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Commit eb02dac9 authored by Kay Sievers's avatar Kay Sievers Committed by Greg Kroah-Hartman
Browse files

kmsg: /proc/kmsg - support reading of partial log records 

Restore support for partial reads of any size on /proc/kmsg, in case the
supplied read buffer is smaller than the record size.

Some people seem to think is is ia good idea to run:
  $ dd if=/proc/kmsg bs=1 of=...
as a klog bridge.

Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=44211


Reported-by: default avatarJukka Ollila <jiiksteri@gmail.com>
Signed-off-by: default avatarKay Sievers <kay@vrfy.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 68b6507d

kernel/printk.c

+20 −8
Original line number Diff line number Diff line
@@ -217,6 +217,7 @@ static DEFINE_RAW_SPINLOCK(logbuf_lock); 
/* the next printk record to read by syslog(READ) or /proc/kmsg */

static u64 syslog_seq;

static u32 syslog_idx;

static size_t syslog_partial;



/* index and sequence number of the first record stored in the buffer */

static u64 log_first_seq;
@@ -890,22 +891,33 @@ static int syslog_print(char __user *buf, int size) 


	while (size > 0) {

		size_t n;

		size_t skip;



		raw_spin_lock_irq(&logbuf_lock);

		if (syslog_seq < log_first_seq) {

			/* messages are gone, move to first one */

			syslog_seq = log_first_seq;

			syslog_idx = log_first_idx;

			syslog_partial = 0;

		}

		if (syslog_seq == log_next_seq) {

			raw_spin_unlock_irq(&logbuf_lock);

			break;

		}



		skip = syslog_partial;

		msg = log_from_idx(syslog_idx);

		n = msg_print_text(msg, true, text, LOG_LINE_MAX);

		if (n <= size) {

		if (n - syslog_partial <= size) {

			/* message fits into buffer, move forward */

			syslog_idx = log_next(syslog_idx);

			syslog_seq++;

			n -= syslog_partial;

			syslog_partial = 0;

		} else if (!len){

			/* partial read(), remember position */

			n = size;

			syslog_partial += n;

		} else

			n = 0;

		raw_spin_unlock_irq(&logbuf_lock);
@@ -913,17 +925,15 @@ static int syslog_print(char __user *buf, int size) 
		if (!n)

			break;



		len += n;

		size -= n;

		buf += n;

		n = copy_to_user(buf - n, text, n);



		if (n) {

			len -= n;

		if (copy_to_user(buf, text + skip, n)) {

			if (!len)

				len = -EFAULT;

			break;

		}



		len += n;

		size -= n;

		buf += n;

	}



	kfree(text);
@@ -1107,6 +1117,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) 
			/* messages are gone, move to first one */

			syslog_seq = log_first_seq;

			syslog_idx = log_first_idx;

			syslog_partial = 0;

		}

		if (from_file) {

			/*
@@ -1129,6 +1140,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file) 
				idx = log_next(idx);

				seq++;

			}

			error -= syslog_partial;

		}

		raw_spin_unlock_irq(&logbuf_lock);

		break;