[PATCH] Fix tty layer DoS and comment relevant code
Unlike the other tty comment patch this one has code changes. Specifically
it limits the queue size for a tty to 64K characters (128Kbytes) worst case
even if the tty is ignoring tty->throttle. This is because certain drivers
don't honour the throttle value correctly, although it is a useful
safeguard anyway.
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 2cef982..bb0d919 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -275,6 +275,17 @@
* Locking: none
*/
+
+/**
+ * tty_buffer_free_all - free buffers used by a tty
+ * @tty: tty to free from
+ *
+ * Remove all the buffers pending on a tty whether queued with data
+ * or in the free ring. Must be called when the tty is no longer in use
+ *
+ * Locking: none
+ */
+
static void tty_buffer_free_all(struct tty_struct *tty)
{
struct tty_buffer *thead;
@@ -287,19 +298,47 @@
kfree(thead);
}
tty->buf.tail = NULL;
+ tty->buf.memory_used = 0;
}
+/**
+ * tty_buffer_init - prepare a tty buffer structure
+ * @tty: tty to initialise
+ *
+ * Set up the initial state of the buffer management for a tty device.
+ * Must be called before the other tty buffer functions are used.
+ *
+ * Locking: none
+ */
+
static void tty_buffer_init(struct tty_struct *tty)
{
spin_lock_init(&tty->buf.lock);
tty->buf.head = NULL;
tty->buf.tail = NULL;
tty->buf.free = NULL;
+ tty->buf.memory_used = 0;
}
-static struct tty_buffer *tty_buffer_alloc(size_t size)
+/**
+ * tty_buffer_alloc - allocate a tty buffer
+ * @tty: tty device
+ * @size: desired size (characters)
+ *
+ * Allocate a new tty buffer to hold the desired number of characters.
+ * Return NULL if out of memory or the allocation would exceed the
+ * per device queue
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
+static struct tty_buffer *tty_buffer_alloc(struct tty_struct *tty, size_t size)
{
- struct tty_buffer *p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
+ struct tty_buffer *p;
+
+ if (tty->buf.memory_used + size > 65536)
+ return NULL;
+ p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
if(p == NULL)
return NULL;
p->used = 0;
@@ -309,17 +348,27 @@
p->read = 0;
p->char_buf_ptr = (char *)(p->data);
p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
-/* printk("Flip create %p\n", p); */
+ tty->buf.memory_used += size;
return p;
}
-/* Must be called with the tty_read lock held. This needs to acquire strategy
- code to decide if we should kfree or relink a given expired buffer */
+/**
+ * tty_buffer_free - free a tty buffer
+ * @tty: tty owning the buffer
+ * @b: the buffer to free
+ *
+ * Free a tty buffer, or add it to the free list according to our
+ * internal strategy
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
static void tty_buffer_free(struct tty_struct *tty, struct tty_buffer *b)
{
/* Dumb strategy for now - should keep some stats */
-/* printk("Flip dispose %p\n", b); */
+ tty->buf.memory_used -= b->size;
+ WARN_ON(tty->buf.memory_used < 0);
+
if(b->size >= 512)
kfree(b);
else {
@@ -328,6 +377,18 @@
}
}
+/**
+ * tty_buffer_find - find a free tty buffer
+ * @tty: tty owning the buffer
+ * @size: characters wanted
+ *
+ * Locate an existing suitable tty buffer or if we are lacking one then
+ * allocate a new one. We round our buffers off in 256 character chunks
+ * to get better allocation behaviour.
+ *
+ * Locking: Caller must hold tty->buf.lock
+ */
+
static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
{
struct tty_buffer **tbh = &tty->buf.free;
@@ -339,20 +400,28 @@
t->used = 0;
t->commit = 0;
t->read = 0;
- /* DEBUG ONLY */
-/* memset(t->data, '*', size); */
-/* printk("Flip recycle %p\n", t); */
+ tty->buf.memory_used += t->size;
return t;
}
tbh = &((*tbh)->next);
}
/* Round the buffer size out */
size = (size + 0xFF) & ~ 0xFF;
- return tty_buffer_alloc(size);
+ return tty_buffer_alloc(tty, 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: 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)
{
struct tty_buffer *b, *n;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index e421d5e..04827ca 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -59,6 +59,7 @@
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */
struct tty_buffer *free; /* Free queue head */
+ int memory_used; /* Buffer space used excluding free queue */
};
/*
* The pty uses char_buf and flag_buf as a contiguous buffer
