Re: [syzbot] [bpf?] WARNING in push_jmp_history

[Vlastimil Babka]

On 10/8/24 11:41, Eduard Zingerman wrote:
> On Tue, 2024-10-08 at 01:43 -0700, syzbot wrote:
>> syzbot has bisected this issue to:
>> 
>> commit d0a38fad51cc70ab3dd3c59b54d8079ac19220b9
>> Author: Feng Tang <feng.tang@xxxxxxxxx>
>> Date:   Wed Sep 11 06:45:34 2024 +0000
>> 
>>     mm/slub: Improve redzone check and zeroing for krealloc()
>> 
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11ddbb80580000
>> start commit:   c02d24a5af66 Add linux-next specific files for 20241003
>> git tree:       linux-next
>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13ddbb80580000
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15ddbb80580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=94f9caf16c0af42d
>> dashboard link: https://syzkaller.appspot.com/bug?extid=7e46cdef14bf496a3ab4
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10b82707980000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16f4c327980000
>> 
>> Reported-by: syzbot+7e46cdef14bf496a3ab4@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Fixes: d0a38fad51cc ("mm/slub: Improve redzone check and zeroing for krealloc()")
>> 
>> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 
> There are two issues demonstrated by this repro:
> - one is mm/slub related;
> - another one is verification taking forever.
> 
> About the mm/slub related. Applying the following patch with
> additional logging on top of commit d0a38fad51cc identified by syzbot:

The slab one is known from other reports and the problematic commit was
removed from -next since then.

> 
> ------- 8< ------------------------------------------------------------
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9a7ed527e47e..c1582a6d1d33 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3494,7 +3494,9 @@ static int push_jmp_history(struct bpf_verifier_env *env, struct bpf_verifier_st
>  
>         cnt++;
>         alloc_size = kmalloc_size_roundup(size_mul(cnt, sizeof(*p)));
> +       printk("push_jmp_history: #1 cur->jmp_history=%p\n", cur->jmp_history);
>         p = krealloc(cur->jmp_history, alloc_size, GFP_USER);
> +       printk("push_jmp_history: #2 cur->jmp_history=%p\n", p);
>         if (!p)
>                 return -ENOMEM;
>         cur->jmp_history = p;
> diff --git a/mm/slub.c b/mm/slub.c
> index e0fb0a26c796..3f5b080ac1f5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4627,7 +4627,7 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
>         struct slab *slab;
>  
>         slab = virt_to_slab(obj);
> -       if (WARN_ONCE(!slab, "%s: Object is not a Slab page!\n", __func__))
> +       if (WARN_ONCE(!slab, "%s: Object %p is not a Slab page!\n", __func__, obj))
>                 return NULL;
>         return slab->slab_cache;
>  }
> ------------------------------------------------------------ >8 -------
> 
> Produces the following log:
> 
>  l1: [    2.942120] push_jmp_history: #2 cur->jmp_history=00000000a0f6f503
>  l2: [    2.944445] push_jmp_history: #1 cur->jmp_history=00000000a0f6f503
>  l3: [    2.944560] ------------[ cut here ]------------
>  l4: [    2.944647] virt_to_cache: Object 00000000a0f6f503 is not a Slab page!
>  l5: [    2.944765] WARNING: CPU: 0 PID: 145 at mm/slub.c:4630 krealloc_noprof (mm/slub.c:4630 mm/slub.c:4728 mm/slub.c:4813) 
>  l6: [    2.944906] Modules linked in:
>  l7: [    2.945134] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014
>  l8: [    2.945285] RIP: 0010:krealloc_noprof (mm/slub.c:4630 mm/slub.c:4728 mm/slub.c:4813) 
>                ...
> l9:  [    2.952088] BUG: kernel NULL pointer dereference, address: 000000000000001c
> l10: [    2.952171] #PF: supervisor read access in kernel mode
> l11: [    2.952240] #PF: error_code(0x0000) - not-present page
> l12: [    2.952309] PGD 105d51067 P4D 105d51067 PUD 1013d0067 PMD 0 
> l13: [    2.952402] Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
> l14: [    2.952611] Tainted: [W]=WARN
> l15: [    2.952664] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014
> l16: [    2.952794] RIP: 0010:krealloc_noprof (mm/slub.c:0 mm/slub.c:4729 mm/slub.c:4813) 
> 
> Lines l{1,2,4} show that address 0xa0f6f503 was first allocated by
> krealloc and then krealloc failed to recognize it as such.
> 
> The warning at l3 is reported by virt_to_cache() called from
> __do_krealloc():
> 
> 
>    4715 static __always_inline __realloc_size(2) void *
>    4716 __do_krealloc(const void *p, size_t new_size, gfp_t flags)
>    4717 {
>    4718         void *ret;
>    4719         size_t ks;
>    4720         int orig_size = 0;
>    4721         struct kmem_cache *s;
>    4722 
>    4723         /* Check for double-free. */
>    4724         if (likely(!ZERO_OR_NULL_PTR(p))) {
>    4725                 if (!kasan_check_byte(p))
>    4726                         return NULL;
>    4727 
>    4728                 s = virt_to_cache(p);
>    4729                 orig_size = get_orig_size(s, (void *)p);
>    4730                 ks = s->object_size;
> 
> When virt_to_cache() reports the warning it returns NULL.
> Hence variable 's' at line 4728 is NULL and this causes null pointer
> dereference at line 4730, reported at l9.
> 
> Lines 4725-4730 were changed by commit d0a38fad51cc identified by syzbot,
> previously 'ks' was identified using other means.
> 
> Feng, this issue seem unrelated to BPF verifier, could you please take a look?
> 
> Best regards,
> Eduard
>