mm/madvise: reject invalid process_madvise() advice for zero-length vectors

process_madvise() used to validate the advice while walking each imported
iovec.  If the vector has zero total length, vector_madvise() does not
enter the loop and can return success without checking whether the advice
value is valid.

For a local mm, such as process_madvise(PIDFD_SELF, ...), the remote-only
process_madvise_remote_valid() check is skipped.  As a result, an invalid
advice can be reported as success when the vector has zero total length. 
This differs from madvise(), which rejects an invalid advice before
returning success for a zero-length range.

Validate the generic madvise behavior at the syscall-facing entry points
before any vector walk.  In process_madvise(), do this before the
remote-only advice restriction so unsupported advice is rejected with the
same priority for local and remote mm.

Use an errno-returning helper for address/length validation, and handle
zero-length ranges explicitly at the call sites.  Requests with valid
advice and zero total length remain a noop and continue to return 0.  Add
a selftest that covers invalid advice with a zero-length iovec and an
empty vector, while also checking that a request with valid advice and
zero length still succeeds.

Link: https://lore.kernel.org/tencent_C3AEB0E769C5F4F9370F9411B69B7F8B2907@qq.com
Fixes: 021781b01275 ("mm/madvise: unrestrict process_madvise() for current process")
Signed-off-by: fujunjie <fujunjie1@qq.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions