CVE-2017-2636 Race condition access to n_hdlc.tbuf causes double free in n_hdlc_release (rhbz 1430049)
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Laura Abbott
parent
8e4bbb22f1
commit
a78a24cb93
311
0001-tty-n_hdlc-get-rid-of-racy-n_hdlc.tbuf.patch
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311
0001-tty-n_hdlc-get-rid-of-racy-n_hdlc.tbuf.patch
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@ -0,0 +1,311 @@
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From 1dea7a8061ad9212f4464464a80d0dcd477eceab Mon Sep 17 00:00:00 2001
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From: Alexander Popov <alex.popov@linux.com>
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Date: Tue, 28 Feb 2017 19:28:54 +0300
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Subject: [PATCH 1/1] tty: n_hdlc: get rid of racy n_hdlc.tbuf
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Currently N_HDLC line discipline uses a self-made singly linked list for
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data buffers and has n_hdlc.tbuf pointer for buffer retransmitting after
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an error.
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The commit be10eb7589337e5defbe214dae038a53dd21add8
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("tty: n_hdlc add buffer flushing") introduced racy access to n_hdlc.tbuf.
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After tx error concurrent flush_tx_queue() and n_hdlc_send_frames() can put
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one data buffer to tx_free_buf_list twice. That causes double free in
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n_hdlc_release().
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Let's use standard kernel linked list and get rid of n_hdlc.tbuf:
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in case of tx error put current data buffer after the head of tx_buf_list.
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Signed-off-by: Alexander Popov <alex.popov@linux.com>
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---
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drivers/tty/n_hdlc.c | 132 +++++++++++++++++++++++++++------------------------
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1 file changed, 69 insertions(+), 63 deletions(-)
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diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
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index eb27883..728c824 100644
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--- a/drivers/tty/n_hdlc.c
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+++ b/drivers/tty/n_hdlc.c
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@@ -114,7 +114,7 @@
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#define DEFAULT_TX_BUF_COUNT 3
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struct n_hdlc_buf {
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- struct n_hdlc_buf *link;
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+ struct list_head list_item;
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int count;
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char buf[1];
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};
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@@ -122,8 +122,7 @@ struct n_hdlc_buf {
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#define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
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struct n_hdlc_buf_list {
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- struct n_hdlc_buf *head;
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- struct n_hdlc_buf *tail;
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+ struct list_head list;
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int count;
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spinlock_t spinlock;
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};
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@@ -136,7 +135,6 @@ struct n_hdlc_buf_list {
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* @backup_tty - TTY to use if tty gets closed
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* @tbusy - reentrancy flag for tx wakeup code
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* @woke_up - FIXME: describe this field
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- * @tbuf - currently transmitting tx buffer
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* @tx_buf_list - list of pending transmit frame buffers
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* @rx_buf_list - list of received frame buffers
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* @tx_free_buf_list - list unused transmit frame buffers
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@@ -149,7 +147,6 @@ struct n_hdlc {
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struct tty_struct *backup_tty;
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int tbusy;
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int woke_up;
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- struct n_hdlc_buf *tbuf;
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struct n_hdlc_buf_list tx_buf_list;
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struct n_hdlc_buf_list rx_buf_list;
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struct n_hdlc_buf_list tx_free_buf_list;
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@@ -159,6 +156,8 @@ struct n_hdlc {
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/*
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* HDLC buffer list manipulation functions
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*/
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+static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
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+ struct n_hdlc_buf *buf);
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static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
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struct n_hdlc_buf *buf);
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static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *list);
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@@ -208,16 +207,9 @@ static void flush_tx_queue(struct tty_struct *tty)
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{
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struct n_hdlc *n_hdlc = tty2n_hdlc(tty);
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struct n_hdlc_buf *buf;
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- unsigned long flags;
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while ((buf = n_hdlc_buf_get(&n_hdlc->tx_buf_list)))
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n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, buf);
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- spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock, flags);
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- if (n_hdlc->tbuf) {
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- n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, n_hdlc->tbuf);
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- n_hdlc->tbuf = NULL;
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- }
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- spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
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}
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static struct tty_ldisc_ops n_hdlc_ldisc = {
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@@ -283,7 +275,6 @@ static void n_hdlc_release(struct n_hdlc *n_hdlc)
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} else
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break;
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}
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- kfree(n_hdlc->tbuf);
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kfree(n_hdlc);
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} /* end of n_hdlc_release() */
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@@ -402,13 +393,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
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n_hdlc->woke_up = 0;
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spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock, flags);
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- /* get current transmit buffer or get new transmit */
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- /* buffer from list of pending transmit buffers */
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-
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- tbuf = n_hdlc->tbuf;
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- if (!tbuf)
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- tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
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-
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+ tbuf = n_hdlc_buf_get(&n_hdlc->tx_buf_list);
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while (tbuf) {
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if (debuglevel >= DEBUG_LEVEL_INFO)
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printk("%s(%d)sending frame %p, count=%d\n",
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@@ -420,7 +405,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
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/* rollback was possible and has been done */
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if (actual == -ERESTARTSYS) {
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- n_hdlc->tbuf = tbuf;
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+ n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
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break;
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}
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/* if transmit error, throw frame away by */
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@@ -435,10 +420,7 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
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/* free current transmit buffer */
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n_hdlc_buf_put(&n_hdlc->tx_free_buf_list, tbuf);
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-
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- /* this tx buffer is done */
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- n_hdlc->tbuf = NULL;
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-
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+
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/* wait up sleeping writers */
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wake_up_interruptible(&tty->write_wait);
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@@ -448,10 +430,12 @@ static void n_hdlc_send_frames(struct n_hdlc *n_hdlc, struct tty_struct *tty)
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if (debuglevel >= DEBUG_LEVEL_INFO)
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printk("%s(%d)frame %p pending\n",
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__FILE__,__LINE__,tbuf);
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-
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- /* buffer not accepted by driver */
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- /* set this buffer as pending buffer */
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- n_hdlc->tbuf = tbuf;
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+
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+ /*
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+ * the buffer was not accepted by driver,
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+ * return it back into tx queue
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+ */
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+ n_hdlc_buf_return(&n_hdlc->tx_buf_list, tbuf);
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break;
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}
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}
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@@ -749,7 +733,8 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
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int error = 0;
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int count;
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unsigned long flags;
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-
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+ struct n_hdlc_buf *buf = NULL;
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+
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if (debuglevel >= DEBUG_LEVEL_INFO)
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printk("%s(%d)n_hdlc_tty_ioctl() called %d\n",
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__FILE__,__LINE__,cmd);
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@@ -763,8 +748,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
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/* report count of read data available */
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/* in next available frame (if any) */
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spin_lock_irqsave(&n_hdlc->rx_buf_list.spinlock,flags);
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- if (n_hdlc->rx_buf_list.head)
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- count = n_hdlc->rx_buf_list.head->count;
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+ buf = list_first_entry_or_null(&n_hdlc->rx_buf_list.list,
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+ struct n_hdlc_buf, list_item);
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+ if (buf)
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+ count = buf->count;
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else
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count = 0;
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spin_unlock_irqrestore(&n_hdlc->rx_buf_list.spinlock,flags);
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@@ -776,8 +763,10 @@ static int n_hdlc_tty_ioctl(struct tty_struct *tty, struct file *file,
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count = tty_chars_in_buffer(tty);
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/* add size of next output frame in queue */
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spin_lock_irqsave(&n_hdlc->tx_buf_list.spinlock,flags);
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- if (n_hdlc->tx_buf_list.head)
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- count += n_hdlc->tx_buf_list.head->count;
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+ buf = list_first_entry_or_null(&n_hdlc->tx_buf_list.list,
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+ struct n_hdlc_buf, list_item);
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+ if (buf)
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+ count += buf->count;
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spin_unlock_irqrestore(&n_hdlc->tx_buf_list.spinlock,flags);
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error = put_user(count, (int __user *)arg);
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break;
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@@ -825,14 +814,14 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
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poll_wait(filp, &tty->write_wait, wait);
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/* set bits for operations that won't block */
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- if (n_hdlc->rx_buf_list.head)
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+ if (!list_empty(&n_hdlc->rx_buf_list.list))
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mask |= POLLIN | POLLRDNORM; /* readable */
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if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
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mask |= POLLHUP;
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if (tty_hung_up_p(filp))
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mask |= POLLHUP;
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if (!tty_is_writelocked(tty) &&
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- n_hdlc->tx_free_buf_list.head)
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+ !list_empty(&n_hdlc->tx_free_buf_list.list))
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mask |= POLLOUT | POLLWRNORM; /* writable */
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}
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return mask;
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@@ -856,7 +845,12 @@ static struct n_hdlc *n_hdlc_alloc(void)
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spin_lock_init(&n_hdlc->tx_free_buf_list.spinlock);
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spin_lock_init(&n_hdlc->rx_buf_list.spinlock);
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spin_lock_init(&n_hdlc->tx_buf_list.spinlock);
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-
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+
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+ INIT_LIST_HEAD(&n_hdlc->rx_free_buf_list.list);
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+ INIT_LIST_HEAD(&n_hdlc->tx_free_buf_list.list);
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+ INIT_LIST_HEAD(&n_hdlc->rx_buf_list.list);
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+ INIT_LIST_HEAD(&n_hdlc->tx_buf_list.list);
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+
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/* allocate free rx buffer list */
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for(i=0;i<DEFAULT_RX_BUF_COUNT;i++) {
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buf = kmalloc(N_HDLC_BUF_SIZE, GFP_KERNEL);
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@@ -884,53 +878,65 @@ static struct n_hdlc *n_hdlc_alloc(void)
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} /* end of n_hdlc_alloc() */
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/**
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+ * n_hdlc_buf_return - put the HDLC buffer after the head of the specified list
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+ * @buf_list - pointer to the buffer list
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+ * @buf - pointer to the buffer
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+ */
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+static void n_hdlc_buf_return(struct n_hdlc_buf_list *buf_list,
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+ struct n_hdlc_buf *buf)
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+{
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+ unsigned long flags;
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+
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+ spin_lock_irqsave(&buf_list->spinlock, flags);
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+
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+ list_add(&buf->list_item, &buf_list->list);
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+ buf_list->count++;
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+
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+ spin_unlock_irqrestore(&buf_list->spinlock, flags);
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+}
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+
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+/**
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* n_hdlc_buf_put - add specified HDLC buffer to tail of specified list
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- * @list - pointer to buffer list
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+ * @buf_list - pointer to buffer list
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* @buf - pointer to buffer
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*/
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-static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
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+static void n_hdlc_buf_put(struct n_hdlc_buf_list *buf_list,
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struct n_hdlc_buf *buf)
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{
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unsigned long flags;
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- spin_lock_irqsave(&list->spinlock,flags);
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-
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- buf->link=NULL;
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- if (list->tail)
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- list->tail->link = buf;
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- else
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- list->head = buf;
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- list->tail = buf;
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- (list->count)++;
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-
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- spin_unlock_irqrestore(&list->spinlock,flags);
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-
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+
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+ spin_lock_irqsave(&buf_list->spinlock, flags);
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+
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+ list_add_tail(&buf->list_item, &buf_list->list);
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+ buf_list->count++;
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+
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+ spin_unlock_irqrestore(&buf_list->spinlock, flags);
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} /* end of n_hdlc_buf_put() */
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/**
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* n_hdlc_buf_get - remove and return an HDLC buffer from list
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- * @list - pointer to HDLC buffer list
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+ * @buf_list - pointer to HDLC buffer list
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*
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* Remove and return an HDLC buffer from the head of the specified HDLC buffer
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* list.
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* Returns a pointer to HDLC buffer if available, otherwise %NULL.
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*/
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-static struct n_hdlc_buf* n_hdlc_buf_get(struct n_hdlc_buf_list *list)
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+static struct n_hdlc_buf *n_hdlc_buf_get(struct n_hdlc_buf_list *buf_list)
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{
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unsigned long flags;
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struct n_hdlc_buf *buf;
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- spin_lock_irqsave(&list->spinlock,flags);
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-
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- buf = list->head;
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+
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+ spin_lock_irqsave(&buf_list->spinlock, flags);
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+
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+ buf = list_first_entry_or_null(&buf_list->list,
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+ struct n_hdlc_buf, list_item);
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if (buf) {
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- list->head = buf->link;
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- (list->count)--;
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+ list_del(&buf->list_item);
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+ buf_list->count--;
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}
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- if (!list->head)
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- list->tail = NULL;
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-
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- spin_unlock_irqrestore(&list->spinlock,flags);
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+
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+ spin_unlock_irqrestore(&buf_list->spinlock, flags);
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return buf;
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-
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} /* end of n_hdlc_buf_get() */
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static char hdlc_banner[] __initdata =
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--
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2.7.4
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@ -596,6 +596,9 @@ Patch665: netfilter-x_tables-deal-with-bogus-nextoffset-values.patch
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# grabbed from mailing list
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Patch667: v3-Revert-tty-serial-pl011-add-ttyAMA-for-matching-pl011-console.patch
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# CVE-2017-2636 rhbz 1430049
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Patch668: 0001-tty-n_hdlc-get-rid-of-racy-n_hdlc.tbuf.patch
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# END OF PATCH DEFINITIONS
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%endif
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@ -2160,6 +2163,9 @@ fi
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#
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#
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%changelog
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* Tue Mar 07 2017 Laura Abbott <labbott@fedoraproject.org>
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- CVE-2017-2636 Race condition access to n_hdlc.tbuf causes double free in n_hdlc_release (rhbz 1430049)
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* Mon Mar 06 2017 Laura Abbott <labbott@fedoraproject.org> - 4.11.0-0.rc1.git0.1
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- Linux v4.11-rc1
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