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    Subject[PATCH AUTOSEL for 4.9 140/293] ext4: require key for truncate(2) of encrypted file
    Date
    From: Eric Biggers <ebiggers@google.com>

    [ Upstream commit 63136858aecbe86dbd3c3289a3f46ba1b5f92239 ]

    Currently, filesystems allow truncate(2) on an encrypted file without
    the encryption key. However, it's impossible to correctly handle the
    case where the size being truncated to is not a multiple of the
    filesystem block size, because that would require decrypting the final
    block, zeroing the part beyond i_size, then encrypting the block.

    As other modifications to encrypted file contents are prohibited without
    the key, just prohibit truncate(2) as well, making it fail with ENOKEY.

    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    fs/ext4/inode.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
    index 5cccec68a0a5..58d57c56ec62 100644
    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -5166,6 +5166,14 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
    loff_t oldsize = inode->i_size;
    int shrink = (attr->ia_size <= inode->i_size);

    + if (ext4_encrypted_inode(inode)) {
    + error = fscrypt_get_encryption_info(inode);
    + if (error)
    + return error;
    + if (!fscrypt_has_encryption_key(inode))
    + return -ENOKEY;
    + }
    +
    if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
    struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);

    --
    2.15.1
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