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b=H4sIAPckEWUC/x3NwQrCMAyA4VcZORuoHVPnq4iHkGQuh9aRljEZe /cVj9/l/3co6qYFnt0OrqsV++aG66UDnil/FE2aIYbYhzEOWKpnXn4obqt6wSQoCZl4VkxaSag SMk738AjjTQaJEVpscZ1s+49e7+M4AWGjYUx4AAAA X-Developer-Key: i=justinstitt@google.com; a=ed25519; pk=tC3hNkJQTpNX/gLKxTNQKDmiQl6QjBNCGKJINqAdJsE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1695622392; l=3897; i=justinstitt@google.com; s=20230717; h=from:subject:message-id; bh=L9/fdUPf3xhTtPuNBdXSMdi4yA/i8QBeE3Azuo4x1V4=; b=s7K9oW+wn0ijUhrySteAlkbaAM8X5C4rkp3jki9seVEy0xY+hLk287rA8MGz9tW8TbMwZetUm /4fAXWdPvzQAg+tYrQ200y/X9gvS7KkXrTc3YzrqfbEeKZlVPYYe+Tj X-Mailer: b4 0.12.3 Message-ID: <20230925-strncpy-drivers-md-dm-cache-metadata-c-v1-1-4b75c7db0cfe@google.com> Subject: [PATCH] dm cache metadata: replace deprecated strncpy with strscpy From: Justin Stitt To: Alasdair Kergon , Mike Snitzer , dm-devel@redhat.com Cc: linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, Justin Stitt X-Spam-Status: No, score=-9.6 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Sun, 24 Sep 2023 23:13:31 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1778015503639001097 X-GMAIL-MSGID: 1778015503639001097 `strncpy` is deprecated for use on NUL-terminated destination strings [1] and as such we should prefer more robust and less ambiguous string interfaces. It seems `cmd->policy_name` is intended to be NUL-terminated based on a now changed line of code from Commit (c6b4fcbad044e6ff "dm: add cache target"): | if (strcmp(cmd->policy_name, policy_name)) { // ... However, now a length-bounded strncmp is used: | if (strncmp(cmd->policy_name, policy_name, sizeof(cmd->policy_name))) ... which means NUL-terminated may not strictly be required. However, I believe the intent of the code is clear and we should maintain NUL-termination of policy_names. Moreover, __begin_transaction_flags() zero-allocates `cmd` before calling read_superblock_fields(): | cmd = kzalloc(sizeof(*cmd), GFP_KERNEL); Also, `disk_super->policy_name` is zero-initialized | memset(disk_super->policy_name, 0, sizeof(disk_super->policy_name)); ... therefore any NUL-padding is redundant. Considering the above, a suitable replacement is `strscpy` [2] due to the fact that it guarantees NUL-termination on the destination buffer without unnecessarily NUL-padding. Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1] Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@vger.kernel.org Signed-off-by: Justin Stitt Reviewed-by: Kees Cook --- Note: build-tested only. --- drivers/md/dm-cache-metadata.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- base-commit: 6465e260f48790807eef06b583b38ca9789b6072 change-id: 20230925-strncpy-drivers-md-dm-cache-metadata-c-f708096d5d22 Best regards, -- Justin Stitt diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c index acffed750e3e..5a18b80d3666 100644 --- a/drivers/md/dm-cache-metadata.c +++ b/drivers/md/dm-cache-metadata.c @@ -597,7 +597,7 @@ static void read_superblock_fields(struct dm_cache_metadata *cmd, cmd->discard_nr_blocks = to_dblock(le64_to_cpu(disk_super->discard_nr_blocks)); cmd->data_block_size = le32_to_cpu(disk_super->data_block_size); cmd->cache_blocks = to_cblock(le32_to_cpu(disk_super->cache_blocks)); - strncpy(cmd->policy_name, disk_super->policy_name, sizeof(cmd->policy_name)); + strscpy(cmd->policy_name, disk_super->policy_name, sizeof(cmd->policy_name)); cmd->policy_version[0] = le32_to_cpu(disk_super->policy_version[0]); cmd->policy_version[1] = le32_to_cpu(disk_super->policy_version[1]); cmd->policy_version[2] = le32_to_cpu(disk_super->policy_version[2]); @@ -707,7 +707,7 @@ static int __commit_transaction(struct dm_cache_metadata *cmd, disk_super->discard_block_size = cpu_to_le64(cmd->discard_block_size); disk_super->discard_nr_blocks = cpu_to_le64(from_dblock(cmd->discard_nr_blocks)); disk_super->cache_blocks = cpu_to_le32(from_cblock(cmd->cache_blocks)); - strncpy(disk_super->policy_name, cmd->policy_name, sizeof(disk_super->policy_name)); + strscpy(disk_super->policy_name, cmd->policy_name, sizeof(disk_super->policy_name)); disk_super->policy_version[0] = cpu_to_le32(cmd->policy_version[0]); disk_super->policy_version[1] = cpu_to_le32(cmd->policy_version[1]); disk_super->policy_version[2] = cpu_to_le32(cmd->policy_version[2]); @@ -1726,7 +1726,7 @@ static int write_hints(struct dm_cache_metadata *cmd, struct dm_cache_policy *po (strlen(policy_name) > sizeof(cmd->policy_name) - 1)) return -EINVAL; - strncpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name)); + strscpy(cmd->policy_name, policy_name, sizeof(cmd->policy_name)); memcpy(cmd->policy_version, policy_version, sizeof(cmd->policy_version)); hint_size = dm_cache_policy_get_hint_size(policy);