Ocfs2 devel - Sep 2022 - [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 at kernel.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

On Sat, Sep 03, 2022 at 12:59:36AM +0100, Gustavo A. R. Silva
wrote:
> 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 at kernel.org>
Reviewed-by: Kees Cook <keescook at chromium.org>

-- 
Kees Cook

On 9/3/22 7:59 AM, Gustavo A. R. Silva wrote:
> 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 at kernel.org>
Looks good.
Reviewed-by: Joseph Qi <joseph.qi at linux.alibaba.com>