commit 6a7de1bf218d75f27f68d6a3f5ae1eb7332b941e upstream.

page_folio() calls page_fixed_fake_head() which will misidentify this page
as being a fake head and load off the end of 'precise'.  We may have a
pointer to a fake head, but that's OK because it contains the right
information for dump_page().

gcc-15 is smart enough to catch this with -Warray-bounds:

In function 'page_fixed_fake_head',
    inlined from '_compound_head' at ../include/linux/page-flags.h:251:24,
    inlined from '__dump_page' at ../mm/debug.c:123:11:
../include/asm-generic/rwonce.h:44:26: warning: array subscript 9 is outside
+array bounds of 'struct page[1]' [-Warray-bounds=]

Link: https://lkml.kernel.org/r/20241125201721.2963278-2-willy@infradead.org


Fixes: fae7d834 ("mm: add __dump_folio()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: Kees Cook <kees@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>