[PATCH] net: bonding: Use strscpy() instead of manually-truncated strncpy()

Silence this warning by just using strscpy() directly:

drivers/net/bonding/bond_main.c:4877:3: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
    4877 |   strncpy(params->primary, primary, IFNAMSIZ);
         |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: kernel test robot <redacted>
Link: https://lore.kernel.org/lkml/202102150705.fdR6obB0-lkp@intel.com
Signed-off-by: Kees Cook <redacted>
---
 drivers/net/bonding/bond_main.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c5a646d06102..ecfc48f2d0d0 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -5329,10 +5329,8 @@ static int bond_check_params(struct bond_params *params)
 			(struct reciprocal_value) { 0 };
 	}
 
-	if (primary) {
-		strncpy(params->primary, primary, IFNAMSIZ);
-		params->primary[IFNAMSIZ - 1] = 0;
-	}
+	if (primary)
+		strscpy(params->primary, primary, sizeof(params->primary));
 
 	memcpy(params->arp_targets, arp_target, sizeof(arp_target));
 

-- 
2.25.1

Would it make sense to also replace the other strncpy in the same file.

Shoaib

On 6/2/21 11:11 AM, Kees Cook wrote:

On Wed, Jun 02, 2021 at 12:46:46PM -0700, Rao Shoaib wrote:

Would it make sense to also replace the other strncpy in the same file.

                strncpy(ifr.ifr_name, slave_dev->name, IFNAMSIZ);

I couldn't tell if this was a non-string, if it needed padding, etc. The
one I fixed below appears to be null-terminated? (Though now that I look
at it, perhaps it should be using strscpy_pad().)

And there are a bunch of other manual truncations in the kernel on
ifr_name:

$ git grep ifr_name | grep 'IFNAMSIZ.*=.*0'
drivers/net/tun.c:              ifr.ifr_name[IFNAMSIZ-1] = '\0';
net/core/dev_ioctl.c:   ifr->ifr_name[IFNAMSIZ-1] = 0;
net/core/dev_ioctl.c:   ifr->ifr_name[IFNAMSIZ-1] = 0;
net/decnet/dn_dev.c:    ifr->ifr_name[IFNAMSIZ-1] = 0;
net/ieee802154/socket.c:        ifr.ifr_name[IFNAMSIZ-1] = 0;
net/ipv4/devinet.c:     ifr->ifr_name[IFNAMSIZ - 1] = 0;
net/wireless/wext-core.c:       iwr.ifr_name[IFNAMSIZ-1] = 0;
tools/lib/bpf/xsk.c:    ifr.ifr_name[IFNAMSIZ - 1] = '\0';

And given the copy_to_user() that might happen, I think this should
absolutely be strscpy_pad(). I will send a v2...

-Kees

Shoaib

On 6/2/21 11:11 AM, Kees Cook wrote:

quoted

Silence this warning by just using strscpy() directly:

drivers/net/bonding/bond_main.c:4877:3: warning: 'strncpy' specified bound 16 equals destination size [-Wstringop-truncation]
     4877 |   strncpy(params->primary, primary, IFNAMSIZ);
          |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Reported-by: kernel test robot <redacted>
Link: https://lore.kernel.org/lkml/202102150705.fdR6obB0-lkp@intel.com
Signed-off-by: Kees Cook <redacted>
---
  drivers/net/bonding/bond_main.c | 6 ++----
  1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index c5a646d06102..ecfc48f2d0d0 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c

@@ -5329,10 +5329,8 @@ static int bond_check_params(struct bond_params *params)
  			(struct reciprocal_value) { 0 };
  	}
-	if (primary) {
-		strncpy(params->primary, primary, IFNAMSIZ);
-		params->primary[IFNAMSIZ - 1] = 0;
-	}
+	if (primary)
+		strscpy(params->primary, primary, sizeof(params->primary));
  	memcpy(params->arp_targets, arp_target, sizeof(arp_target));

-- 
Kees Cook