afs: Annotate struct afs_permits 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 afs_permits.

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

Cc: David Howells <dhowells@redhat.com>
Cc: Marc Dionne <marc.dionne@auristor.com>
Cc: linux-afs@lists.infradead.org
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230915201456.never.529-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index da73b97..813efd3 100644 (file)
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -705,7 +705,7 @@ struct afs_permits {
        refcount_t              usage;
        unsigned short          nr_permits;     /* Number of records */
        bool                    invalidated;    /* Invalidated due to key change */
-       struct afs_permit       permits[];      /* List of permits sorted by key pointer */
+       struct afs_permit       permits[] __counted_by(nr_permits);     /* List of permits sorted by key pointer */
 };
 
 /*