From:   "Matthew Wilcox (Oracle)" <willy@infradead.org>
To:     linux-fsdevel@vger.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-afs@lists.infradead.org, linux-btrfs@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-mm@kvack.org,
        Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org,
        fstests@vger.kernel.org
Subject: [PATCH 3/5] tmpfs: Zero bytes after 'oldsize' if we're expanding the file
Date:   Thu,  2 Feb 2023 20:44:25 +0000
Message-Id: <20230202204428.3267832-4-willy@infradead.org>
In-Reply-To: <20230202204428.3267832-1-willy@infradead.org>
References: <20230202204428.3267832-1-willy@infradead.org>
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POSIX requires that "If the file size is increased, the extended area
shall appear as if it were zero-filled".  It is possible to use mmap to
write past EOF and that data will become visible instead of zeroes.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/shmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 0005ab2c29af..2c8e8b417b00 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1124,6 +1124,8 @@ static int shmem_setattr(struct user_namespace *mnt_userns,
 			if (oldsize > holebegin)
 				unmap_mapping_range(inode->i_mapping,
 							holebegin, 0, 1);
+		} else {
+			shmem_truncate_range(inode, oldsize, newsize);
 		}
 	}
 
-- 
2.35.1