testcase 2019-04-08 09:22:50 -04:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM/ARM fixes for 5.1 2019-03-28 19:07:30 +01:00
.clang-format Merge branch 'work.iov_iter' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 13:43:42 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap mailmap: add Changbin Du 2019-03-29 10:01:37 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Char/Misc driver patches for 5.1-rc1 2019-03-06 14:18:59 -08:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-03-31 07:48:58 -07:00
Makefile Linux 5.1-rc3 2019-03-31 14:39:29 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.