tty: hold lock across tty buffer finding and buffer filling

tty_buffer_request_room is well protected, but while after it returns,
 it releases the port->lock. tty->buf.tail might be modified
by either irq handler or other threads. The patch adds more protection
by holding the lock across tty buffer finding and buffer filling.

Signed-off-by: Alek Du <alek.du@intel.com>
Signed-off-by: Xiaobing Tu <xiaobing.tu@intel.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 6c9b7cd6778a9613542d739358f309a38fa56070..91e326ffe7db826054c2607c1ea2688ed047bb81 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -185,25 +185,19 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
        /* Should possibly check if this fails for the largest buffer we
           have queued and recycle that ? */
 }
-
 /**
- *     tty_buffer_request_room         -       grow tty buffer if needed
+ *     __tty_buffer_request_room               -       grow tty buffer if needed
  *     @tty: tty structure
  *     @size: size desired
  *
  *     Make at least size bytes of linear space available for the tty
  *     buffer. If we fail return the size we managed to find.
- *
- *     Locking: Takes tty->buf.lock
+ *      Locking: Caller must hold tty->buf.lock
  */
-int tty_buffer_request_room(struct tty_struct *tty, size_t size)
+static int __tty_buffer_request_room(struct tty_struct *tty, size_t size)
 {
        struct tty_buffer *b, *n;
        int left;
-       unsigned long flags;
-
-       spin_lock_irqsave(&tty->buf.lock, flags);
-
        /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
           remove this conditional if its worth it. This would be invisible
           to the callers */
@@ -225,9 +219,30 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size)
                        size = left;
        }
 
-       spin_unlock_irqrestore(&tty->buf.lock, flags);
        return size;
 }
+
+
+/**
+ *     tty_buffer_request_room         -       grow tty buffer if needed
+ *     @tty: tty structure
+ *     @size: size desired
+ *
+ *     Make at least size bytes of linear space available for the tty
+ *     buffer. If we fail return the size we managed to find.
+ *
+ *     Locking: Takes tty->buf.lock
+ */
+int tty_buffer_request_room(struct tty_struct *tty, size_t size)
+{
+       unsigned long flags;
+       int length;
+
+       spin_lock_irqsave(&tty->buf.lock, flags);
+       length = __tty_buffer_request_room(tty, size);
+       spin_unlock_irqrestore(&tty->buf.lock, flags);
+       return length;
+}
 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 
 /**
@@ -249,14 +264,22 @@ int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
        int copied = 0;
        do {
                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
-               int space = tty_buffer_request_room(tty, goal);
-               struct tty_buffer *tb = tty->buf.tail;
+               int space;
+               unsigned long flags;
+               struct tty_buffer *tb;
+
+               spin_lock_irqsave(&tty->buf.lock, flags);
+               space = __tty_buffer_request_room(tty, goal);
+               tb = tty->buf.tail;
                /* If there is no space then tb may be NULL */
-               if (unlikely(space == 0))
+               if (unlikely(space == 0)) {
+                       spin_unlock_irqrestore(&tty->buf.lock, flags);
                        break;
+               }
                memcpy(tb->char_buf_ptr + tb->used, chars, space);
                memset(tb->flag_buf_ptr + tb->used, flag, space);
                tb->used += space;
+               spin_unlock_irqrestore(&tty->buf.lock, flags);
                copied += space;
                chars += space;
                /* There is a small chance that we need to split the data over
@@ -286,14 +309,22 @@ int tty_insert_flip_string_flags(struct tty_struct *tty,
        int copied = 0;
        do {
                int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
-               int space = tty_buffer_request_room(tty, goal);
-               struct tty_buffer *tb = tty->buf.tail;
+               int space;
+               unsigned long __flags;
+               struct tty_buffer *tb;
+
+               spin_lock_irqsave(&tty->buf.lock, __flags);
+               space = __tty_buffer_request_room(tty, goal);
+               tb = tty->buf.tail;
                /* If there is no space then tb may be NULL */
-               if (unlikely(space == 0))
+               if (unlikely(space == 0)) {
+                       spin_unlock_irqrestore(&tty->buf.lock, __flags);
                        break;
+               }
                memcpy(tb->char_buf_ptr + tb->used, chars, space);
                memcpy(tb->flag_buf_ptr + tb->used, flags, space);
                tb->used += space;
+               spin_unlock_irqrestore(&tty->buf.lock, __flags);
                copied += space;
                chars += space;
                flags += space;
@@ -344,13 +375,20 @@ EXPORT_SYMBOL(tty_schedule_flip);
 int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
                                                                size_t size)
 {
-       int space = tty_buffer_request_room(tty, size);
+       int space;
+       unsigned long flags;
+       struct tty_buffer *tb;
+
+       spin_lock_irqsave(&tty->buf.lock, flags);
+       space = __tty_buffer_request_room(tty, size);
+
+       tb = tty->buf.tail;
        if (likely(space)) {
-               struct tty_buffer *tb = tty->buf.tail;
                *chars = tb->char_buf_ptr + tb->used;
                memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
                tb->used += space;
        }
+       spin_unlock_irqrestore(&tty->buf.lock, flags);
        return space;
 }
 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
@@ -374,13 +412,20 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
 int tty_prepare_flip_string_flags(struct tty_struct *tty,
                        unsigned char **chars, char **flags, size_t size)
 {
-       int space = tty_buffer_request_room(tty, size);
+       int space;
+       unsigned long __flags;
+       struct tty_buffer *tb;
+
+       spin_lock_irqsave(&tty->buf.lock, __flags);
+       space = __tty_buffer_request_room(tty, size);
+
+       tb = tty->buf.tail;
        if (likely(space)) {
-               struct tty_buffer *tb = tty->buf.tail;
                *chars = tb->char_buf_ptr + tb->used;
                *flags = tb->flag_buf_ptr + tb->used;
                tb->used += space;
        }
+       spin_unlock_irqrestore(&tty->buf.lock, __flags);
        return space;
 }
 EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);