Messages in this thread Patch in this message | | | Date | Mon, 17 Feb 2020 14:01:11 -0600 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH][next] bpf, sockmap: Replace zero-length array with flexible-array member |
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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 <gustavo@embeddedor.com> --- net/core/sock_map.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/sock_map.c b/net/core/sock_map.c index 085cef5857bb..3a7a96ab088a 100644 --- a/net/core/sock_map.c +++ b/net/core/sock_map.c @@ -518,7 +518,7 @@ struct bpf_htab_elem { u32 hash; struct sock *sk; struct hlist_node node; - u8 key[0]; + u8 key[]; }; struct bpf_htab_bucket { -- 2.25.0
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