selftests/prctl: fix non-anonymous VMA mapping in set-anon-vma-name test

The test creates a non-anonymous VMA (ptr_not_anon) via mmap() with
MAP_PRIVATE but without MAP_ANONYMOUS, using fd=0 (stdin) as the file
descriptor.  This always fails because fd=0 is not a regular file, and the
failure was hidden because ASSERT_NE() incorrectly checked for NULL
instead of MAP_FAILED.

Fix by using mkstemp() + ftruncate() to create a real temporary file, then
mapping it with MAP_PRIVATE to obtain a genuine file-backed VMA.  Also fix
the mmap() error checks to use MAP_FAILED instead of NULL, and pass fd=-1
for the anonymous mapping for clarity.  The temp file is unlinked
immediately so it does not persist on disk.

Link: https://lore.kernel.org/20260803103046.14324-1-hongfu.li@linux.dev
Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions