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From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 3 Mar 2021 11:15:16 +0100
Subject: [PATCH 03/29] printk: limit second loop of syslog_print_all
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>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210303101528.29901-4-john.ogness@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1494,6 +1494,7 @@ static int syslog_print_all(char __user
struct printk_info info;
unsigned int line_count;
struct printk_record r;
+ u64 max_seq;
char *text;
int len = 0;
u64 seq;
@@ -1512,9 +1513,15 @@ static int syslog_print_all(char __user
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);
}
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