Commit ac4149ba authored by Justin Stitt's avatar Justin Stitt Committed by Mike Snitzer
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dm cache metadata: replace deprecated strncpy with strscpy 

`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 (c6b4fcba "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


Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarJustin Stitt <justinstitt@google.com>
Signed-off-by: default avatarMike Snitzer <snitzer@kernel.org>
parent f1445032

drivers/md/dm-cache-metadata.c

+3 −3
Original line number Diff line number Diff line
@@ -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);