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: ------- 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
