linux-kernel - Re: [PATCH] selftests/mm: compaction_test: Fix off by one in check

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20ad879e-689b-4b09-823c-4cb4f9b010e7@stanley.mountain>
Date: Fri, 9 Aug 2024 23:01:38 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Shuah Khan <skhan@...uxfoundation.org>
Cc: Dev Jain <dev.jain@....com>, Andrew Morton <akpm@...ux-foundation.org>,
	Shuah Khan <shuah@...nel.org>, linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] selftests/mm: compaction_test: Fix off by one in
 check_compaction()

On Fri, Aug 09, 2024 at 11:20:48AM -0600, Shuah Khan wrote:
> On 8/9/24 06:32, Dan Carpenter wrote:
> > The "initial_nr_hugepages" variable is unsigned long so it takes up to
> > 20 characters to print, plus 1 more character for the NUL terminator.
> > Unfortunately, this buffer is not quite large enough for the terminator
> > to fit.  Also use snprintf() for a belt and suspenders approach.
> > 
> > Fixes: fb9293b6b015 ("selftests/mm: compaction_test: fix bogus test success and reduce probability of OOM-killer invocation")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> > ---
> >   tools/testing/selftests/mm/compaction_test.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
> > index e140558e6f53..2c3a0eb6b22d 100644
> > --- a/tools/testing/selftests/mm/compaction_test.c
> > +++ b/tools/testing/selftests/mm/compaction_test.c
> > @@ -89,9 +89,10 @@ int check_compaction(unsigned long mem_free, unsigned long hugepage_size,
> >   	int fd, ret = -1;
> >   	int compaction_index = 0;
> >   	char nr_hugepages[20] = {0};
> > -	char init_nr_hugepages[20] = {0};
> > +	char init_nr_hugepages[24] = {0};
> 
> Can we exceed this limit too? Can you make this a define?
> 

It's based on counting the digits in U64_MAX.

18446744073709551615X
123456789012345678901

We don't have any defines for that kind of thing.  It's not a bad idea.
#define STRLEN_U64_MAX 20
char init_nr_hugepages[STRLEN_U64_MAX + 1];

But it should be done as part of a kernel wide clean up and not part of this
buffer overflow fix.  The line above it could be changed as well, for example.
Let me create a KTODO and hope the internet will take care of it.

KTODO: create defines for STRLEN_[SU]8/16/32/64_MIN/MAX.

Btw, I rounded up to 24 just because I like buffer sizes that are divisible
by 4 but the compiler is probably going to do that automatically either way.

regards,
dan carpenter