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@xxxxxxxxxx>
> > ---
> > 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
