From 631512f868a4a49a48bda753752d085621c68112 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Wed, 13 May 2020 12:15:56 -0500 Subject: [PATCH] Bluetooth: L2CAP: Replace zero-length array with flexible-array The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; 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 inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva Signed-off-by: Marcel Holtmann --- include/net/bluetooth/l2cap.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index dada14d0622c..8f1e6a7a2df8 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -499,7 +499,7 @@ struct l2cap_ecred_conn_req { __le16 mtu; __le16 mps; __le16 credits; - __le16 scid[0]; + __le16 scid[]; } __packed; struct l2cap_ecred_conn_rsp { @@ -507,13 +507,13 @@ struct l2cap_ecred_conn_rsp { __le16 mps; __le16 credits; __le16 result; - __le16 dcid[0]; + __le16 dcid[]; }; struct l2cap_ecred_reconf_req { __le16 mtu; __le16 mps; - __le16 scid[0]; + __le16 scid[]; } __packed; #define L2CAP_RECONF_SUCCESS 0x0000