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

fujunjie
2026-04-26T11:08:31Z

process_madvise() validates the advice while walking the imported iovec.
If the iovec has zero total length, vector_madvise() never enters the
loop and returns 0 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.

Reject invalid advice before walking the vector. Valid zero-length
requests remain no-ops 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 valid zero-length request still
succeeds.

Fixes: 021781b01275 ("mm/madvise: unrestrict process_madvise() for current process")
Signed-off-by: fujunjie <fujunjie1@qq.com>
---
Testing:
- Built bzImage.
- Built tools/testing/selftests/mm/process_madv.
- Ran tools/testing/selftests/mm/process_madv in QEMU:
# PASSED: 7 / 7 tests passed.

mm/madvise.c | 3 +++
tools/testing/selftests/mm/process_madv.c | 29 +++++++++++++++++++++++
2 files changed, 32 insertions(+)

diff --git a/mm/madvise.c b/mm/madvise.c
index 69708e953cf56..83fe9e651a907 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -2046,6 +2046,9 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,

total_len = iov_iter_count(iter);

+ if (!madvise_behavior_valid(behavior))
+ return -EINVAL;
+
ret = madvise_lock(&madv_behavior);
if (ret)
return ret;
diff --git a/tools/testing/selftests/mm/process_madv.c b/tools/testing/selftests/mm/process_madv.c
index cd4610baf5d7d..9a7e2788fcc50 100644
--- a/tools/testing/selftests/mm/process_madv.c
+++ b/tools/testing/selftests/mm/process_madv.c
@@ -309,6 +309,35 @@ TEST_F(process_madvise, invalid_vlen)
ASSERT_EQ(munmap(map, pagesize), 0);
}

+/*
+ * Test that invalid advice is rejected even when the iovec has zero total
+ * length. A zero-length advice is a no-op for valid advice, but invalid
+ * advice should still fail with EINVAL.
+ */
+TEST_F(process_madvise, invalid_advice_zero_length)
+{
+ struct iovec vec = {
+ .iov_base = NULL,
+ .iov_len = 0,
+ };
+ int pidfd = self->pidfd;
+ ssize_t ret;
+
+ errno = 0;
+ ret = sys_process_madvise(pidfd, &vec, 1, -1, 0);
+ ASSERT_EQ(ret, -1);
+ ASSERT_EQ(errno, EINVAL);
+
+ errno = 0;
+ ret = sys_process_madvise(pidfd, &vec, 1, MADV_DONTNEED, 0);
+ ASSERT_EQ(ret, 0);
+
+ errno = 0;
+ ret = sys_process_madvise(pidfd, NULL, 0, -1, 0);
+ ASSERT_EQ(ret, -1);
+ ASSERT_EQ(errno, EINVAL);
+}
+
/*
* Test process_madvise() with an invalid flag value. Currently, only a flag
* value of 0 is supported. This test is reserved for the future, e.g., if

base-commit: 1b55f8358e35a67bf3969339ea7b86988af92f66
--
2.34.1