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Fri, 27 Sep 2019 06:07:37 -0700 (PDT) MIME-Version: 1.0 References: <20190927034338.15813-1-walter-zh.wu@mediatek.com> In-Reply-To: <20190927034338.15813-1-walter-zh.wu@mediatek.com> From: Dmitry Vyukov Date: Fri, 27 Sep 2019 15:07:25 +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" 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 5:43 AM Walter Wu wrote: > > memmove() and memcpy() have missing underflow issues. > When -7 <= size < 0, then KASAN will miss to catch the underflow issue. > 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 = 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=199341 > > 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(void) > +{ > + char *ptr; > + size_t size = 64; > + > + pr_info("underflow out-of-bounds in memmove\n"); > + ptr = 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 = 64; > + > + pr_info("overflow out-of-bounds in memmove\n"); > + ptr = 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 = kasan_mem_to_shadow((void *)addr); > + void *shadow_end = kasan_mem_to_shadow((void *)addr + size - 1) + 1; > > - ret = memory_is_nonzero(kasan_mem_to_shadow((void *)addr), > - kasan_mem_to_shadow((void *)addr + size - 1) + 1); > + if ((long)size < 0) > + shadow_end = 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 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 size<0? 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. > + ret = memory_is_nonzero(shadow_start, shadow_end); > > if (unlikely(ret)) { > unsigned long last_byte = addr + size - 1; > -- > 2.18.0 > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20190927034338.15813-1-walter-zh.wu%40mediatek.com.