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 nfs4_ff_layout_segment.

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

Cc: Trond Myklebust <trond.mykleb...@hammerspace.com>
Cc: Anna Schumaker <a...@kernel.org>
Cc: linux-...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 fs/nfs/flexfilelayout/flexfilelayout.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/flexfilelayout/flexfilelayout.h 
b/fs/nfs/flexfilelayout/flexfilelayout.h
index 354a031c69b1..f84b3fb0dddd 100644
--- a/fs/nfs/flexfilelayout/flexfilelayout.h
+++ b/fs/nfs/flexfilelayout/flexfilelayout.h
@@ -99,7 +99,7 @@ struct nfs4_ff_layout_segment {
        u64                             stripe_unit;
        u32                             flags;
        u32                             mirror_array_cnt;
-       struct nfs4_ff_layout_mirror    *mirror_array[];
+       struct nfs4_ff_layout_mirror    *mirror_array[] 
__counted_by(mirror_array_cnt);
 };
 
 struct nfs4_flexfile_layout {
-- 
2.34.1

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