From 680a93166e80e43e3ff85be06005c5cfa492d852 Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Fri, 28 Feb 2020 07:26:15 -0600 Subject: [PATCH] net: mpls: Replace zero-length array with flexible-array member 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] 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: David S. Miller --- include/net/mpls_iptunnel.h | 2 +- net/mpls/internal.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/net/mpls_iptunnel.h b/include/net/mpls_iptunnel.h index 6b4759eae158..9deb3a3735da 100644 --- a/include/net/mpls_iptunnel.h +++ b/include/net/mpls_iptunnel.h @@ -11,7 +11,7 @@ struct mpls_iptunnel_encap { u8 ttl_propagate; u8 default_ttl; u8 reserved1; - u32 label[0]; + u32 label[]; }; static inline struct mpls_iptunnel_encap *mpls_lwtunnel_encap(struct lwtunnel_state *lwtstate) diff --git a/net/mpls/internal.h b/net/mpls/internal.h index 768a302879b4..0e9aa94adc07 100644 --- a/net/mpls/internal.h +++ b/net/mpls/internal.h @@ -98,7 +98,7 @@ struct mpls_nh { /* next hop label forwarding entry */ u8 nh_via_table; u8 nh_reserved1; - u32 nh_label[0]; + u32 nh_label[]; }; /* offset of via from beginning of mpls_nh */ @@ -154,7 +154,7 @@ struct mpls_route { /* next hop label forwarding entry */ u8 rt_nh_size; u8 rt_via_offset; u8 rt_reserved1; - struct mpls_nh rt_nh[0]; + struct mpls_nh rt_nh[]; }; #define for_nexthops(rt) { \ -- 2.11.0