Messages in this thread Patch in this message | | | From | Yann Droneaud <> | Date | Wed, 27 Jul 2016 15:51:57 +0200 | Subject | Re: [kernel-hardening] [RFC patch 1/6] random: Simplify API for random address requests |
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Hi,
Le mardi 26 juillet 2016 à 03:01 +0000, Jason Cooper a écrit : > To date, all callers of randomize_range() have set the length to 0, > and check for a zero return value. For the current callers, the only > way to get zero returned is if end <= start. Since they are all > adding a constant to the start address, this is unnecessary. >
I agree.
> We can remove a bunch of needless checks by simplifying the API to do > just what everyone wants, return an address between [start, start + > range]. >
I agree.
For the record:
http://lkml.kernel.org/r/cover.1390770607.git.ydroneaud@opteya.com
> While we're here, s/get_random_int/get_random_long/. No current call > site is adversely affected by get_random_int(), since all current > range requests are < MAX_UINT. However, we should match caller > expectations to avoid coming up short (ha!) in the future. > > Signed-off-by: Jason Cooper <jason@lakedaemon.net> > --- > drivers/char/random.c | 17 ++++------------- > include/linux/random.h | 2 +- > 2 files changed, 5 insertions(+), 14 deletions(-) > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0158d3bff7e5..1251cb2cbab2 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1822,22 +1822,13 @@ unsigned long get_random_long(void) > EXPORT_SYMBOL(get_random_long); > > /* > - * randomize_range() returns a start address such that > - * > - * [...... <range> .....] > - * start end > - * > - * a <range> with size "len" starting at the return value is inside > in the > - * area defined by [start, end], but is otherwise randomized. > + * randomize_addr() returns a page aligned address within [start, > start + > + * range] > */ > unsigned long > -randomize_range(unsigned long start, unsigned long end, unsigned > long len) > +randomize_addr(unsigned long start, unsigned long range) > { > - unsigned long range = end - len - start; > - > - if (end <= start + len) > - return 0; > - return PAGE_ALIGN(get_random_int() % range + start); > + return PAGE_ALIGN(get_random_long() % range + start); > } > > /* Interface for in-kernel drivers of true hardware RNGs. > diff --git a/include/linux/random.h b/include/linux/random.h > index e47e533742b5..1ad877a98186 100644 > --- a/include/linux/random.h > +++ b/include/linux/random.h > @@ -34,7 +34,7 @@ extern const struct file_operations random_fops, > urandom_fops; > > unsigned int get_random_int(void); > unsigned long get_random_long(void); > -unsigned long randomize_range(unsigned long start, unsigned long > end, unsigned long len); > +unsigned long randomize_addr(unsigned long start, unsigned long > range); > > u32 prandom_u32(void); > void prandom_bytes(void *buf, size_t nbytes);
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