Messages in this thread Patch in this message | | | Date | Thu, 7 Sep 2023 14:28:05 -0700 | From | Bjorn Andersson <> | Subject | Re: [PATCH v2] arm64/sysreg: refactor deprecated strncpy |
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On Fri, Aug 11, 2023 at 04:33:51PM +0000, Justin Stitt wrote: > `strncpy` is deprecated for use on NUL-terminated destination strings > [1]. Which seems to be the case here due to the forceful setting of `buf`'s > tail to 0. > > 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 can simplify the logic and also check for any silent > truncation by using `strscpy`'s return value. > > This should have no functional change and yet uses a more robust and > less ambiguous interface whilst reducing code complexity. >
I'm sorry, but this patch is wrong.
__parse_cmdline() is supposed to match the command line against a set of keywords, one word at a time. The new implementation ignores the word-boundaries and matches the whole command line once and then breaks the loop, typically without having found a match. (See below)
Can we please have this patch dropped, Will?
Also, the commit message is a blanket statement about why strscpy is better than stncpy, but I don't see how this is applicable to the code it attempts to "fix". Afaict the code already handled these cases.
> Link: 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 > Suggested-by: Kees Cook <keescook@chromium.org> > Cc: linux-hardening@vger.kernel.org > Signed-off-by: Justin Stitt <justinstitt@google.com> > --- > Changes in v2: > - Utilize return value from strscpy and check for truncation (thanks Kees) > - Link to v1: https://lore.kernel.org/r/20230810-strncpy-arch-arm64-v1-1-f67f3685cd64@google.com > --- > For reference, see a part of `strscpy`'s implementation here: > > | /* Hit buffer length without finding a NUL; force NUL-termination. */ > | if (res) > | dest[res-1] = '\0'; > > Note: compile tested > --- > arch/arm64/kernel/idreg-override.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c > index 2fe2491b692c..aee12c75b738 100644 > --- a/arch/arm64/kernel/idreg-override.c > +++ b/arch/arm64/kernel/idreg-override.c > @@ -262,9 +262,9 @@ static __init void __parse_cmdline(const char *cmdline, bool parse_aliases) > if (!len) > return; > > - len = min(len, ARRAY_SIZE(buf) - 1);
Here "len" was either the number of bytes to the first space, the end of the string, or the last byte in "buf".
> - strncpy(buf, cmdline, len);
So this will copy one word, or the rest of the string.
> - buf[len] = 0;
And it will NUL-terminate the word, which is then matched upon below.
> + len = strscpy(buf, cmdline, ARRAY_SIZE(buf));
In this new implementation, the code copies the rest of the command line to "buf", makes an attempt to match with with the keywords, and then breaks the loop (as cmdline + len is the end of the string).
Regards, Bjorn
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