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    SubjectRe: [PATCH] kasan: fix the missing underflow in memmove and memcpy with CONFIG_KASAN_GENERIC=y
    On Thu, Oct 3, 2019 at 3:51 PM Walter Wu <walter-zh.wu@mediatek.com> wrote:>
    > how about this?
    >
    > commit fd64691026e7ccb8d2946d0804b0621ac177df38
    > Author: Walter Wu <walter-zh.wu@mediatek.com>
    > Date: Fri Sep 27 09:54:18 2019 +0800
    >
    > kasan: detect invalid 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.
    >
    > KASAN report:
    >
    > BUG: KASAN: invalid size 18446744073709551614 in
    > kmalloc_memmove_invalid_size+0x70/0xa0
    >
    > CPU: 1 PID: 91 Comm: cat Not tainted
    > 5.3.0-rc1ajb-00001-g31943bbc21ce-dirty #7
    > Hardware name: linux,dummy-virt (DT)
    > Call trace:
    > dump_backtrace+0x0/0x278
    > show_stack+0x14/0x20
    > dump_stack+0x108/0x15c
    > print_address_description+0x64/0x368
    > __kasan_report+0x108/0x1a4
    > kasan_report+0xc/0x18
    > check_memory_region+0x15c/0x1b8
    > memmove+0x34/0x88
    > kmalloc_memmove_invalid_size+0x70/0xa0
    >
    > [1] https://bugzilla.kernel.org/show_bug.cgi?id=199341
    >
    > Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
    > Reported-by: Dmitry Vyukov <dvyukov@google.com>
    >
    > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
    > index b63b367a94e8..e4e517a51860 100644
    > --- a/lib/test_kasan.c
    > +++ b/lib/test_kasan.c
    > @@ -280,6 +280,23 @@ 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;
    > @@ -734,6 +751,7 @@ 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 2277b82902d8..5fd377af7457 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;

    Overall approach looks good to me.
    A good question is what we should return here. All bets are off after
    a report, but we still try to "minimize damage". One may argue for
    returning addr here and in other functions. But the more I think about
    this, the more I think it does not matter.


    > 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_);
    >
    > 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/report.c b/mm/kasan/report.c
    > index 0e5f965f1882..0cd317ef30f5 100644
    > --- a/mm/kasan/report.c
    > +++ b/mm/kasan/report.c
    > @@ -68,11 +68,16 @@ __setup("kasan_multi_shot", kasan_set_multi_shot);
    >
    > 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).


    > + } else {
    > + 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));
    > + }
    > }
    >
    > static DEFINE_SPINLOCK(report_lock);
    > 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);
    >
    > /*
    >
    >
    > --
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