treewide: uapi: Replace zero-length arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

This code was transformed with the help of Coccinelle:
(linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch)

@@
identifier S, member, array;
type T1, T2;
@@

struct S {
  ...
  T1 member;
  T2 array[
- 0
  ];
};

-fstrict-flex-arrays=3 is coming and we need to land these changes
to prevent issues like these in the short future:

../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0,
but the source string has length 2 (including NUL byte) [-Wfortify-source]
		strcpy(de3->name, ".");
		^

Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
this breaks anything, we can use a union with a new member name.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Build-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/
Acked-by: Dan Williams <dan.j.williams@intel.com> # For ndctl.h
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 65e13a099b1a..e8191e0c3b56 100644
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -33,7 +33,7 @@ struct xfrm_sec_ctx {
 	__u8	ctx_alg;
 	__u16	ctx_len;
 	__u32	ctx_sid;
-	char	ctx_str[0];
+	char	ctx_str[];
 };
 
 /* Security Context Domains of Interpretation */
@@ -96,27 +96,27 @@ struct xfrm_replay_state_esn {
 	__u32		oseq_hi;
 	__u32		seq_hi;
 	__u32		replay_window;
-	__u32		bmp[0];
+	__u32		bmp[];
 };
 
 struct xfrm_algo {
 	char		alg_name[64];
 	unsigned int	alg_key_len;    /* in bits */
-	char		alg_key[0];
+	char		alg_key[];
 };
 
 struct xfrm_algo_auth {
 	char		alg_name[64];
 	unsigned int	alg_key_len;    /* in bits */
 	unsigned int	alg_trunc_len;  /* in bits */
-	char		alg_key[0];
+	char		alg_key[];
 };
 
 struct xfrm_algo_aead {
 	char		alg_name[64];
 	unsigned int	alg_key_len;	/* in bits */
 	unsigned int	alg_icv_len;	/* in bits */
-	char		alg_key[0];
+	char		alg_key[];
 };
 
 struct xfrm_stats {