Subject: Re: [syzbot] KASAN: slab-out-of-bounds Write in copy_verifier_state

From: [email-masked]
Date: Tue, 20 Dec 2022 11:57:24 -0800

On 12/19, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    041fae9c105a Merge tag 'f2fs-for-6.2-rc1' of git://git.ker..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=136be5d0480000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e2f3d9d232a3cac5
> dashboard link: https://syzkaller.appspot.com/bug?extid=59af7bf76d795311da8c
> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1650d477880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1305f993880000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e228bf558f91/disk-041fae9c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/11eeb90801b7/vmlinux-041fae9c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/1f9651f3b5bd/bzImage-041fae9c.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email-masked]
> 
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in copy_array kernel/bpf/verifier.c:1072 [inline]
> BUG: KASAN: slab-out-of-bounds in copy_verifier_state+0x130/0xbe0 kernel/bpf/verifier.c:1250
> Write of size 80 at addr ffff888022c71000 by task syz-executor186/5067
> 
> CPU: 0 PID: 5067 Comm: syz-executor186 Not tainted 6.1.0-syzkaller-10971-g041fae9c105a #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x1e3/0x2d0 lib/dump_stack.c:106
>  print_address_description+0x74/0x340 mm/kasan/report.c:306
>  print_report+0x107/0x220 mm/kasan/report.c:417
>  kasan_report+0x139/0x170 mm/kasan/report.c:517
>  kasan_check_range+0x2a7/0x2e0 mm/kasan/generic.c:189
>  memcpy+0x3c/0x60 mm/kasan/shadow.c:66
>  copy_array kernel/bpf/verifier.c:1072 [inline]
>  copy_verifier_state+0x130/0xbe0 kernel/bpf/verifier.c:1250
>  pop_stack kernel/bpf/verifier.c:1314 [inline]
>  do_check+0x8e51/0x107b0 kernel/bpf/verifier.c:14031
>  do_check_common+0x909/0x1800 kernel/bpf/verifier.c:16289
>  do_check_main kernel/bpf/verifier.c:16352 [inline]
>  bpf_check+0x107e2/0x16170 kernel/bpf/verifier.c:16936
>  bpf_prog_load+0x1306/0x1be0 kernel/bpf/syscall.c:2619
>  __sys_bpf+0x396/0x6d0 kernel/bpf/syscall.c:4979
>  __do_sys_bpf kernel/bpf/syscall.c:5083 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5081 [inline]
>  __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:5081
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7ff1fb190c29
> Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffeaae55678 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff1fb190c29
> RDX: 0000000000000048 RSI: 0000000020000200 RDI: 0000000000000005
> RBP: 00007ff1fb154dd0 R08: 0000000000000000 R09: 0000000000000000
> R10: 00000000ffffffff R11: 0000000000000246 R12: 00007ff1fb154e60
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>  </TASK>
> 
> Allocated by task 5067:
>  kasan_save_stack mm/kasan/common.c:45 [inline]
>  kasan_set_track+0x4c/0x70 mm/kasan/common.c:52
>  ____kasan_kmalloc mm/kasan/common.c:371 [inline]
>  __kasan_krealloc+0xbf/0xf0 mm/kasan/common.c:439
>  kasan_krealloc include/linux/kasan.h:231 [inline]
>  __do_krealloc mm/slab_common.c:1361 [inline]
>  krealloc+0xb2/0x110 mm/slab_common.c:1398
>  push_jmp_history kernel/bpf/verifier.c:2592 [inline]
>  is_state_visited kernel/bpf/verifier.c:13552 [inline]
>  do_check+0x9433/0x107b0 kernel/bpf/verifier.c:13752
>  do_check_common+0x909/0x1800 kernel/bpf/verifier.c:16289
>  do_check_main kernel/bpf/verifier.c:16352 [inline]
>  bpf_check+0x107e2/0x16170 kernel/bpf/verifier.c:16936
>  bpf_prog_load+0x1306/0x1be0 kernel/bpf/syscall.c:2619
>  __sys_bpf+0x396/0x6d0 kernel/bpf/syscall.c:4979
>  __do_sys_bpf kernel/bpf/syscall.c:5083 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5081 [inline]
>  __x64_sys_bpf+0x78/0x90 kernel/bpf/syscall.c:5081
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> The buggy address belongs to the object at ffff888022c71000
>  which belongs to the cache kmalloc-96 of size 96
> The buggy address is located 0 bytes inside of
>  96-byte region [ffff888022c71000, ffff888022c71060)
> 
> The buggy address belongs to the physical page:
> page:ffffea00008b1c40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x22c71
> ksm flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000200 ffff888012841780 ffffea0000a6d880 0000000000000003
> raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY), pid 4437, tgid 4437 (udevd), ts 26581643327, free_ts 26581082061
>  prep_new_page mm/page_alloc.c:2531 [inline]
>  get_page_from_freelist+0x72b/0x7a0 mm/page_alloc.c:4283
>  __alloc_pages+0x259/0x560 mm/page_alloc.c:5549
>  alloc_slab_page+0xbd/0x190 mm/slub.c:1851
>  allocate_slab+0x5e/0x3c0 mm/slub.c:1998
>  new_slab mm/slub.c:2051 [inline]
>  ___slab_alloc+0x7f4/0xeb0 mm/slub.c:3193
>  __slab_alloc mm/slub.c:3292 [inline]
>  __slab_alloc_node mm/slub.c:3345 [inline]
>  slab_alloc_node mm/slub.c:3442 [inline]
>  __kmem_cache_alloc_node+0x25b/0x340 mm/slub.c:3491
>  __do_kmalloc_node mm/slab_common.c:967 [inline]
>  __kmalloc+0x9e/0x190 mm/slab_common.c:981
>  kmalloc include/linux/slab.h:584 [inline]
>  kzalloc include/linux/slab.h:720 [inline]
>  tomoyo_encode2 security/tomoyo/realpath.c:45 [inline]
>  tomoyo_encode+0x26f/0x540 security/tomoyo/realpath.c:80
>  tomoyo_realpath_from_path+0x5ae/0x5f0 security/tomoyo/realpath.c:283
>  tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
>  tomoyo_path_perm+0x280/0x680 security/tomoyo/file.c:822
>  security_inode_getattr+0xc0/0x140 security/security.c:1375
>  vfs_getattr fs/stat.c:161 [inline]
>  vfs_statx+0x198/0x4b0 fs/stat.c:236
>  vfs_fstatat fs/stat.c:270 [inline]
>  __do_sys_newfstatat fs/stat.c:440 [inline]
>  __se_sys_newfstatat+0x104/0x7b0 fs/stat.c:434
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> page last free stack trace:
>  reset_page_owner include/linux/page_owner.h:24 [inline]
>  free_pages_prepare mm/page_alloc.c:1446 [inline]
>  free_pcp_prepare+0x751/0x780 mm/page_alloc.c:1496
>  free_unref_page_prepare mm/page_alloc.c:3369 [inline]
>  free_unref_page+0x19/0x4c0 mm/page_alloc.c:3464
>  free_pipe_info+0x302/0x380 fs/pipe.c:851
>  put_pipe_info fs/pipe.c:711 [inline]
>  pipe_release+0x232/0x310 fs/pipe.c:734
>  __fput+0x3ba/0x880 fs/file_table.c:320
>  task_work_run+0x243/0x300 kernel/task_work.c:179
>  resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
>  exit_to_user_mode_loop+0x134/0x160 kernel/entry/common.c:171
>  exit_to_user_mode_prepare+0xad/0x110 kernel/entry/common.c:203
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
>  syscall_exit_to_user_mode+0x2e/0x60 kernel/entry/common.c:296
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Memory state around the buggy address:
>  ffff888022c70f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff888022c70f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff888022c71000: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>                          ^
>  ffff888022c71080: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>  ffff888022c71100: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> ==================================================================
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at [email-masked].
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 041fae9c105a
commit 589aa8077dcf413b06c78c6d8095496c98720c25
Author:     Stanislav Fomichev <[email-masked]>
AuthorDate: Tue Dec 20 11:51:17 2022 -0800
Commit:     Stanislav Fomichev <[email-masked]>
CommitDate: Tue Dec 20 11:51:17 2022 -0800

    Revert "mm: Make ksize() a reporting-only function"
    
    This reverts commit 38931d8989b5760b0bd17c9ec99e81986258e4cb.

diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
index 73684642c42d..0d59098f0876 100644
--- a/mm/kasan/kasan_test.c
+++ b/mm/kasan/kasan_test.c
@@ -783,30 +783,23 @@ static void kasan_global_oob_left(struct kunit *test)
 	KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
 }
 
-/* Check that ksize() does NOT unpoison whole object. */
+/* Check that ksize() makes the whole object accessible. */
 static void ksize_unpoisons_memory(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE - 5;
-	size_t real_size;
+	size_t size = 123, real_size;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
-
 	real_size = ksize(ptr);
-	KUNIT_EXPECT_GT(test, real_size, size);
 
 	OPTIMIZER_HIDE_VAR(ptr);
 
-	/* These accesses shouldn't trigger a KASAN report. */
-	ptr[0] = 'x';
-	ptr[size - 1] = 'x';
+	/* This access shouldn't trigger a KASAN report. */
+	ptr[size] = 'x';
 
-	/* These must trigger a KASAN report. */
-	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
-		KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
-	KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size + 5]);
-	KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size - 1]);
+	/* This one must. */
+	KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size]);
 
 	kfree(ptr);
 }
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 7e96abf1bd7d..33b1886b06eb 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1333,11 +1333,11 @@ __do_krealloc(const void *p, size_t new_size, gfp_t flags)
 	void *ret;
 	size_t ks;
 
-	/* Check for double-free before calling ksize. */
+	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
 	if (likely(!ZERO_OR_NULL_PTR(p))) {
 		if (!kasan_check_byte(p))
 			return NULL;
-		ks = ksize(p);
+		ks = kfence_ksize(p) ?: __ksize(p);
 	} else
 		ks = 0;
 
@@ -1405,10 +1405,8 @@ void kfree_sensitive(const void *p)
 	void *mem = (void *)p;
 
 	ks = ksize(mem);
-	if (ks) {
-		kasan_unpoison_range(mem, ks);
+	if (ks)
 		memzero_explicit(mem, ks);
-	}
 	kfree(mem);
 }
 EXPORT_SYMBOL(kfree_sensitive);
@@ -1429,11 +1427,13 @@ EXPORT_SYMBOL(kfree_sensitive);
  */
 size_t ksize(const void *objp)
 {
+	size_t size;
+
 	/*
-	 * We need to first check that the pointer to the object is valid.
-	 * The KASAN report printed from ksize() is more useful, then when
-	 * it's printed later when the behaviour could be undefined due to
-	 * a potential use-after-free or double-free.
+	 * We need to first check that the pointer to the object is valid, and
+	 * only then unpoison the memory. The report printed from ksize() is
+	 * more useful, then when it's printed later when the behaviour could
+	 * be undefined due to a potential use-after-free or double-free.
 	 *
 	 * We use kasan_check_byte(), which is supported for the hardware
 	 * tag-based KASAN mode, unlike kasan_check_read/write().
@@ -1447,7 +1447,13 @@ size_t ksize(const void *objp)
 	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !kasan_check_byte(objp))
 		return 0;
 
-	return kfence_ksize(objp) ?: __ksize(objp);
+	size = kfence_ksize(objp) ?: __ksize(objp);
+	/*
+	 * We assume that ksize callers could use whole allocated area,
+	 * so we need to unpoison this area.
+	 */
+	kasan_unpoison_range(objp, size);
+	return size;
 }
 EXPORT_SYMBOL(ksize);