linux-hardening - [PATCH][next] ocfs2: Replace zero-length arrays with DECLARE_FLEX

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Date:   Sat, 3 Sep 2022 00:59:36 +0100
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] ocfs2: Replace zero-length arrays with
 DECLARE_FLEX_ARRAY() helper

Zero-length arrays are deprecated and we are moving towards adopting
C99 flexible-array members, instead. So, replace zero-length array
declarations in a couple of structures and unions with the new
DECLARE_FLEX_ARRAY() helper macro.

This helper allows for a flexible-array member in a union and as
only member in a structure.

Also, this addresses multiple warnings reported when building with
Clang-15 and -Wzero-length-array.

Lastly, this will also help memcpy (in a coming hardening update)
execute proper bounds-checking on variable length object i_symlink
at fs/ocfs2/namei.c:1973:

fs/ocfs2/namei.c:
1973                 memcpy((char *) fe->id2.i_symlink, symname, l);

Link: https://github.com/KSPP/linux/issues/21
Link: https://github.com/KSPP/linux/issues/193
Link: https://github.com/KSPP/linux/issues/197
Link: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 fs/ocfs2/ocfs2_fs.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index 638d875eccc7..7aebdbf5cc0a 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -527,7 +527,7 @@ struct ocfs2_extent_block
  * value -1 (0xFFFF) is OCFS2_INVALID_SLOT.  This marks a slot empty.
  */
 struct ocfs2_slot_map {
-/*00*/	__le16 sm_slots[0];
+/*00*/	DECLARE_FLEX_ARRAY(__le16, sm_slots);
 /*
  * Actual on-disk size is one block.  OCFS2_MAX_SLOTS is 255,
  * 255 * sizeof(__le16) == 512B, within the 512B block minimum blocksize.
@@ -548,7 +548,7 @@ struct ocfs2_extended_slot {
  * i_size.
  */
 struct ocfs2_slot_map_extended {
-/*00*/	struct ocfs2_extended_slot se_slots[0];
+/*00*/	DECLARE_FLEX_ARRAY(struct ocfs2_extended_slot, se_slots);
 /*
  * Actual size is i_size of the slot_map system file.  It should
  * match s_max_slots * sizeof(struct ocfs2_extended_slot)
@@ -727,7 +727,7 @@ struct ocfs2_dinode {
 		struct ocfs2_extent_list	i_list;
 		struct ocfs2_truncate_log	i_dealloc;
 		struct ocfs2_inline_data	i_data;
-		__u8               		i_symlink[0];
+		DECLARE_FLEX_ARRAY(__u8,	i_symlink);
 	} id2;
 /* Actual on-disk size is one block */
 };
@@ -892,7 +892,7 @@ struct ocfs2_group_desc
 /*30*/	struct ocfs2_block_check bg_check;	/* Error checking */
 	__le64   bg_reserved2;
 /*40*/	union {
-		__u8    bg_bitmap[0];
+		DECLARE_FLEX_ARRAY(__u8, bg_bitmap);
 		struct {
 			/*
 			 * Block groups may be discontiguous when
-- 
2.34.1