+ selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test.patch added to mm-unstable branch

+ selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: fix unchecked ftruncate return value in soft-dirty test
has been added to the -mm mm-unstable branch.  Its filename is
     selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Anshuman <anshumantewari123@gmail.com>
Subject: selftests/mm: fix unchecked ftruncate return value in soft-dirty test
Date: Tue, 18 Aug 2026 19:02:06 +0530

test_mprotect() calls ftruncate() to resize the backing file before
mmap()'ing it, but never checks the return value.  If ftruncate() fails,
the file may remain shorter than the requested mapping size.  The
subsequent mmap() with MAP_SHARED can still succeed in this case, but the
very next line writes directly into the mapped memory (*map = 1), which
can trigger SIGBUS if the mapping extends beyond the actual file size.

Check the return value and fail cleanly with ksft_exit_fail_msg() if
ftruncate() fails, matching the error-handling style already used for the
mmap() call immediately below it.

Link: https://lore.kernel.org/20260818133206.39503-1-anshumantewari123@gmail.com
Signed-off-by: Anshuman <anshumantewari123@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/soft-dirty.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/tools/testing/selftests/mm/soft-dirty.c~selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test
+++ a/tools/testing/selftests/mm/soft-dirty.c
@@ -152,7 +152,8 @@ static void test_mprotect(int pagemap_fd
 			return;
 		}
 		unlink(fname);
-		ftruncate(test_fd, pagesize);
+		if (ftruncate(test_fd, pagesize) != 0)
+			ksft_exit_fail_msg("ftruncate failed\n");
 		map = mmap(NULL, pagesize, PROT_READ|PROT_WRITE,
 			   MAP_SHARED, test_fd, 0);
 		if (map == MAP_FAILED)
_

Patches currently in -mm which might be from anshumantewari123@gmail.com are

selftests-mm-fix-unchecked-ftruncate-return-value-in-soft-dirty-test.patch