linux-kernel - [PATCH] NFS/flexfiles: Annotate struct nfs4_ff_layout_segment with __counted

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Date:   Fri, 15 Sep 2023 13:14:39 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Trond Myklebust <trond.myklebust@...merspace.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: [PATCH] NFS/flexfiles: Annotate struct nfs4_ff_layout_segment with __counted_by

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.myklebust@...merspace.com>
Cc: Anna Schumaker <anna@...nel.org>
Cc: linux-nfs@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.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