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Fri, 27 Sep 2019 12:42:02 -0700 (PDT) MIME-Version: 1.0 References: <20190927034338.15813-1-walter-zh.wu@mediatek.com> <1569594142.9045.24.camel@mtksdccf07> In-Reply-To: <1569594142.9045.24.camel@mtksdccf07> From: Dmitry Vyukov Date: Fri, 27 Sep 2019 21:41:51 +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 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 w= rote: > > > > > > memmove() and memcpy() have missing underflow issues. > > > When -7 <=3D size < 0, then KASAN will miss to catch the underflow is= sue. > > > It looks like shadow start address and shadow end address is the 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, _RET_IP_)= ; > > > check_memory_region((unsigned long)dest, len, true, _RET_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 issue. > > > > > > [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_memse= t(void) > > > kfree(ptr); > > > } > > > > > > +static noinline void __init kmalloc_oob_in_memmove_underflow(void) > > > +{ > > > + 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(void) > > > +{ > > > + 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_poisoned_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 *)addr), > > > - kasan_mem_to_shadow((void *)addr + size - 1) = + 1); > > > + if ((long)size < 0) > > > + shadow_end =3D kasan_mem_to_shadow((void *)addr + siz= e); > > > > Hi Walter, > > > > Thanks for working on this. > > > > If size<0, does it make sense to continue at all? We will still check > > 1PB of shadow memory? What happens when we pass such huge range to > > memory_is_nonzero? > > Perhaps it's better to produce an error and bail out immediately if siz= e<0? > > I agree with what you said. when size<0, it is indeed an unreasonable > behavior, it should be blocked from continuing to do. > > > > Also, what's the failure mode of the tests? Didn't they badly corrupt > > 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 of > > 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 following.o= r? > > 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. But check_memory_region already returns a bool, so we could check that bool and return early. > + kasan_report_invalid_size(src, dest, len, _RET_IP_); > + > check_memory_region((unsigned long)src, len, false, _RET_IP_); > check_memory_region((unsigned long)dest, len, true, _RET_IP_); > > >