From a7ed6c8be4347dc6fd581b1aa130e343fc9202a9 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 20 Jan 2020 17:45:28 -0600 Subject: [PATCH] tty: n_hdlc: Use flexible-array member Old code in the kernel uses 1-byte and 0-byte arrays to indicate the presence of a "variable length array": struct something { int length; u8 data[1]; }; struct something *instance; instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL); instance->length = size; memcpy(instance->data, source, size); There is also 0-byte arrays. Both cases pose confusion for things like sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism to declare variable-length types such as the one above is a flexible array member[2] which need to be the last member of a structure and empty-sized: struct something { int stuff; u8 data[]; }; Also, by making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being unadvertenly introduced[3] to the codebase from now on. [1] https://github.com/KSPP/linux/issues/21 [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- drivers/tty/n_hdlc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index 98361acd3053fd..b5499ca8757ece 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -115,7 +115,7 @@ struct n_hdlc_buf { struct list_head list_item; int count; - char buf[1]; + char buf[]; }; #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)