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Date:   Wed, 11 Oct 2023 22:20:10 +0000
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Message-ID: <20231011-strncpy-drivers-net-ethernet-qlogic-qed-qed_debug-c-v1-1-60c9ca2d54a2@google.com>
Subject: [PATCH] qed: replace uses of strncpy
From:   Justin Stitt <justinstitt@google.com>
To:     Ariel Elior <aelior@marvell.com>,
        Manish Chopra <manishc@marvell.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-hardening@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        Justin Stitt <justinstitt@google.com>
Content-Type: text/plain; charset="utf-8"
Precedence: bulk

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 changes utilizes snprintf() to make the copying behavior
more obvious. Previously, strncpy() was used to overwrite the first 3
characters of mem_name and type_name by setting a length argument less
than the size of the buffers themselves. This enables, in a roundabout
way, creating a string like "ASD_BIG_RAM" or "ASD_RAM". Let's just use
snprintf() with a precision specifier to hold the name prefix to exactly
3 characters long.

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>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/ethernet/qlogic/qed/qed_debug.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/qed/qed_debug.c b/drivers/net/ethernet/qlogic/qed/qed_debug.c
index cdcead614e9f..0a4fd1b04353 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_debug.c
+++ b/drivers/net/ethernet/qlogic/qed/qed_debug.c
@@ -3192,8 +3192,8 @@ static u32 qed_grc_dump_big_ram(struct qed_hwfn *p_hwfn,
 {
 	struct dbg_tools_data *dev_data = &p_hwfn->dbg_info;
 	u32 block_size, ram_size, offset = 0, reg_val, i;
-	char mem_name[12] = "???_BIG_RAM";
-	char type_name[8] = "???_RAM";
+	char mem_name[12];
+	char type_name[8];
 	struct big_ram_defs *big_ram;
 
 	big_ram = &s_big_ram_defs[big_ram_id];
@@ -3204,8 +3204,11 @@ 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);
+	snprintf(mem_name, sizeof(mem_name), "%.*s_BIG_RAM",
+		 BIG_RAM_NAME_LEN, big_ram->instance_name);
+
+	snprintf(type_name, sizeof(type_name), "%.*s_RAM",
+		 BIG_RAM_NAME_LEN, big_ram->instance_name);
 
 	/* Dump memory header */
 	offset += qed_grc_dump_mem_hdr(p_hwfn,
@@ -6359,8 +6362,7 @@ 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>