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Subject: Re: KASAN: invalid-free in p9_client_create
To:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+3a0f6c96e37e347c6ba9@syzkaller.appspotmail.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>
Cc:     Dominique Martinet <asmadeus@codewreck.org>,
        David Miller <davem@davemloft.net>,
        Eric Van Hensbergen <ericvh@gmail.com>,
        Jakub Kicinski <kuba@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Latchesar Ionkov <lucho@ionkov.net>,
        netdev <netdev@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        v9fs-developer@lists.sourceforge.net
References: <0000000000006ef45b05b436ddb4@google.com>
 <CACT4Y+aMw276FEUfS5+ZjJxxZqmFqM7=MnC7gWE9zn7vgha-AA@mail.gmail.com>
From:   "Xu, Yanfei" <yanfei.xu@windriver.com>
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Date:   Tue, 17 Nov 2020 20:46:27 +0800
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How about this patch? If it is appropriate, I will send a real one.

     mm/slub: fix slab double-free when release callback of sysfs trigger

     Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>

diff --git a/mm/slub.c b/mm/slub.c
index 4148235ba554..d10c4fbf8c84 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5653,7 +5653,7 @@ static int sysfs_slab_add(struct kmem_cache *s)
         s->kobj.kset = kset;
         err = kobject_init_and_add(&s->kobj, &slab_ktype, NULL, "%s", 
name);
         if (err) {
-               kobject_put(&s->kobj);
+               kfree_const(&s->kobj.name);
                 goto out;
         }
----------------------------------------------------------
Because a previous patch dde3c6b7(mm/slub: fix a memory leak in 
sysfs_slab_add()) added a kobject_put() in the error path of 
kobject_init_and_add(). It results the release callback of sysfs, which 
is kmem_cache_release(), is triggered when get into the error path.

However, we will also free the 'kmem_cache' and 'kmem_cache_node' and 
'kmem_cache->name' at the error path of create_cache() when 
kobject_init_and_add() returns failure. That makes double-free.

About the patch which introduced this issue, I think we could fix it by 
freeing the leaked memory directly instead of adding kobject_put（）.

Regards,
Yanfei


On 11/16/20 7:11 PM, Dmitry Vyukov wrote:
> [Please note this e-mail is from an EXTERNAL e-mail address]
> 
> 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
>> ==================================================================
>>
>>
>> ---
>> This report is generated by a bot. It may contain errors.
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