Commit 3fa10cc8 authored Apr 26, 2012 by Jiri Slaby Committed by Greg Kroah-Hartman Apr 29, 2012

TTY: n_tty, do not dereference user buffer



copy_from_read_buf currently copies data to a user buffer and then
checks if the data is single EOF. But it checks it by accessing the
user buffer. First, the buffer may be changed by other threads of the
user program already. Second, it accesses the buffer without any
checks. It might be write-only for example.

Fix this by inspecting contents of the tty (kernel) buffer instead.
Note that "n == 1" is necessary, but not sufficient. But we check
later that there is nothing left by "!tty->read_cnt" condition.

There is still an issue with the current code that EOF being wrapped
to the start of the circular buffer will result in an inappropriate
losing of the EOF character. But this is not intended to be fixed by
this patch.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Emil Goode <emilgoode@gmail.com>
Cc: Howard Chu <hyc@symas.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 5d1a33fa

drivers/tty/n_tty.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -1630,6 +1630,7 @@ static int copy_from_read_buf(struct tty_struct *tty,
		int retval;
		size_t n;
		unsigned long flags;
		bool is_eof;

		retval = 0;
		spin_lock_irqsave(&tty->read_lock, flags);
		@@ -1639,15 +1640,15 @@ static int copy_from_read_buf(struct tty_struct *tty,
		if (n) {
		retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
		n -= retval;
		is_eof = n == 1 &&
		tty->read_buf[tty->read_tail] == EOF_CHAR(tty);
		tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
		spin_lock_irqsave(&tty->read_lock, flags);
		tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
		tty->read_cnt -= n;
		/* Turn single EOF into zero-length read */
		if (L_EXTPROC(tty) && tty->icanon && n == 1) {
		if (!tty->read_cnt && (*b)[n-1] == EOF_CHAR(tty))
		n--;
		}
		if (L_EXTPROC(tty) && tty->icanon && is_eof && !tty->read_cnt)
		n = 0;
		spin_unlock_irqrestore(&tty->read_lock, flags);
		*b += n;
		*nr -= n;

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