Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct ocfs2_slot_info.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Mark Fasheh <m...@fasheh.com>
Cc: Joel Becker <jl...@evilplan.org>
Cc: Joseph Qi <joseph...@linux.alibaba.com>
Cc: ocfs2-de...@lists.linux.dev
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 fs/ocfs2/slot_map.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ocfs2/slot_map.c b/fs/ocfs2/slot_map.c
index da7718cef735..e544c704b583 100644
--- a/fs/ocfs2/slot_map.c
+++ b/fs/ocfs2/slot_map.c
@@ -37,7 +37,7 @@ struct ocfs2_slot_info {
        unsigned int si_blocks;
        struct buffer_head **si_bh;
        unsigned int si_num_slots;
-       struct ocfs2_slot si_slots[];
+       struct ocfs2_slot si_slots[] __counted_by(si_num_slots);
 };
 
 
-- 
2.34.1

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