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
Link: https://lkml.kernel.org/r/YxKY6O2hmdwNh8r8@work
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index 638d875..7aebdbf 100644 (file)
--- 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