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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. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+bf5586280a66e9ccdfa9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=bf5586280a66e9ccdfa9 Cc: stable@vger.kernel.org Signed-off-by: Yousef Alhouseen --- mm/shmem.c | 1 + 1 file changed, 1 insertion(+) diff --git a/mm/shmem.c b/mm/shmem.c index b51f83c970bb..b06c1ae2f50c 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -4057,6 +4057,7 @@ static int shmem_symlink(struct mnt_idmap *idmap, struct inode *dir, 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); -- 2.54.0