treewide: Replace open-coded flex arrays in unions

In support of enabling -Warray-bounds and -Wzero-length-bounds and
correctly handling run-time memcpy() bounds checking, replace all
open-coded flexible arrays (i.e. 0-element arrays) in unions with the
DECLARE_FLEX_ARRAY() helper macro.

This fixes warnings such as:

fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree':
fs/hpfs/anode.c:209:27: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Wzero-length-bounds]
  209 |    anode->btree.u.internal[0].down = cpu_to_le32(a);
      |    ~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from fs/hpfs/hpfs_fn.h:26,
                 from fs/hpfs/anode.c:10:
fs/hpfs/hpfs.h:412:32: note: while referencing 'internal'
  412 |     struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving
      |                                ^~~~~~~~

drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg':
drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds]
  360 |  tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len];
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22,
                 from drivers/net/can/usb/etas_es58x/es58x_fd.c:17:
drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg'
  231 |   u8 raw_msg[0];
      |      ^~~~~~~

Cc: "Gustavo A. R. Silva" <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Ayush Sawal <[email protected]>
Cc: Vinay Kumar Yadav <[email protected]>
Cc: Rohit Maheshwari <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Kalle Valo <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Stanislaw Gruszka <[email protected]>
Cc: Luca Coelho <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: "Martin K. Petersen" <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Cc: Johannes Berg <[email protected]>
Cc: Mordechay Goodstein <[email protected]>
Cc: Lee Jones <[email protected]>
Cc: Wolfgang Grandegger <[email protected]>
Cc: Marc Kleine-Budde <[email protected]>
Cc: Arunachalam Santhanam <[email protected]>
Cc: Vincent Mailhol <[email protected]>
Cc: Mikulas Patocka <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Acked-by: Marc Kleine-Budde <[email protected]> # drivers/net/can/usb/etas_es58x/*
Signed-off-by: Kees Cook <[email protected]>

4 files changed, 16 insertions, 10 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 4a93c12543ee..4298c5e428a3 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -586,8 +586,10 @@ struct bpf_prog {
 	struct bpf_prog_aux	*aux;		/* Auxiliary fields */
 	struct sock_fprog_kern	*orig_prog;	/* Original BPF program */
 	/* Instructions for interpreter */
-	struct sock_filter	insns[0];
-	struct bpf_insn		insnsi[];
+	union {
+		DECLARE_FLEX_ARRAY(struct sock_filter, insns);
+		DECLARE_FLEX_ARRAY(struct bpf_insn, insnsi);
+	};
 };
 
 struct sk_filter {
diff --git a/include/scsi/sas.h b/include/scsi/sas.h
index 4726c1bbec65..64154c1fed02 100644
--- a/include/scsi/sas.h
+++ b/include/scsi/sas.h
@@ -323,8 +323,10 @@ struct ssp_response_iu {
 	__be32 sense_data_len;
 	__be32 response_data_len;
 
-	u8     resp_data[0];
-	u8     sense_data[];
+	union {
+		DECLARE_FLEX_ARRAY(u8, resp_data);
+		DECLARE_FLEX_ARRAY(u8, sense_data);
+	};
 } __attribute__ ((packed));
 
 struct ssp_command_iu {
@@ -554,8 +556,10 @@ struct ssp_response_iu {
 	__be32 sense_data_len;
 	__be32 response_data_len;
 
-	u8     resp_data[0];
-	u8     sense_data[];
+	union {
+		DECLARE_FLEX_ARRAY(u8, resp_data);
+		DECLARE_FLEX_ARRAY(u8, sense_data);
+	};
 } __attribute__ ((packed));
 
 struct ssp_command_iu {
diff --git a/include/uapi/rdma/rdma_user_rxe.h b/include/uapi/rdma/rdma_user_rxe.h
index e283c2220aba..7f44d54bb0ab 100644
--- a/include/uapi/rdma/rdma_user_rxe.h
+++ b/include/uapi/rdma/rdma_user_rxe.h
@@ -141,8 +141,8 @@ struct rxe_dma_info {
 	__u32			sge_offset;
 	__u32			reserved;
 	union {
-		__u8		inline_data[0];
-		struct rxe_sge	sge[0];
+		__DECLARE_FLEX_ARRAY(__u8, inline_data);
+		__DECLARE_FLEX_ARRAY(struct rxe_sge, sge);
 	};
 };
 
diff --git a/include/uapi/sound/asoc.h b/include/uapi/sound/asoc.h
index da61398b1f8f..053949287ce8 100644
--- a/include/uapi/sound/asoc.h
+++ b/include/uapi/sound/asoc.h
@@ -240,8 +240,8 @@ struct snd_soc_tplg_vendor_array {
 struct snd_soc_tplg_private {
 	__le32 size;	/* in bytes of private data */
 	union {
-		char data[0];
-		struct snd_soc_tplg_vendor_array array[0];
+		__DECLARE_FLEX_ARRAY(char, data);
+		__DECLARE_FLEX_ARRAY(struct snd_soc_tplg_vendor_array, array);
 	};
 } __attribute__((packed));