Re: KASAN: invalid-free in p9_client_create

[Dmitry Vyukov <dvyukov@google.com>]

On Mon, Nov 16, 2020 at 11:30 AM syzbot
<syzbot+3a0f6c96e37e347c6ba9@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    92edc4ae Add linux-next specific files for 20201113
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=142f8816500000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=79ad4f8ad2d96176
> dashboard link: https://syzkaller.appspot.com/bug?extid=3a0f6c96e37e347c6ba9
> compiler:       gcc (GCC) 10.1.0-syz 20200507
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3a0f6c96e37e347c6ba9@syzkaller.appspotmail.com

Looks like a real double free in slab code. +MM maintainers
Note there was a preceding kmalloc failure in sysfs_slab_add.


> RBP: 00007fa358076ca0 R08: 0000000020000080 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000001f
> R13: 00007fff7dcf224f R14: 00007fa3580779c0 R15: 000000000118bf2c
> kobject_add_internal failed for 9p-fcall-cache (error: -12 parent: slab)
> ==================================================================
> BUG: KASAN: double-free or invalid-free in slab_free mm/slub.c:3157 [inline]
> BUG: KASAN: double-free or invalid-free in kmem_cache_free+0x82/0x350 mm/slub.c:3173
>
> CPU: 0 PID: 15981 Comm: syz-executor.5 Not tainted 5.10.0-rc3-next-20201113-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x107/0x163 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:230
>  kasan_report_invalid_free+0x51/0x80 mm/kasan/report.c:355
>  ____kasan_slab_free+0x100/0x110 mm/kasan/common.c:352
>  kasan_slab_free include/linux/kasan.h:194 [inline]
>  slab_free_hook mm/slub.c:1548 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1586
>  slab_free mm/slub.c:3157 [inline]
>  kmem_cache_free+0x82/0x350 mm/slub.c:3173
>  create_cache mm/slab_common.c:274 [inline]
>  kmem_cache_create_usercopy+0x2ab/0x300 mm/slab_common.c:357
>  p9_client_create+0xc4d/0x10c0 net/9p/client.c:1063
>  v9fs_session_init+0x1dd/0x1770 fs/9p/v9fs.c:406
>  v9fs_mount+0x79/0x9b0 fs/9p/vfs_super.c:126
>  legacy_get_tree+0x105/0x220 fs/fs_context.c:592
>  vfs_get_tree+0x89/0x2f0 fs/super.c:1549
>  do_new_mount fs/namespace.c:2896 [inline]
>  path_mount+0x12ae/0x1e70 fs/namespace.c:3227
>  do_mount fs/namespace.c:3240 [inline]
>  __do_sys_mount fs/namespace.c:3448 [inline]
>  __se_sys_mount fs/namespace.c:3425 [inline]
>  __x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x45deb9
> Code: 0d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 db b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fa358076c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 0000000000021800 RCX: 000000000045deb9
> RDX: 0000000020000100 RSI: 0000000020000040 RDI: 0000000000000000
> RBP: 00007fa358076ca0 R08: 0000000020000080 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000001f
> R13: 00007fff7dcf224f R14: 00007fa3580779c0 R15: 000000000118bf2c
>
> Allocated by task 15981:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:39
>  kasan_set_track mm/kasan/common.c:47 [inline]
>  set_alloc_info mm/kasan/common.c:403 [inline]
>  ____kasan_kmalloc.constprop.0+0x82/0xa0 mm/kasan/common.c:434
>  kasan_slab_alloc include/linux/kasan.h:211 [inline]
>  slab_post_alloc_hook mm/slab.h:512 [inline]
>  slab_alloc_node mm/slub.c:2903 [inline]
>  slab_alloc mm/slub.c:2911 [inline]
>  kmem_cache_alloc+0x12a/0x470 mm/slub.c:2916
>  kmem_cache_zalloc include/linux/slab.h:672 [inline]
>  create_cache mm/slab_common.c:251 [inline]
>  kmem_cache_create_usercopy+0x1a6/0x300 mm/slab_common.c:357
>  p9_client_create+0xc4d/0x10c0 net/9p/client.c:1063
>  v9fs_session_init+0x1dd/0x1770 fs/9p/v9fs.c:406
>  v9fs_mount+0x79/0x9b0 fs/9p/vfs_super.c:126
>  legacy_get_tree+0x105/0x220 fs/fs_context.c:592
>  vfs_get_tree+0x89/0x2f0 fs/super.c:1549
>  do_new_mount fs/namespace.c:2896 [inline]
>  path_mount+0x12ae/0x1e70 fs/namespace.c:3227
>  do_mount fs/namespace.c:3240 [inline]
>  __do_sys_mount fs/namespace.c:3448 [inline]
>  __se_sys_mount fs/namespace.c:3425 [inline]
>  __x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Freed by task 15981:
>  kasan_save_stack+0x1b/0x40 mm/kasan/common.c:39
>  kasan_set_track+0x1c/0x30 mm/kasan/common.c:47
>  kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:359
>  ____kasan_slab_free+0xe1/0x110 mm/kasan/common.c:373
>  kasan_slab_free include/linux/kasan.h:194 [inline]
>  slab_free_hook mm/slub.c:1548 [inline]
>  slab_free_freelist_hook+0x5d/0x150 mm/slub.c:1586
>  slab_free mm/slub.c:3157 [inline]
>  kmem_cache_free+0x82/0x350 mm/slub.c:3173
>  kobject_cleanup lib/kobject.c:705 [inline]
>  kobject_release lib/kobject.c:736 [inline]
>  kref_put include/linux/kref.h:65 [inline]
>  kobject_put+0x1c8/0x540 lib/kobject.c:753
>  sysfs_slab_add+0x164/0x1d0 mm/slub.c:5656
>  __kmem_cache_create+0x471/0x5a0 mm/slub.c:4476
>  create_cache mm/slab_common.c:262 [inline]
>  kmem_cache_create_usercopy+0x1ed/0x300 mm/slab_common.c:357
>  p9_client_create+0xc4d/0x10c0 net/9p/client.c:1063
>  v9fs_session_init+0x1dd/0x1770 fs/9p/v9fs.c:406
>  v9fs_mount+0x79/0x9b0 fs/9p/vfs_super.c:126
>  legacy_get_tree+0x105/0x220 fs/fs_context.c:592
>  vfs_get_tree+0x89/0x2f0 fs/super.c:1549
>  do_new_mount fs/namespace.c:2896 [inline]
>  path_mount+0x12ae/0x1e70 fs/namespace.c:3227
>  do_mount fs/namespace.c:3240 [inline]
>  __do_sys_mount fs/namespace.c:3448 [inline]
>  __se_sys_mount fs/namespace.c:3425 [inline]
>  __x64_sys_mount+0x27f/0x300 fs/namespace.c:3425
>  do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The buggy address belongs to the object at ffff888013a45b40
>  which belongs to the cache kmem_cache of size 224
> The buggy address is located 0 bytes inside of
>  224-byte region [ffff888013a45b40, ffff888013a45c20)
> The buggy address belongs to the page:
> page:00000000cfbbc7ff refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888013a45c80 pfn:0x13a45
> flags: 0xfff00000000200(slab)
> raw: 00fff00000000200 dead000000000100 dead000000000122 ffff888010041000
> raw: ffff888013a45c80 00000000800c0004 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>  ffff888013a45a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888013a45a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
> >ffff888013a45b00: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>                                            ^
>  ffff888013a45b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff888013a45c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
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