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Wed, 02 Oct 2019 06:57:28 -0700 (PDT) MIME-Version: 1.0 References: <20190927034338.15813-1-walter-zh.wu@mediatek.com> <1569594142.9045.24.camel@mtksdccf07> <1569818173.17361.19.camel@mtksdccf07> <1570018513.19702.36.camel@mtksdccf07> In-Reply-To: <1570018513.19702.36.camel@mtksdccf07> From: Dmitry Vyukov Date: Wed, 2 Oct 2019 15:57:16 +0200 Message-ID: Subject: Re: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y To: Walter Wu Cc: Andrey Ryabinin , Alexander Potapenko , Matthias Brugger , LKML , kasan-dev , Linux-MM , Linux ARM , linux-mediatek@lists.infradead.org, wsd_upstream Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Oct 2, 2019 at 2:15 PM Walter Wu wrote: > > On Mon, 2019-09-30 at 12:36 +0800, Walter Wu wrote: > > On Fri, 2019-09-27 at 21:41 +0200, Dmitry Vyukov wrote: > > > On Fri, Sep 27, 2019 at 4:22 PM Walter Wu = wrote: > > > > > > > > On Fri, 2019-09-27 at 15:07 +0200, Dmitry Vyukov wrote: > > > > > On Fri, Sep 27, 2019 at 5:43 AM Walter Wu wrote: > > > > > > > > > > > > memmove() and memcpy() have missing underflow issues. > > > > > > When -7 <=3D size < 0, then KASAN will miss to catch the underf= low issue. > > > > > > It looks like shadow start address and shadow end address is th= e same, > > > > > > so it does not actually check anything. > > > > > > > > > > > > The following test is indeed not caught by KASAN: > > > > > > > > > > > > char *p =3D kmalloc(64, GFP_KERNEL); > > > > > > memset((char *)p, 0, 64); > > > > > > memmove((char *)p, (char *)p + 4, -2); > > > > > > kfree((char*)p); > > > > > > > > > > > > It should be checked here: > > > > > > > > > > > > void *memmove(void *dest, const void *src, size_t len) > > > > > > { > > > > > > check_memory_region((unsigned long)src, len, false, _RE= T_IP_); > > > > > > check_memory_region((unsigned long)dest, len, true, _RE= T_IP_); > > > > > > > > > > > > return __memmove(dest, src, len); > > > > > > } > > > > > > > > > > > > We fix the shadow end address which is calculated, then generic= KASAN > > > > > > get the right shadow end address and detect this underflow issu= e. > > > > > > > > > > > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=3D199341 > > > > > > > > > > > > Signed-off-by: Walter Wu > > > > > > Reported-by: Dmitry Vyukov > > > > > > --- > > > > > > lib/test_kasan.c | 36 ++++++++++++++++++++++++++++++++++++ > > > > > > mm/kasan/generic.c | 8 ++++++-- > > > > > > 2 files changed, 42 insertions(+), 2 deletions(-) > > > > > > > > > > > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > > > > > > index b63b367a94e8..8bd014852556 100644 > > > > > > --- a/lib/test_kasan.c > > > > > > +++ b/lib/test_kasan.c > > > > > > @@ -280,6 +280,40 @@ static noinline void __init kmalloc_oob_in= _memset(void) > > > > > > kfree(ptr); > > > > > > } > > > > > > > > > > > > +static noinline void __init kmalloc_oob_in_memmove_underflow(v= oid) > > > > > > +{ > > > > > > + char *ptr; > > > > > > + size_t size =3D 64; > > > > > > + > > > > > > + pr_info("underflow out-of-bounds in memmove\n"); > > > > > > + ptr =3D kmalloc(size, GFP_KERNEL); > > > > > > + if (!ptr) { > > > > > > + pr_err("Allocation failed\n"); > > > > > > + return; > > > > > > + } > > > > > > + > > > > > > + memset((char *)ptr, 0, 64); > > > > > > + memmove((char *)ptr, (char *)ptr + 4, -2); > > > > > > + kfree(ptr); > > > > > > +} > > > > > > + > > > > > > +static noinline void __init kmalloc_oob_in_memmove_overflow(vo= id) > > > > > > +{ > > > > > > + char *ptr; > > > > > > + size_t size =3D 64; > > > > > > + > > > > > > + pr_info("overflow out-of-bounds in memmove\n"); > > > > > > + ptr =3D kmalloc(size, GFP_KERNEL); > > > > > > + if (!ptr) { > > > > > > + pr_err("Allocation failed\n"); > > > > > > + return; > > > > > > + } > > > > > > + > > > > > > + memset((char *)ptr, 0, 64); > > > > > > + memmove((char *)ptr + size, (char *)ptr, 2); > > > > > > + kfree(ptr); > > > > > > +} > > > > > > + > > > > > > static noinline void __init kmalloc_uaf(void) > > > > > > { > > > > > > char *ptr; > > > > > > @@ -734,6 +768,8 @@ static int __init kmalloc_tests_init(void) > > > > > > kmalloc_oob_memset_4(); > > > > > > kmalloc_oob_memset_8(); > > > > > > kmalloc_oob_memset_16(); > > > > > > + kmalloc_oob_in_memmove_underflow(); > > > > > > + kmalloc_oob_in_memmove_overflow(); > > > > > > kmalloc_uaf(); > > > > > > kmalloc_uaf_memset(); > > > > > > kmalloc_uaf2(); > > > > > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > > > > > > index 616f9dd82d12..34ca23d59e67 100644 > > > > > > --- a/mm/kasan/generic.c > > > > > > +++ b/mm/kasan/generic.c > > > > > > @@ -131,9 +131,13 @@ static __always_inline bool memory_is_pois= oned_n(unsigned long addr, > > > > > > size_t size) > > > > > > { > > > > > > unsigned long ret; > > > > > > + void *shadow_start =3D kasan_mem_to_shadow((void *)addr= ); > > > > > > + void *shadow_end =3D kasan_mem_to_shadow((void *)addr += size - 1) + 1; > > > > > > > > > > > > - ret =3D memory_is_nonzero(kasan_mem_to_shadow((void *)a= ddr), > > > > > > - kasan_mem_to_shadow((void *)addr + size= - 1) + 1); > > > > > > + if ((long)size < 0) > > > > > > + shadow_end =3D kasan_mem_to_shadow((void *)addr= + size); > > > > > > > > > > Hi Walter, > > > > > > > > > > Thanks for working on this. > > > > > > > > > > If size<0, does it make sense to continue at all? We will still c= heck > > > > > 1PB of shadow memory? What happens when we pass such huge range t= o > > > > > memory_is_nonzero? > > > > > Perhaps it's better to produce an error and bail out immediately = if size<0? > > > > > > > > I agree with what you said. when size<0, it is indeed an unreasonab= le > > > > behavior, it should be blocked from continuing to do. > > > > > > > > > > > > > Also, what's the failure mode of the tests? Didn't they badly cor= rupt > > > > > memory? We tried to keep tests such that they produce the KASAN > > > > > reports, but don't badly corrupt memory b/c/ we need to run all o= f > > > > > them. > > > > > > > > Maybe we should first produce KASAN reports and then go to execute > > > > memmove() or do nothing? It looks like it=E2=80=99s doing the follo= wing.or? > > > > > > > > void *memmove(void *dest, const void *src, size_t len) > > > > { > > > > + if (long(len) <=3D 0) > > > > > > /\/\/\/\/\/\ > > > > > > This check needs to be inside of check_memory_region, otherwise we > > > will have similar problems in all other places that use > > > check_memory_region. > > Thanks for your reminder. > > > > bool check_memory_region(unsigned long addr, size_t size, bool write, > > unsigned long ret_ip) > > { > > + if (long(size) < 0) { > > + kasan_report_invalid_size(src, dest, len, _RET_IP_); > > + return false; > > + } > > + > > return check_memory_region_inline(addr, size, write, ret_ip); > > } > > > > > But check_memory_region already returns a bool, so we could check tha= t > > > bool and return early. > > > > When size<0, we should only show one KASAN report, and should we only > > limit to return when size<0 is true? If yse, then __memmove() will do > > nothing. > > > > > > void *memmove(void *dest, const void *src, size_t len) > > { > > - check_memory_region((unsigned long)src, len, false, _RET_IP_); > > + if(!check_memory_region((unsigned long)src, len, false, > > _RET_IP_) > > + && long(size) < 0) > > + return; > > + > > check_memory_region((unsigned long)dest, len, true, _RET_IP_); > > > > return __memmove(dest, src, len); > > > > > > Hi Dmitry, > > What do you think the following code is better than the above one. > In memmmove/memset/memcpy, they need to determine whether size < 0 is > true. we directly determine whether size is negative in memmove and > return early. it avoid to generate repeated KASAN report. Is it better? > > void *memmove(void *dest, const void *src, size_t len) > { > + if (long(size) < 0) { > + kasan_report_invalid_size(src, dest, len, _RET_IP_); > + return; > + } > + > check_memory_region((unsigned long)src, len, false, _RET_IP_); > check_memory_region((unsigned long)dest, len, true, _RET_IP_); > > > check_memory_region() still has to check whether the size is negative. > but memmove/memset/memcpy generate invalid size KASAN report will not be > there. If check_memory_region() will do the check, why do we need to duplicate it inside of memmove and all other range functions? I would do: void *memmove(void *dest, const void *src, size_t len) { if (check_memory_region((unsigned long)src, len, false, _RET_IP_)) return; This avoids duplicating the check, adds minimal amount of code to range functions and avoids adding kasan_report_invalid_size.