netdev - Re: [PATCH v8 1/8] Get rid of __get_task

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <202408281712.F78440FF@keescook>
Date: Wed, 28 Aug 2024 17:17:55 -0700
From: Kees Cook <kees@...nel.org>
To: Alejandro Colomar <alx@...nel.org>
Cc: Yafang Shao <laoar.shao@...il.com>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, justinstitt@...gle.com,
	ebiederm@...ssion.com, alexei.starovoitov@...il.com,
	rostedt@...dmis.org, catalin.marinas@....com,
	penguin-kernel@...ove.sakura.ne.jp, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	audit@...r.kernel.org, linux-security-module@...r.kernel.org,
	selinux@...r.kernel.org, bpf@...r.kernel.org,
	netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	Matus Jokay <matus.jokay@...ba.sk>,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH v8 1/8] Get rid of __get_task_comm()

On Wed, Aug 28, 2024 at 05:09:08PM +0200, Alejandro Colomar wrote:
> Hi Kees,
> 
> On Wed, Aug 28, 2024 at 06:48:39AM GMT, Kees Cook wrote:
> 
> [...]
> 
> > >Thank you for your suggestion. How does the following commit log look
> > >to you? Does it meet your expectations?
> > >
> > >    string: Use ARRAY_SIZE() in strscpy()
> > >
> > >    We can use ARRAY_SIZE() instead to clarify that they are regular characters.
> > >
> > >    Co-developed-by: Alejandro Colomar <alx@...nel.org>
> > >    Signed-off-by: Alejandro Colomar <alx@...nel.org>
> > >    Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> > >
> > >diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
> > >index bbab79c0c074..07216996e3a9 100644
> > >--- a/arch/um/include/shared/user.h
> > >+++ b/arch/um/include/shared/user.h
> > >@@ -14,7 +14,7 @@
> > >  * copying too much infrastructure for my taste, so userspace files
> > >  * get less checking than kernel files.
> > >  */
> > >-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
> > >+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x))
> > >
> > > /* This is to get size_t and NULL */
> > > #ifndef __UM_HOST__
> > >@@ -60,7 +60,7 @@ static inline void print_hex_dump(const char *level,
> > >const char *prefix_str,
> > > extern int in_aton(char *str);
> > > extern size_t strlcat(char *, const char *, size_t);
> > > extern size_t sized_strscpy(char *, const char *, size_t);
> > >-#define strscpy(dst, src)      sized_strscpy(dst, src, sizeof(dst))
> > >+#define strscpy(dst, src)      sized_strscpy(dst, src, ARRAY_SIZE(dst))
> > 
> > Uh, but why? strscpy() copies bytes, not array elements. Using sizeof() is already correct and using ARRAY_SIZE() could lead to unexpectedly small counts (in admittedly odd situations).
> > 
> > What is the problem you're trying to solve here?
> 
> I suggested that here:
> <https://lore.kernel.org/all/2jxak5v6dfxlpbxhpm3ey7oup4g2lnr3ueurfbosf5wdo65dk4@srb3hsk72zwq/>
> 
> There, you'll find the rationale (and also for avoiding the _pad calls
> where not necessary --I ignore if it's necessary here--).

Right, so we only use byte strings for strscpy(), so sizeof() is
sufficient. There's no technical need to switch to ARRAY_SIZE(), and I'd
like to minimize any changes to such core APIs without a good reason.

And for the _pad change, we are also doing strncpy() replacement via
case-by-case analysis, but with a common function like get_task_comm(),
I don't want to change the behavior without a complete audit of the
padding needs of every caller. Since that's rather a lot for this series,
I'd rather we just leave the existing behavior as-is, and if padding
removal is wanted after that, we can do it on a case-by-case basis then.

-Kees

-- 
Kees Cook