pstore/ram: 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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20200309202327.GA8813@embeddedor
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Gustavo A. R. Silva 2020-03-09 15:23:27 -05:00 committed by Kees Cook
parent 6c871b7314
commit 8128d3aac0
1 changed files with 1 additions and 1 deletions

View File

@ -34,7 +34,7 @@ struct persistent_ram_buffer {
uint32_t sig;
atomic_t start;
atomic_t size;
uint8_t data[0];
uint8_t data[];
};
#define PERSISTENT_RAM_SIG (0x43474244) /* DBGC */