BUG/MEDIUM: channel: fix possible integer overflow on reserved size computation
The buffer_max_len() function is subject to an integer overflow in this
calculus :
int ret = global.tune.maxrewrite - chn->to_forward - chn->buf->o;
- chn->to_forward may be up to 2^31 - 1
- chn->buf->o may be up to chn->buf->size
- global.tune.maxrewrite is by definition smaller than chn->buf->size
Thus here we can subtract (2^31 + buf->o) (highly negative) from something
slightly positive, and result in ret being larger than expected.
Fortunately in 1.5 and 1.6, this is only used by bi_avail() which itself
is used by applets which do not set high values for to_forward so this
problem does not happen there. However in 1.4 the equivalent computation
was used to limit the size of a read and can result in a read overflow
when combined with the nasty http-send-name-header feature.
This fix must be backported to 1.5 and 1.4.
diff --git a/include/proto/channel.h b/include/proto/channel.h
index e38e375..3ec9218 100644
--- a/include/proto/channel.h
+++ b/include/proto/channel.h
@@ -258,17 +258,22 @@
* buffer, which ensures that once all pending data are forwarded, the
* buffer still has global.tune.maxrewrite bytes free. The result is
* between 0 and global.tune.maxrewrite, which is itself smaller than
- * any chn->size.
+ * any chn->size. Special care is taken to avoid any possible integer
+ * overflow in the operations.
*/
static inline int buffer_reserved(const struct channel *chn)
{
- int ret = global.tune.maxrewrite - chn->to_forward - chn->buf->o;
+ unsigned int reserved = global.tune.maxrewrite;
+
+ if (chn->to_forward == CHN_INFINITE_FORWARD ||
+ chn->to_forward >= reserved ||
+ chn->buf->o >= reserved ||
+ chn->to_forward + chn->buf->o >= reserved)
+ reserved = 0;
+ else
+ reserved -= chn->to_forward + chn->buf->o;
- if (chn->to_forward == CHN_INFINITE_FORWARD)
- return 0;
- if (ret <= 0)
- return 0;
- return ret;
+ return reserved;
}
/* Return the max number of bytes the buffer can contain so that once all the