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Fri, 04 Oct 2019 02:54:16 -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> <1570069078.19702.57.camel@mtksdccf07> <1570095525.19702.59.camel@mtksdccf07> <1570110681.19702.64.camel@mtksdccf07> <1570164140.19702.97.camel@mtksdccf07> <1570176131.19702.105.camel@mtksdccf07> <1570182257.19702.109.camel@mtksdccf07> In-Reply-To: <1570182257.19702.109.camel@mtksdccf07> From: Dmitry Vyukov Date: Fri, 4 Oct 2019 11:54:04 +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, Oct 4, 2019 at 11:44 AM Walter Wu wrote: > > On Fri, 2019-10-04 at 11:18 +0200, Dmitry Vyukov wrote: > > On Fri, Oct 4, 2019 at 10:02 AM Walter Wu wrote: > > > > > > On Fri, 2019-10-04 at 12:42 +0800, Walter Wu wrote: > > > > On Thu, 2019-10-03 at 16:53 +0200, Dmitry Vyukov wrote: > > > > > On Thu, Oct 3, 2019 at 3:51 PM Walter Wu wrote:> > > > > > > > > > > > > static void print_error_description(struct kasan_access_info *info) > > > > > > { > > > > > > - pr_err("BUG: KASAN: %s in %pS\n", > > > > > > - get_bug_type(info), (void *)info->ip); > > > > > > - pr_err("%s of size %zu at addr %px by task %s/%d\n", > > > > > > - info->is_write ? "Write" : "Read", info->access_size, > > > > > > - info->access_addr, current->comm, task_pid_nr(current)); > > > > > > + if ((long)info->access_size < 0) { > > > > > > + pr_err("BUG: KASAN: invalid size %zu in %pS\n", > > > > > > + info->access_size, (void *)info->ip); > > > > > > > > > > I would not introduce a new bug type. > > > > > These are parsed and used by some systems, e.g. syzbot. If size is > > > > > user-controllable, then a new bug type for this will mean 2 bug > > > > > reports. > > > > > It also won't harm to print Read/Write, definitely the address, so no > > > > > reason to special case this out of a dozen of report formats. > > > > > This can qualify as out-of-bounds (definitely will cross some > > > > > bounds!), so I would change get_bug_type() to return > > > > > "slab-out-of-bounds" (as the most common OOB) in such case (with a > > > > > comment). > > > > > > > > > Print Read/Write and address information, it is ok. > > > > But if we can directly point to the root cause of this problem, why we > > > > not do it? see 1) and 2) to get a point, if we print OOB, then user > > > > needs one minute to think what is root case of this problem, but if we > > > > print invalid size, then user can directly get root case. this is my > > > > original thinking. > > > > 1)Invalid size is true then OOB is true. > > > > 2)OOB is true then invalid size may be true or false. > > > > > > > > But I see you say some systems have used bug report so that avoid this > > > > trouble, i will print the wrong type is "out-of-bound" in a unified way > > > > when size<0. > > > > > > > > > > Updated my patch, please help to review it. > > > thanks. > > > > > > commit 13e10a7e4264eb25c5a14193068027afc9c261f6 > > > Author: Walter-zh Wu > > > Date: Fri Oct 4 15:27:17 2019 +0800 > > > > > > kasan: detect negative size in memory operation function > > > > > > It is an undefined behavior to pass a negative value to > > > memset()/memcpy()/memmove() > > > , so need to be detected by KASAN. > > > > > > If size is negative value, then it will be larger than ULONG_MAX/2, > > > so that we will qualify as out-of-bounds issue. > > > > > > KASAN report: > > > > > > BUG: KASAN: out-of-bounds in kmalloc_memmove_invalid_size+0x70/0xa0 > > > Read of size 18446744073709551608 at addr ffffff8069660904 by task > > > cat/72 > > > > > > CPU: 2 PID: 72 Comm: cat Not tainted > > > 5.4.0-rc1-next-20191004ajb-00001-gdb8af2f372b2-dirty #1 > > > Hardware name: linux,dummy-virt (DT) > > > Call trace: > > > dump_backtrace+0x0/0x288 > > > show_stack+0x14/0x20 > > > dump_stack+0x10c/0x164 > > > print_address_description.isra.9+0x68/0x378 > > > __kasan_report+0x164/0x1a0 > > > kasan_report+0xc/0x18 > > > check_memory_region+0x174/0x1d0 > > > memmove+0x34/0x88 > > > kmalloc_memmove_invalid_size+0x70/0xa0 > > > > > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=199341 > > > > > > Signed-off-by: Walter Wu > > > Reported -by: Dmitry Vyukov > > > Suggested-by: Dmitry Vyukov > > > > > > diff --git a/lib/test_kasan.c b/lib/test_kasan.c > > > index 49cc4d570a40..06942cf585cc 100644 > > > --- a/lib/test_kasan.c > > > +++ b/lib/test_kasan.c > > > @@ -283,6 +283,23 @@ static noinline void __init > > > kmalloc_oob_in_memset(void) > > > kfree(ptr); > > > } > > > > > > +static noinline void __init kmalloc_memmove_invalid_size(void) > > > +{ > > > + char *ptr; > > > + size_t size = 64; > > > + > > > + pr_info("invalid size 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_uaf(void) > > > { > > > char *ptr; > > > @@ -773,6 +790,7 @@ static int __init kmalloc_tests_init(void) > > > kmalloc_oob_memset_4(); > > > kmalloc_oob_memset_8(); > > > kmalloc_oob_memset_16(); > > > + kmalloc_memmove_invalid_size(); > > > kmalloc_uaf(); > > > kmalloc_uaf_memset(); > > > kmalloc_uaf2(); > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > > > index 6814d6d6a023..97dd6eecc3e7 100644 > > > --- a/mm/kasan/common.c > > > +++ b/mm/kasan/common.c > > > @@ -102,7 +102,8 @@ EXPORT_SYMBOL(__kasan_check_write); > > > #undef memset > > > void *memset(void *addr, int c, size_t len) > > > { > > > - check_memory_region((unsigned long)addr, len, true, _RET_IP_); > > > + if (!check_memory_region((unsigned long)addr, len, true, _RET_IP_)) > > > + return NULL; > > > > > > return __memset(addr, c, len); > > > } > > > @@ -110,7 +111,8 @@ void *memset(void *addr, int c, size_t len) > > > #undef memmove > > > 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_)) > > > + return NULL; > > > check_memory_region((unsigned long)dest, len, true, _RET_IP_); > > > > I would check both calls. > > The current code seems to be over-specialized for handling of invalid > > size (you assume that if it's invalid size, then the first > > check_memory_region will detect it and checking the second one is > > pointless, right?). > > But check_memory_region can return false in other cases too. > > Also seeing first call checked, but the second not checked just hurts > > my eyes when reading code (whenever I will read such code my first > > reaction will be "why?"). > > > I can't agree with you any more about second point. > > #undef memmove > void *memmove(void *dest, const void *src, size_t len) > { > if (!check_memory_region((unsigned long)src, len, false, _RET_IP_) > ||) > !check_memory_region((unsigned long)dest, len, true, _RET_IP_); > return NULL; > > return __memmove(dest, src, len); > } > > > > > > > > > return __memmove(dest, src, len); > > > @@ -119,7 +121,8 @@ void *memmove(void *dest, const void *src, size_t > > > len) > > > #undef memcpy > > > void *memcpy(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_)) > > > + return NULL; > > > check_memory_region((unsigned long)dest, len, true, _RET_IP_); > > > > > > return __memcpy(dest, src, len); > > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > > > index 616f9dd82d12..02148a317d27 100644 > > > --- a/mm/kasan/generic.c > > > +++ b/mm/kasan/generic.c > > > @@ -173,6 +173,11 @@ static __always_inline bool > > > check_memory_region_inline(unsigned long addr, > > > if (unlikely(size == 0)) > > > return true; > > > > > > + if (unlikely((long)size < 0)) { > > > + kasan_report(addr, size, write, ret_ip); > > > + return false; > > > + } > > > + > > > if (unlikely((void *)addr < > > > kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) { > > > kasan_report(addr, size, write, ret_ip); > > > diff --git a/mm/kasan/generic_report.c b/mm/kasan/generic_report.c > > > index 36c645939bc9..ae9596210394 100644 > > > --- a/mm/kasan/generic_report.c > > > +++ b/mm/kasan/generic_report.c > > > @@ -107,6 +107,13 @@ static const char *get_wild_bug_type(struct > > > kasan_access_info *info) > > > > > > const char *get_bug_type(struct kasan_access_info *info) > > > { > > > + /* > > > + * if access_size < 0, then it will be larger than ULONG_MAX/2, > > > + * so that this can qualify as out-of-bounds. > > > + */ > > > + if ((long)info->access_size < 0) > > > + return "out-of-bounds"; > > > > "out-of-bounds" is the _least_ frequent KASAN bug type. So saying > > "out-of-bounds" has downsides of both approaches and won't prevent > > duplicate reports by syzbot... > > > maybe i should add your comment into the comment in get_bug_type? Yes, that's exactly what I meant above: "I would change get_bug_type() to return "slab-out-of-bounds" (as the most common OOB) in such case (with a comment)." ;) > > > + > > > if (addr_has_shadow(info->access_addr)) > > > return get_shadow_bug_type(info); > > > return get_wild_bug_type(info); > > > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c > > > index 0e987c9ca052..b829535a3ad7 100644 > > > --- a/mm/kasan/tags.c > > > +++ b/mm/kasan/tags.c > > > @@ -86,6 +86,11 @@ bool check_memory_region(unsigned long addr, size_t > > > size, bool write, > > > if (unlikely(size == 0)) > > > return true; > > > > > > + if (unlikely((long)size < 0)) { > > > + kasan_report(addr, size, write, ret_ip); > > > + return false; > > > + } > > > + > > > tag = get_tag((const void *)addr); > > > > > > /* > > > diff --git a/mm/kasan/tags_report.c b/mm/kasan/tags_report.c > > > index 969ae08f59d7..1e1ca81214b5 100644 > > > --- a/mm/kasan/tags_report.c > > > +++ b/mm/kasan/tags_report.c > > > @@ -36,6 +36,13 @@ > > > > > > const char *get_bug_type(struct kasan_access_info *info) > > > { > > > + /* > > > + * if access_size < 0, then it will be larger than ULONG_MAX/2, > > > + * so that this can qualify as out-of-bounds. > > > + */ > > > + if ((long)info->access_size < 0) > > > + return "out-of-bounds"; > > > + > > > #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > > struct kasan_alloc_meta *alloc_meta; > > > struct kmem_cache *cache;