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um: vector: refactor deprecated strncpy 

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on its destination buffer argument which is
_not_ the case for `strncpy`!

In this case, we are able to drop the now superfluous `... - 1`
instances because `strscpy` will automatically truncate the last byte by
setting it to a NUL byte if the source size exceeds the destination size
or if the source string is not NUL-terminated.

I've also opted to remove the seemingly useless char* casts. I'm not
sure why they're present at all since (after expanding the `ifr_name`
macro) `ifr.ifr_ifrn.ifrn_name` is a char* already.

All in all, `strscpy` is a more robust and less ambiguous interface
while also letting us remove some `... -1`'s which cleans things up a
bit.

[1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
[2]: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html

Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Link: https://lore.kernel.org/r/20230807-arch-um-drivers-v1-1-10d602c5577a@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Justin Stitt 2023-08-07 18:22:30 +00:00 committed by Kees Cook
parent 967afdf808
commit 30bed99e0c
1 changed files with 2 additions and 2 deletions
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4
arch/um/drivers/vector_user.c
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@ -141,7 +141,7 @@ static int create_tap_fd(char *iface)
}
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
err = ioctl(fd, TUNSETIFF, (void *) &ifr);
if (err != 0) {
@ -171,7 +171,7 @@ static int create_raw_fd(char *iface, int flags, int proto)
goto raw_fd_cleanup;
}
memset(&ifr, 0, sizeof(ifr));
strncpy((char *)&ifr.ifr_name, iface, sizeof(ifr.ifr_name) - 1);
strscpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name));
if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
err = -errno;
goto raw_fd_cleanup;