CVE-2021-47014

In the Linux kernel, the following vulnerability has been resolved:

net/sched: act_ct: fix wild memory access when clearing fragments

while testing re-assembly/re-fragmentation using act_ct, it's possible to

observe a crash like the following one:

KASAN: maybe wild-memory-access in range [0x0001000000000448-0x000100000000044f]

CPU: 50 PID: 0 Comm: swapper/50 Tainted: G S 5.12.0-rc7+ #424

Hardware name: Dell Inc. PowerEdge R730/072T6D, BIOS 2.4.3 01/17/2017

RIP: 0010:inet_frag_rbtree_purge+0x50/0xc0

Code: 00 fc ff df 48 89 c3 31 ed 48 89 df e8 a9 7a 38 ff 4c 89 fe 48 89 df 49 89 c6 e8 5b 3a 38 ff 48 8d 7b 40 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 75 59 48 8d bb d0 00 00 00 4c 8b 6b 40 48 89 f8 48

RSP: 0018:ffff888c31449db8 EFLAGS: 00010203

RAX: 0000200000000089 RBX: 000100000000040e RCX: ffffffff989eb960

RDX: 0000000000000140 RSI: ffffffff97cfb977 RDI: 000100000000044e

RBP: 0000000000000900 R08: 0000000000000000 R09: ffffed1186289350

R10: 0000000000000003 R11: ffffed1186289350 R12: dffffc0000000000

R13: 000100000000040e R14: 0000000000000000 R15: ffff888155e02160

FS: 0000000000000000(0000) GS:ffff888c31440000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00005600cb70a5b8 CR3: 0000000a2c014005 CR4: 00000000003706e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

<IRQ>

inet_frag_destroy+0xa9/0x150

call_timer_fn+0x2d/0x180

run_timer_softirq+0x4fe/0xe70

__do_softirq+0x197/0x5a0

irq_exit_rcu+0x1de/0x200

sysvec_apic_timer_interrupt+0x6b/0x80

</IRQ>

when act_ct temporarily stores an IP fragment, restoring the skb qdisc cb

results in putting random data in FRAG_CB(), and this causes those "wild"

memory accesses later, when the rbtree is purged. Never overwrite the skb

cb in case tcf_ct_handle_fragments() returns -EINPROGRESS.