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50 lines
1.8 KiB
Diff
50 lines
1.8 KiB
Diff
From: John Ogness <john.ogness@linutronix.de>
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Date: Wed, 17 Feb 2021 16:15:31 +0100
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Subject: [PATCH 02/28] printk: limit second loop of syslog_print_all
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The second loop of syslog_print_all() subtracts lengths that were
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added in the first loop. With commit b031a684bfd0 ("printk: remove
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logbuf_lock writer-protection of ringbuffer") it is possible that
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records are (over)written during syslog_print_all(). This allows the
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possibility of the second loop subtracting lengths that were never
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added in the first loop.
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This situation can result in syslog_print_all() filling the buffer
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starting from a later record, even though there may have been room
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to fit the earlier record(s) as well.
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Fixes: b031a684bfd0 ("printk: remove logbuf_lock writer-protection of ringbuffer")
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Reviewed-by: Petr Mladek <pmladek@suse.com>
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---
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kernel/printk/printk.c | 9 ++++++++-
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1 file changed, 8 insertions(+), 1 deletion(-)
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -1494,6 +1494,7 @@ static int syslog_print_all(char __user
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struct printk_info info;
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unsigned int line_count;
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struct printk_record r;
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+ u64 max_seq;
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char *text;
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int len = 0;
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u64 seq;
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@@ -1512,9 +1513,15 @@ static int syslog_print_all(char __user
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prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
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len += get_record_print_text_size(&info, line_count, true, time);
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+ /*
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+ * Set an upper bound for the next loop to avoid subtracting lengths
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+ * that were never added.
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+ */
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+ max_seq = seq;
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+
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/* move first record forward until length fits into the buffer */
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prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
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- if (len <= size)
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+ if (len <= size || info.seq >= max_seq)
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break;
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len -= get_record_print_text_size(&info, line_count, true, time);
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}
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