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Commit d43ff430 authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds
Browse files

printk: guard the amount written per line by devkmsg_read() 



This patchset updates netconsole so that it can emit messages with the
same header as used in /dev/kmsg which gives neconsole receiver full log
information which enables things like structured logging and detection
of lost messages.

This patch (of 7):

devkmsg_read() uses 8k buffer and assumes that the formatted output
message won't overrun which seems safe given LOG_LINE_MAX, the current use
of dict and the escaping method being used; however, we're planning to use
devkmsg formatting wider and accounting for the buffer size properly isn't
that complicated.

This patch defines CONSOLE_EXT_LOG_MAX as 8192 and updates devkmsg_read()
so that it limits output accordingly.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: David Miller <davem@davemloft.net>
Cc: Kay Sievers <kay@vrfy.org>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.cz>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4ae555a5

include/linux/printk.h

+2 −0
Original line number Diff line number Diff line
@@ -30,6 +30,8 @@ static inline const char *printk_skip_level(const char *buffer) 
	return buffer;

}



#define CONSOLE_EXT_LOG_MAX	8192



/* printk's without a loglevel use this.. */

#define MESSAGE_LOGLEVEL_DEFAULT CONFIG_MESSAGE_LOGLEVEL_DEFAULT

kernel/printk/printk.c

+22 −12
Original line number Diff line number Diff line
@@ -505,6 +505,11 @@ int check_syslog_permissions(int type, bool from_file) 
	return security_syslog(type);

}



static void append_char(char **pp, char *e, char c)

{

	if (*pp < e)

		*(*pp)++ = c;

}



/* /dev/kmsg - userspace message inject/listen interface */

struct devkmsg_user {
@@ -512,7 +517,7 @@ struct devkmsg_user { 
	u32 idx;

	enum log_flags prev;

	struct mutex lock;

	char buf[8192];

	char buf[CONSOLE_EXT_LOG_MAX];

};



static ssize_t devkmsg_write(struct kiocb *iocb, struct iov_iter *from)
@@ -570,6 +575,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
{

	struct devkmsg_user *user = file->private_data;

	struct printk_log *msg;

	char *p, *e;

	u64 ts_usec;

	size_t i;

	char cont = '-';
@@ -579,6 +585,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
	if (!user)

		return -EBADF;



	p = user->buf;

	e = user->buf + sizeof(user->buf);



	ret = mutex_lock_interruptible(&user->lock);

	if (ret)

		return ret;
@@ -625,7 +634,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
		 ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))

		cont = '+';



	len = sprintf(user->buf, "%u,%llu,%llu,%c;",

	p += scnprintf(p, e - p, "%u,%llu,%llu,%c;",

		       (msg->facility << 3) | msg->level,

		       user->seq, ts_usec, cont);

	user->prev = msg->flags;
@@ -635,11 +644,11 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
		unsigned char c = log_text(msg)[i];



		if (c < ' ' || c >= 127 || c == '\\')

			len += sprintf(user->buf + len, "\\x%02x", c);

			p += scnprintf(p, e - p, "\\x%02x", c);

		else

			user->buf[len++] = c;

			append_char(&p, e, c);

	}

	user->buf[len++] = '\n';

	append_char(&p, e, '\n');



	if (msg->dict_len) {

		bool line = true;
@@ -648,30 +657,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
			unsigned char c = log_dict(msg)[i];



			if (line) {

				user->buf[len++] = ' ';

				append_char(&p, e, ' ');

				line = false;

			}



			if (c == '\0') {

				user->buf[len++] = '\n';

				append_char(&p, e, '\n');

				line = true;

				continue;

			}



			if (c < ' ' || c >= 127 || c == '\\') {

				len += sprintf(user->buf + len, "\\x%02x", c);

				p += scnprintf(p, e - p, "\\x%02x", c);

				continue;

			}



			user->buf[len++] = c;

			append_char(&p, e, c);

		}

		user->buf[len++] = '\n';

		append_char(&p, e, '\n');

	}



	user->idx = log_next(user->idx);

	user->seq++;

	raw_spin_unlock_irq(&logbuf_lock);



	len = p - user->buf;

	if (len > count) {

		ret = -EINVAL;

		goto out;