From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: [PATCH printk-rework 01/14] printk: limit second loop of syslog_print_all
Date: Thu, 18 Feb 2021 09:18:04 +0100 [thread overview]
Message-ID: <20210218081817.28849-2-john.ogness@linutronix.de> (raw)
In-Reply-To: <20210218081817.28849-1-john.ogness@linutronix.de>
The second loop of syslog_print_all() subtracts lengths that were
added in the first loop. With commit b031a684bfd0 ("printk: remove
logbuf_lock writer-protection of ringbuffer") it is possible that
records are (over)written during syslog_print_all(). This allows the
possibility of the second loop subtracting lengths that were never
added in the first loop.
This situation can result in syslog_print_all() filling the buffer
starting from a later record, even though there may have been room
to fit the earlier record(s) as well.
Fixes: b031a684bfd0 ("printk: remove logbuf_lock writer-protection of ringbuffer")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c7239d169bbe..411787b900ac 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1495,6 +1495,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
struct printk_info info;
unsigned int line_count;
struct printk_record r;
+ u64 max_seq;
char *text;
int len = 0;
u64 seq;
@@ -1513,9 +1514,15 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
len += get_record_print_text_size(&info, line_count, true, time);
+ /*
+ * Set an upper bound for the next loop to avoid subtracting lengths
+ * that were never added.
+ */
+ max_seq = seq;
+
/* move first record forward until length fits into the buffer */
prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
- if (len <= size)
+ if (len <= size || info.seq >= max_seq)
break;
len -= get_record_print_text_size(&info, line_count, true, time);
}
--
2.20.1
next prev parent reply other threads:[~2021-02-18 9:40 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 8:18 [PATCH printk-rework 00/14] printk: remove logbuf_lock John Ogness
2021-02-18 8:18 ` John Ogness [this message]
2021-02-18 16:15 ` [PATCH printk-rework 01/14] printk: limit second loop of syslog_print_all Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 02/14] printk: kmsg_dump: remove unused fields John Ogness
2021-02-18 16:18 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 03/14] printk: refactor kmsg_dump_get_buffer() John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 04/14] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code John Ogness
2021-02-19 12:28 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 05/14] printk: introduce CONSOLE_LOG_MAX for improved multi-line support John Ogness
2021-02-19 12:44 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 06/14] printk: use seqcount_latch for clear_seq John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 07/14] printk: use atomic64_t for devkmsg_user.seq John Ogness
2021-02-19 12:59 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 08/14] printk: add syslog_lock John Ogness
2021-02-19 13:30 ` Petr Mladek
2021-02-19 14:45 ` John Ogness
2021-02-19 16:33 ` John Ogness
2021-02-21 21:39 ` Helge Deller
2021-02-22 16:28 ` Petr Mladek
2021-02-23 12:22 ` Helge Deller
2021-02-23 14:23 ` Petr Mladek
2021-02-23 14:45 ` Helge Deller
2021-02-22 16:05 ` Petr Mladek
2021-02-22 16:43 ` John Ogness
2021-02-23 14:38 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 09/14] printk: introduce a kmsg_dump iterator John Ogness
2021-02-19 15:56 ` Petr Mladek
2021-02-19 16:50 ` Michael Kelley
2021-02-19 17:57 ` synchronization model: was: " Petr Mladek
2021-02-24 12:27 ` John Ogness
2021-02-24 15:40 ` John Ogness
2021-02-25 12:33 ` Petr Mladek
2021-02-26 8:36 ` John Ogness
2021-02-26 9:48 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 10/14] um: synchronize kmsg_dumper John Ogness
2021-02-18 8:18 ` [PATCH printk-rework 11/14] printk: remove logbuf_lock John Ogness
2021-02-23 11:44 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 12/14] printk: kmsg_dump: remove _nolock() variants John Ogness
2021-02-23 11:51 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 13/14] printk: kmsg_dump: use kmsg_dump_rewind John Ogness
2021-02-23 11:53 ` Petr Mladek
2021-02-18 8:18 ` [PATCH printk-rework 14/14] printk: console: remove unnecessary safe buffer usage John Ogness
2021-02-23 12:55 ` Petr Mladek
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=20210218081817.28849-2-john.ogness@linutronix.de \
--to=john.ogness@linutronix.de \
--cc=linux-kernel@vger.kernel.org \
--cc=pmladek@suse.com \
--cc=rostedt@goodmis.org \
--cc=sergey.senozhatsky.work@gmail.com \
--cc=sergey.senozhatsky@gmail.com \
--cc=tglx@linutronix.de \
/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).