[PATCH v2] qed: replace uses of strncpy

[PATCH v2] qed: replace uses of strncpy

[Justin Stitt]

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

This patch eliminates three uses of strncpy():

Firstly, `dest` is expected to be NUL-terminated which is evident by the
manual setting of a NUL-byte at size - 1. For this use specifically,
strscpy() is a viable replacement due to the fact that it guarantees
NUL-termination on the destination buffer.

The next two cases should simply be memcpy() as the size of the src
string is always 3 and the destination string just wants the first 3
bytes changed.

To be clear, there are no buffer overread bugs in the current code as
the sizes and offsets are carefully managed such that buffers are
NUL-terminated. However, with these changes, the code is now more robust
and less ambiguous (and hopefully easier to read).

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
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- prefer memcpy to snprintf (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20231011-strncpy-drivers-net-ethernet-qlogic-qed-qed_debug-c-v1-1-60c9ca2d54a2@google.com
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/ethernet/qlogic/qed/qed_debug.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/qed/qed_debug.c b/drivers/net/ethernet/qlogic/qed/qed_debug.c
index cdcead614e9f..f67be4b8ad43 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_debug.c
+++ b/drivers/net/ethernet/qlogic/qed/qed_debug.c
@@ -3204,8 +3204,8 @@ static u32 qed_grc_dump_big_ram(struct qed_hwfn *p_hwfn,
 		     BIT(big_ram->is_256b_bit_offset[dev_data->chip_id]) ? 256
 									 : 128;
 
-	strncpy(type_name, big_ram->instance_name, BIG_RAM_NAME_LEN);
-	strncpy(mem_name, big_ram->instance_name, BIG_RAM_NAME_LEN);
+	memcpy(type_name, big_ram->instance_name, BIG_RAM_NAME_LEN);
+	memcpy(mem_name, big_ram->instance_name, BIG_RAM_NAME_LEN);
 
 	/* Dump memory header */
 	offset += qed_grc_dump_mem_hdr(p_hwfn,
@@ -6359,8 +6359,7 @@ static void qed_read_str_from_buf(void *buf, u32 *offset, u32 size, char *dest)
 {
 	const char *source_str = &((const char *)buf)[*offset];
 
-	strncpy(dest, source_str, size);
-	dest[size - 1] = '\0';
+	strscpy(dest, source_str, size);
 	*offset += size;
 }
 

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231011-strncpy-drivers-net-ethernet-qlogic-qed-qed_debug-c-211d594201e4

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH v2] qed: replace uses of strncpy

[Kees Cook]

On Thu, Oct 12, 2023 at 06:35:41PM +0000, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> This patch eliminates three uses of strncpy():
> 
> Firstly, `dest` is expected to be NUL-terminated which is evident by the
> manual setting of a NUL-byte at size - 1. For this use specifically,
> strscpy() is a viable replacement due to the fact that it guarantees
> NUL-termination on the destination buffer.
> 
> The next two cases should simply be memcpy() as the size of the src
> string is always 3 and the destination string just wants the first 3
> bytes changed.
> 
> To be clear, there are no buffer overread bugs in the current code as
> the sizes and offsets are carefully managed such that buffers are
> NUL-terminated. However, with these changes, the code is now more robust
> and less ambiguous (and hopefully easier to read).
> 
> 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
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Yup, this looks good to me now. Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH v2] qed: replace uses of strncpy

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 12 Oct 2023 18:35:41 +0000 you wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> This patch eliminates three uses of strncpy():
> 
> Firstly, `dest` is expected to be NUL-terminated which is evident by the
> manual setting of a NUL-byte at size - 1. For this use specifically,
> strscpy() is a viable replacement due to the fact that it guarantees
> NUL-termination on the destination buffer.
> 
> [...]

Here is the summary with links:
  - [v2] qed: replace uses of strncpy
    https://git.kernel.org/netdev/net-next/c/a02527363abb

You are awesome, thank you!
-- 
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