Message-ID: <b141489b-780c-1753-2a83-ccb60c4554d0@oracle.com>
Date:   Wed, 8 Dec 2021 11:44:02 -0500
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Subject: Re: [PATCH] tun: avoid double free in tun_free_netdev
Content-Language: en-CA
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     Greg KH <gregkh@linuxfoundation.org>, davem@davemloft.net,
        kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1638974605-24085-1-git-send-email-george.kennedy@oracle.com>
 <YbDR/JStiIco3HQS@kroah.com>
 <022193b1-4ddd-f04e-aafa-ce249ec6d120@oracle.com>
 <20211208083614.61f386ad@hermes.local>
From:   George Kennedy <george.kennedy@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <20211208083614.61f386ad@hermes.local>
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On 12/8/2021 11:36 AM, Stephen Hemminger wrote:
> On Wed, 8 Dec 2021 11:29:47 -0500
> George Kennedy <george.kennedy@oracle.com> wrote:
>
>> On 12/8/2021 10:40 AM, Greg KH wrote:
>>> On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
>>>> Avoid double free in tun_free_netdev() by clearing tun->security
>>>> after free and using it to indicate that free has already been done.
>>>>
>>>> BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>>>
>>>> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
>>>> Hardware name: Red Hat KVM, BIOS
>>>> Call Trace:
>>>>    <TASK>
>>>>    __dump_stack lib/dump_stack.c:88 [inline]
>>>>    dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
>>>>    print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
>>>>    kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
>>>>    ____kasan_slab_free mm/kasan/common.c:346 [inline]
>>>>    __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
>>>>    kasan_slab_free include/linux/kasan.h:235 [inline]
>>>>    slab_free_hook mm/slub.c:1723 [inline]
>>>>    slab_free_freelist_hook mm/slub.c:1749 [inline]
>>>>    slab_free mm/slub.c:3513 [inline]
>>>>    kfree+0xac/0x2d0 mm/slub.c:4561
>>>>    selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>>>    security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>>>>    tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
>>>>    netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
>>>>    rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
>>>>    __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
>>>>    tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>>>>    vfs_ioctl fs/ioctl.c:51 [inline]
>>>>    __do_sys_ioctl fs/ioctl.c:874 [inline]
>>>>    __se_sys_ioctl fs/ioctl.c:860 [inline]
>>>>    __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>>>>    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>>>    do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>>>>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> Reported-by: syzkaller <syzkaller@googlegroups.com>
>>>> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
>>>> ---
>>>>    drivers/net/tun.c | 11 +++++++++--
>>>>    1 file changed, 9 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>>> index 1572878..617c71f 100644
>>>> --- a/drivers/net/tun.c
>>>> +++ b/drivers/net/tun.c
>>>> @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
>>>>    	dev->tstats = NULL;
>>>>    
>>>>    	tun_flow_uninit(tun);
>>>> -	security_tun_dev_free_security(tun->security);
>>>> +	if (tun->security) {
>>>> +		security_tun_dev_free_security(tun->security);
>>>> +		tun->security = NULL;
>>>> +	}
>>>>    	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
>>>>    	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
>>>>    }
>>>> @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>>>>    
>>>>    err_free_flow:
>>>>    	tun_flow_uninit(tun);
>>>> -	security_tun_dev_free_security(tun->security);
>>>> +	if (tun->security) {
>>>> +		security_tun_dev_free_security(tun->security);
>>>> +		/* Let tun_free_netdev() know the free has already been done. */
>>>> +		tun->security = NULL;
>>> What protects this from racing with tun_free_netdev()?
>> tun_free_netdev() is called after err_free_flow has already done the
>> free. rtnl_lock() and rtnl_unlock() prevent the race.
>>
>> Here is the full KASAN report:
>>
>> Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.
>>
>> ==================================================================
>> BUG: KASAN: double-free or invalid-free in
>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>
>> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
>> Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
>> 04/01/2014
>> Call Trace:
>>    <TASK>
>>    __dump_stack lib/dump_stack.c:88 [inline]
>>    dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
>>    print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
>>    kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
>>    ____kasan_slab_free mm/kasan/common.c:346 [inline]
>>    __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
>>    kasan_slab_free include/linux/kasan.h:235 [inline]
>>    slab_free_hook mm/slub.c:1723 [inline]
>>    slab_free_freelist_hook mm/slub.c:1749 [inline]
>>    slab_free mm/slub.c:3513 [inline]
>>    kfree+0xac/0x2d0 mm/slub.c:4561
>>    selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>    security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>>    tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
>>    netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
>>    rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
>>    __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
>>    tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>>    vfs_ioctl fs/ioctl.c:51 [inline]
>>    __do_sys_ioctl fs/ioctl.c:874 [inline]
>>    __se_sys_ioctl fs/ioctl.c:860 [inline]
>>    __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>>    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>    do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>> RIP: 0033:0x7fd496f4c289
>> Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 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 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
>> RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
>> RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
>> RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
>> R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
>>    </TASK>
>>
>> Allocated by task 25750:
>>    kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
>>    kasan_set_track mm/kasan/common.c:46 [inline]
>>    set_alloc_info mm/kasan/common.c:434 [inline]
>>    ____kasan_kmalloc mm/kasan/common.c:513 [inline]
>>    __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
>>    kasan_kmalloc include/linux/kasan.h:269 [inline]
>>    kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
>>    kmalloc include/linux/slab.h:590 [inline]
>>    kzalloc include/linux/slab.h:724 [inline]
>>    selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
>>    security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
>>    tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
>>    __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
>>    tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>>    vfs_ioctl fs/ioctl.c:51 [inline]
>>    __do_sys_ioctl fs/ioctl.c:874 [inline]
>>    __se_sys_ioctl fs/ioctl.c:860 [inline]
>>    __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>>    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>    do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Freed by task 25750:
>>    kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
>>    kasan_set_track+0x25/0x30 mm/kasan/common.c:46
>>    kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
>>    ____kasan_slab_free mm/kasan/common.c:366 [inline]
>>    ____kasan_slab_free mm/kasan/common.c:328 [inline]
>>    __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
>>    kasan_slab_free include/linux/kasan.h:235 [inline]
>>    slab_free_hook mm/slub.c:1723 [inline]
>>    slab_free_freelist_hook mm/slub.c:1749 [inline]
>>    slab_free mm/slub.c:3513 [inline]
>>    kfree+0xac/0x2d0 mm/slub.c:4561
>>    selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>    security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>>    tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
>>    __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
>>    tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>>    vfs_ioctl fs/ioctl.c:51 [inline]
>>    __do_sys_ioctl fs/ioctl.c:874 [inline]
>>    __se_sys_ioctl fs/ioctl.c:860 [inline]
>>    __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>>    do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>    do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>>    entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> The buggy address belongs to the object at ffff888066b87370
>>    which belongs to the cache kmalloc-8 of size 8
>> The buggy address is located 0 bytes inside of
>>    8-byte region [ffff888066b87370, ffff888066b87378)
>> The buggy address belongs to the page:
>> page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
>> index:0x0 pfn:0x66b87
>> flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
>> raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
>> raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>    ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
>>    ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
>>   >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
>>                                                                ^
>>    ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
>>    ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
>> ==================================================================
>>
>>> And why can't security_tun_dev_free_security() handle a NULL value?
>> security_tun_dev_free_security() could be modified to handle the NULL value.
> It looks like a lot of the problem is duplicate unwind.
> Why does err_free_flow, err_free_stat etc unwinds need to exist if
> the free_netdev is going to do same thing.
Maybe instead do not call security_tun_dev_free_security(tun->security) 
in err_free_flow if it's going to be done anyway in tun_free_netdev().

George