+ tmpfs-zero-unused-folio-tail-for-long-symlinks.patch added to mm-new branch

+ tmpfs-zero-unused-folio-tail-for-long-symlinks.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: tmpfs: zero unused folio tail for long symlinks
has been added to the -mm mm-new branch.  Its filename is
     tmpfs-zero-unused-folio-tail-for-long-symlinks.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/tmpfs-zero-unused-folio-tail-for-long-symlinks.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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and is updated there most days

------------------------------------------------------
From: Yousef Alhouseen <alhouseenyousef@gmail.com>
Subject: tmpfs: zero unused folio tail for long symlinks
Date: Sun, 28 Jun 2026 02:43:14 +0200

shmem_symlink() marks the entire folio uptodate after copying only the
NUL-terminated link target.  The remainder of the freshly allocated folio
is left uninitialized.

Reclaim may pass the whole folio to a swap compressor.  KMSAN observed
sw842_compress() computing a checksum over the uninitialized tail.  If the
folio is written to a swap device, those bytes can also leave the kernel.

Zero the remainder of the folio before marking it uptodate and dirty.

Link: https://lore.kernel.org/20260628004314.27370-1-alhouseenyousef@gmail.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+bf5586280a66e9ccdfa9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bf5586280a66e9ccdfa9
Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/shmem.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/shmem.c~tmpfs-zero-unused-folio-tail-for-long-symlinks
+++ a/mm/shmem.c
@@ -4057,6 +4057,7 @@ static int shmem_symlink(struct mnt_idma
 			goto out_remove_offset;
 		inode->i_op = &shmem_symlink_inode_operations;
 		memcpy(folio_address(folio), symname, len);
+		folio_zero_range(folio, len, folio_size(folio) - len);
 		folio_mark_uptodate(folio);
 		folio_mark_dirty(folio);
 		folio_unlock(folio);
_

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

tmpfs-zero-unused-folio-tail-for-long-symlinks.patch