CVE-2021-47222: net: bridge: fix vlan tunnel dst refcnt when egressing
In the Linux kernel, the following vulnerability has been resolved:
net: bridge: fix vlan tunnel dst refcnt when egressing
The egress tunnel code uses dstclone() and directly sets the result which is wrong because the entry might have 0 refcnt or be already deleted, causing number of problems. It also triggers the WARNON() in dsthold()[1] when a refcnt couldn't be taken. Fix it by using dstholdsafe() and checking if a reference was actually taken before setting the dst.
[1] dmesg WARNON log and following refcnt errors WARNING: CPU: 5 PID: 38 at include/net/dst.h:230 brhandleegressvlantunnel+0x10b/0x134 [bridge] Modules linked in: 8021q garp mrp bridge stp llc bonding ipv6 virtionet CPU: 5 PID: 38 Comm: ksoftirqd/5 Kdump: loaded Tainted: G W 5.13.0-rc3+ #360 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014 RIP: 0010:brhandleegressvlantunnel+0x10b/0x134 [bridge] Code: e8 85 bc 01 e1 45 84 f6 74 90 45 31 f6 85 db 48 c7 c7 a0 02 19 a0 41 0f 94 c6 31 c9 31 d2 44 89 f6 e8 64 bc 01 e1 85 db 75 02 <0f> 0b 31 c9 31 d2 44 89 f6 48 c7 c7 70 02 19 a0 e8 4b bc 01 e1 49 RSP: 0018:ffff8881003d39e8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa01902a0 RBP: ffff8881040c6700 R08: 0000000000000000 R09: 0000000000000001 R10: 2ce93d0054fe0d00 R11: 54fe0d00000e0000 R12: ffff888109515000 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000401 FS: 0000000000000000(0000) GS:ffff88822bf40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f42ba70f030 CR3: 0000000109926000 CR4: 00000000000006e0 Call Trace: brhandlevlan+0xbc/0xca [bridge] brforward+0x23/0x164 [bridge] deliverclone+0x41/0x48 [bridge] brhandleframefinish+0x36f/0x3aa [bridge] ? skbdst+0x2e/0x38 [bridge] ? brhandleingressvlantunnel+0x3e/0x1c8 [bridge] ? brhandleframefinish+0x3aa/0x3aa [bridge] brhandleframe+0x2c3/0x377 [bridge] ? skbpull+0x33/0x51 ? vlandoreceive+0x4f/0x36a ? brhandleframefinish+0x3aa/0x3aa [bridge] netifreceiveskbcore+0x539/0x7c6 ? listdelentryvalid+0x16e/0x1c2 netifreceiveskblistcore+0x6d/0xd6 netifreceiveskblistinternal+0x1d9/0x1fa gronormallist+0x22/0x3e devgroreceive+0x55b/0x600 ? detachbufsplit+0x58/0x140 napigroreceive+0x94/0x12e virtnetpoll+0x15d/0x315 [virtionet] napipoll+0x2c/0x1c9 netrxaction+0xe6/0x1fb dosoftirq+0x115/0x2d8 runksoftirqd+0x18/0x20 smpbootthreadfn+0x183/0x19c ? smpbootunregisterpercputhread+0x66/0x66 kthread+0x10a/0x10f ? kthreadmoddelayedwork+0xb6/0xb6 retfromfork+0x22/0x30 ---[ end trace 49f61b07f775fd2b ]--- dstrelease: dst:00000000c02d677a refcnt:-1 dstrelease underflow
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Linux kernelto a version that resolves this vulnerability.Fixed in 5.13.0-rc3+ #360 - Configuration
Modify the bridge VLAN tunnel egress path (br_handle_egress_vlan_tunnel) to use dst_hold_safe() rather than dst_clone(), avoiding WARN_ON() in dst_hold() and preventing dst_release underflow when no refcount can be taken.
Linux kernel bridge (br_handle_egress_vlan_tunnel) dst_clone() replaced with dst_hold_safe() when egressing VLAN tunnel = use dst_hold_safe() instead of dst_clone() and directly setting the result
Event History
Frequently Asked Questions
What is the severity of CVE-2021-47222?
CVE-2021-47222 is classified as a medium severity vulnerability affecting the Linux kernel.
How do I fix CVE-2021-47222?
To fix CVE-2021-47222, you should update your Linux kernel to the latest version that addresses this vulnerability.
What versions of Linux Kernel are affected by CVE-2021-47222?
CVE-2021-47222 affects Linux Kernel versions starting from 5.13.0-rc3.
What is the nature of CVE-2021-47222?
CVE-2021-47222 involves a vulnerability in the egress tunnel code of the Linux kernel related to improper handling of destination reference counts.
Is CVE-2021-47222 exploitable?
Yes, CVE-2021-47222 can potentially be exploited, leading to stability issues in the affected systems.