CVE-2021-47448

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

mptcp: fix possible stall on recvmsg()

recvmsg() can enter an infinite loop if the caller provides the

MSG_WAITALL, the data present in the receive queue is not sufficient to

fulfill the request, and no more data is received by the peer.

When the above happens, mptcp_wait_data() will always return with

no wait, as the MPTCP_DATA_READY flag checked by such function is

set and never cleared in such code path.

Leveraging the above syzbot was able to trigger an RCU stall:

rcu: INFO: rcu_preempt self-detected stall on CPU

rcu: 0-...!: (10499 ticks this GP) idle=0af/1/0x4000000000000000 softirq=10678/10678 fqs=1

(t=10500 jiffies g=13089 q=109)

rcu: rcu_preempt kthread starved for 10497 jiffies! g13089 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1

rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.

rcu: RCU grace-period kthread stack dump:

task:rcu_preempt state:R running task stack:28696 pid: 14 ppid: 2 flags:0x00004000

Call Trace:

context_switch kernel/sched/core.c:4955 [inline]

__schedule+0x940/0x26f0 kernel/sched/core.c:6236

schedule+0xd3/0x270 kernel/sched/core.c:6315

schedule_timeout+0x14a/0x2a0 kernel/time/timer.c:1881

rcu_gp_fqs_loop+0x186/0x810 kernel/rcu/tree.c:1955

rcu_gp_kthread+0x1de/0x320 kernel/rcu/tree.c:2128

kthread+0x405/0x4f0 kernel/kthread.c:327

ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

rcu: Stack dump where RCU GP kthread last ran:

Sending NMI from CPU 0 to CPUs 1:

NMI backtrace for cpu 1

CPU: 1 PID: 8510 Comm: syz-executor827 Not tainted 5.15.0-rc2-next-20210920-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

RIP: 0010:bytes_is_nonzero mm/kasan/generic.c:84 [inline]

RIP: 0010:memory_is_nonzero mm/kasan/generic.c:102 [inline]

RIP: 0010:memory_is_poisoned_n mm/kasan/generic.c:128 [inline]

RIP: 0010:memory_is_poisoned mm/kasan/generic.c:159 [inline]

RIP: 0010:check_region_inline mm/kasan/generic.c:180 [inline]

RIP: 0010:kasan_check_range+0xc8/0x180 mm/kasan/generic.c:189

Code: 38 00 74 ed 48 8d 50 08 eb 09 48 83 c0 01 48 39 d0 74 7a 80 38 00 74 f2 48 89 c2 b8 01 00 00 00 48 85 d2 75 56 5b 5d 41 5c c3 <48> 85 d2 74 5e 48 01 ea eb 09 48 83 c0 01 48 39 d0 74 50 80 38 00

RSP: 0018:ffffc9000cd676c8 EFLAGS: 00000283

RAX: ffffed100e9a110e RBX: ffffed100e9a110f RCX: ffffffff88ea062a

RDX: 0000000000000001 RSI: 0000000000000008 RDI: ffff888074d08870

RBP: ffffed100e9a110e R08: 0000000000000001 R09: ffff888074d08877

R10: ffffed100e9a110e R11: 0000000000000000 R12: ffff888074d08000

R13: ffff888074d08000 R14: ffff888074d08088 R15: ffff888074d08000

FS: 0000555556d8e300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000

S: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000020000180 CR3: 0000000068909000 CR4: 00000000001506e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

instrument_atomic_read_write include/linux/instrumented.h:101 [inline]

test_and_clear_bit include/asm-generic/bitops/instrumented-atomic.h:83 [inline]

mptcp_release_cb+0x14a/0x210 net/mptcp/protocol.c:3016

release_sock+0xb4/0x1b0 net/core/sock.c:3204

mptcp_wait_data net/mptcp/protocol.c:1770 [inline]

mptcp_recvmsg+0xfd1/0x27b0 net/mptcp/protocol.c:2080

inet6_recvmsg+0x11b/0x5e0 net/ipv6/af_inet6.c:659

sock_recvmsg_nosec net/socket.c:944 [inline]

____sys_recvmsg+0x527/0x600 net/socket.c:2626

___sys_recvmsg+0x127/0x200 net/socket.c:2670

do_recvmmsg+0x24d/0x6d0 net/socket.c:2764

__sys_recvmmsg net/socket.c:2843 [inline]

__do_sys_recvmmsg net/socket.c:2866 [inline]

__se_sys_recvmmsg net/socket.c:2859 [inline]

__x64_sys_recvmmsg+0x20b/0x260 net/socket.c:2859

do_syscall_x64 arch/x86/entry/common.c:50 [inline]

do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80

entry_SYSCALL_64_after_hwframe+0x44/0xae

RIP: 0033:0x7fc200d2

---truncated---