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Message-ID: <20230925-strncpy-drivers-md-dm-cache-metadata-c-v1-1-4b75c7db0cfe@google.com>
Date: Mon, 25 Sep 2023 06:13:12 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Alasdair Kergon <agk@...hat.com>,
Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com
Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] 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 (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@...r.kernel.org
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Note: build-tested only.
---
drivers/md/dm-cache-metadata.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
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);
---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230925-strncpy-drivers-md-dm-cache-metadata-c-f708096d5d22
Best regards,
--
Justin Stitt <justinstitt@...gle.com>
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