unimore/kernel-hacking-2024-linux-steffo
unimore/kernel-hacking-2024-linux-steffo
1
Fork 0
Code Pull requests 5 Wiki Activity

net: dccp: Replace zero-length array with flexible-array member

Browse source 
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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gustavo A. R. Silva 2020-02-28 07:33:37 -06:00 committed by David S. Miller
parent af71b090c8
commit 8402a31dd8
2 changed files with 2 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
include/linux/dccp.h
View file

@ -198,7 +198,7 @@ enum dccp_role {
struct dccp_service_list { struct dccp_service_list {
__u32 dccpsl_nr; __u32 dccpsl_nr;
__be32 dccpsl_list[0]; __be32 dccpsl_list[];
}; };
#define DCCP_SERVICE_INVALID_VALUE htonl((__u32)-1) #define DCCP_SERVICE_INVALID_VALUE htonl((__u32)-1)

2
net/dccp/ccid.h
View file

@ -95,7 +95,7 @@ void ccid_cleanup_builtins(void);
struct ccid { struct ccid {
struct ccid_operations *ccid_ops; struct ccid_operations *ccid_ops;
char ccid_priv[0]; char ccid_priv[];
}; };
static inline void *ccid_priv(const struct ccid *ccid) static inline void *ccid_priv(const struct ccid *ccid)