diff options
author | Elazar Leibovich <elazar@lightbitslabs.com> | 2018-12-31 13:58:37 +0200 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-25 18:22:11 +0200 |
commit | 95142e28042b1f51cbeec81488799d163eb67242 (patch) | |
tree | 780c8c9ba90e0708883ba660002c08c824a9ceed | |
parent | 9dba717a81560b6164582c3ebb2b94d4ae08c12e (diff) |
tracing: Fix partial reading of trace event's id file
commit cbe08bcbbe787315c425dde284dcb715cfbf3f39 upstream.
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | kernel/trace/trace_events.c | 3 |
1 files changed, 0 insertions, 3 deletions
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 5b3b0c3c8a47..d910e36c34b5 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1318,9 +1318,6 @@ 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; |