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Message-ID: <f8bb62a7-5845-53ed-7fbe-c0557c2745f2@basealt.ru>
Date: Thu, 11 Apr 2024 18:30:22 +0300
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User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
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Subject: Re: [PATCH net] Bluetooth: hci_event: fix double hci_conn_drop() when
 conn->state == BT_CONNECTED
Content-Language: en-US
To: marcel@holtmann.org, johan.hedberg@gmail.com, luiz.dentz@gmail.com,
 linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: lvc-project@linuxtesting.org, nickel@altlinux.org,
 oficerovas@altlinux.org, dutyrok@altlinux.org, stable@vger.kernel.org
References: <20240411151810.403167-1-kovalev@altlinux.org>
From: kovalev@altlinux.org
In-Reply-To: <20240411151810.403167-1-kovalev@altlinux.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

11.04.2024 18:18, kovalev@altlinux.org wrote:
> From: Vasiliy Kovalev <kovalev@altlinux.org>
> 
> There is no need to drop the connection of some functions in which the
> conn->state in BT_CONNECTED is marked, since in the future the same check
> takes place (for example, in the hci_encrypt_change_evt() function) and
> the hci_conn_drop() is called.
> 
> Otherwise, the conn->refcnt will become below zero, which will trigger a
> warning and may cause a crash on kernels with the panic_on_warn parameter
> enabled.
> 
repro.c generated by syzkaller:

#define _GNU_SOURCE

#include <dirent.h>
#include <endian.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/prctl.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#include <linux/capability.h>
#include <linux/rfkill.h>

static void sleep_ms(uint64_t ms)
{
         usleep(ms * 1000);
}

static uint64_t current_time_ms(void)
{
         struct timespec ts;
         if (clock_gettime(CLOCK_MONOTONIC, &ts))
         exit(1);
         return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
}

static bool write_file(const char* file, const char* what, ...)
{
         char buf[1024];
         va_list args;
         va_start(args, what);
         vsnprintf(buf, sizeof(buf), what, args);
         va_end(args);
         buf[sizeof(buf) - 1] = 0;
         int len = strlen(buf);
         int fd = open(file, O_WRONLY | O_CLOEXEC);
         if (fd == -1)
                 return false;
         if (write(fd, buf, len) != len) {
                 int err = errno;
                 close(fd);
                 errno = err;
                 return false;
         }
         close(fd);
         return true;
}

#define MAX_FDS 30

#define BTPROTO_HCI 1
#define ACL_LINK 1
#define SCAN_PAGE 2

typedef struct {
         uint8_t b[6];
} __attribute__((packed)) bdaddr_t;

#define HCI_COMMAND_PKT 1
#define HCI_EVENT_PKT 4
#define HCI_VENDOR_PKT 0xff

struct hci_command_hdr {
         uint16_t opcode;
         uint8_t plen;
} __attribute__((packed));

struct hci_event_hdr {
         uint8_t evt;
         uint8_t plen;
} __attribute__((packed));

#define HCI_EV_CONN_COMPLETE 0x03
struct hci_ev_conn_complete {
         uint8_t status;
         uint16_t handle;
         bdaddr_t bdaddr;
         uint8_t link_type;
         uint8_t encr_mode;
} __attribute__((packed));

#define HCI_EV_CONN_REQUEST 0x04
struct hci_ev_conn_request {
         bdaddr_t bdaddr;
         uint8_t dev_class[3];
         uint8_t link_type;
} __attribute__((packed));

#define HCI_EV_REMOTE_FEATURES 0x0b
struct hci_ev_remote_features {
         uint8_t status;
         uint16_t handle;
         uint8_t features[8];
} __attribute__((packed));

#define HCI_EV_CMD_COMPLETE 0x0e
struct hci_ev_cmd_complete {
         uint8_t ncmd;
         uint16_t opcode;
} __attribute__((packed));

#define HCI_OP_WRITE_SCAN_ENABLE 0x0c1a

#define HCI_OP_READ_BUFFER_SIZE 0x1005
struct hci_rp_read_buffer_size {
         uint8_t status;
         uint16_t acl_mtu;
         uint8_t sco_mtu;
         uint16_t acl_max_pkt;
         uint16_t sco_max_pkt;
} __attribute__((packed));

#define HCI_OP_READ_BD_ADDR 0x1009
struct hci_rp_read_bd_addr {
         uint8_t status;
         bdaddr_t bdaddr;
} __attribute__((packed));

#define HCI_EV_LE_META 0x3e
struct hci_ev_le_meta {
         uint8_t subevent;
} __attribute__((packed));

#define HCI_EV_LE_CONN_COMPLETE 0x01
struct hci_ev_le_conn_complete {
         uint8_t status;
         uint16_t handle;
         uint8_t role;
         uint8_t bdaddr_type;
         bdaddr_t bdaddr;
         uint16_t interval;
         uint16_t latency;
         uint16_t supervision_timeout;
         uint8_t clk_accurancy;
} __attribute__((packed));

struct hci_dev_req {
         uint16_t dev_id;
         uint32_t dev_opt;
};

struct vhci_vendor_pkt {
         uint8_t type;
         uint8_t opcode;
         uint16_t id;
};

#define HCIDEVUP _IOW('H', 201, int)
#define HCISETSCAN _IOW('H', 221, int)

static int vhci_fd = -1;

static void rfkill_unblock_all()
{
         int fd = open("/dev/rfkill", O_WRONLY);
         if (fd < 0)
         exit(1);
         struct rfkill_event event = {0};
         event.idx = 0;
         event.type = RFKILL_TYPE_ALL;
         event.op = RFKILL_OP_CHANGE_ALL;
         event.soft = 0;
         event.hard = 0;
         if (write(fd, &event, sizeof(event)) < 0)
         exit(1);
         close(fd);
}

static void hci_send_event_packet(int fd, uint8_t evt, void* data, 
size_t data_len)
{
         struct iovec iv[3];
         struct hci_event_hdr hdr;
         hdr.evt = evt;
         hdr.plen = data_len;
         uint8_t type = HCI_EVENT_PKT;
         iv[0].iov_base = &type;
         iv[0].iov_len = sizeof(type);
         iv[1].iov_base = &hdr;
         iv[1].iov_len = sizeof(hdr);
         iv[2].iov_base = data;
         iv[2].iov_len = data_len;
         if (writev(fd, iv, sizeof(iv) / sizeof(struct iovec)) < 0)
         exit(1);
}

static void hci_send_event_cmd_complete(int fd, uint16_t opcode, void* 
data, size_t data_len)
{
         struct iovec iv[4];
         struct hci_event_hdr hdr;
         hdr.evt = HCI_EV_CMD_COMPLETE;
         hdr.plen = sizeof(struct hci_ev_cmd_complete) + data_len;
         struct hci_ev_cmd_complete evt_hdr;
         evt_hdr.ncmd = 1;
         evt_hdr.opcode = opcode;
         uint8_t type = HCI_EVENT_PKT;
         iv[0].iov_base = &type;
         iv[0].iov_len = sizeof(type);
         iv[1].iov_base = &hdr;
         iv[1].iov_len = sizeof(hdr);
         iv[2].iov_base = &evt_hdr;
         iv[2].iov_len = sizeof(evt_hdr);
         iv[3].iov_base = data;
         iv[3].iov_len = data_len;
         if (writev(fd, iv, sizeof(iv) / sizeof(struct iovec)) < 0)
         exit(1);
}

static bool process_command_pkt(int fd, char* buf, ssize_t buf_size)
{
         struct hci_command_hdr* hdr = (struct hci_command_hdr*)buf;
         if (buf_size < (ssize_t)sizeof(struct hci_command_hdr) ||
             hdr->plen != buf_size - sizeof(struct hci_command_hdr))
         exit(1);
         switch (hdr->opcode) {
         case HCI_OP_WRITE_SCAN_ENABLE: {
                 uint8_t status = 0;
                 hci_send_event_cmd_complete(fd, hdr->opcode, &status, 
sizeof(status));
                 return true;
         }
         case HCI_OP_READ_BD_ADDR: {
                 struct hci_rp_read_bd_addr rp = {0};
                 rp.status = 0;
                 memset(&rp.bdaddr, 0xaa, 6);
                 hci_send_event_cmd_complete(fd, hdr->opcode, &rp, 
sizeof(rp));
                 return false;
         }
         case HCI_OP_READ_BUFFER_SIZE: {
                 struct hci_rp_read_buffer_size rp = {0};
                 rp.status = 0;
                 rp.acl_mtu = 1021;
                 rp.sco_mtu = 96;
                 rp.acl_max_pkt = 4;
                 rp.sco_max_pkt = 6;
                 hci_send_event_cmd_complete(fd, hdr->opcode, &rp, 
sizeof(rp));
                 return false;
         }
         }
         char dummy[0xf9] = {0};
         hci_send_event_cmd_complete(fd, hdr->opcode, dummy, sizeof(dummy));
         return false;
}

static void* event_thread(void* arg)
{
         while (1) {
                 char buf[1024] = {0};
                 ssize_t buf_size = read(vhci_fd, buf, sizeof(buf));
                 if (buf_size < 0)
         exit(1);
                 if (buf_size > 0 && buf[0] == HCI_COMMAND_PKT) {
                         if (process_command_pkt(vhci_fd, buf + 1, 
buf_size - 1))
                                 break;
                 }
         }
         return NULL;
}
#define HCI_HANDLE_1 200
#define HCI_HANDLE_2 201

static void initialize_vhci()
{
         int hci_sock = socket(AF_BLUETOOTH, SOCK_RAW, BTPROTO_HCI);
         if (hci_sock < 0)
         exit(1);
         vhci_fd = open("/dev/vhci", O_RDWR);
         if (vhci_fd == -1)
         exit(1);
         const int kVhciFd = 202;
         if (dup2(vhci_fd, kVhciFd) < 0)
         exit(1);
         close(vhci_fd);
         vhci_fd = kVhciFd;
         struct vhci_vendor_pkt vendor_pkt;
         if (read(vhci_fd, &vendor_pkt, sizeof(vendor_pkt)) != 
sizeof(vendor_pkt))
         exit(1);
         if (vendor_pkt.type != HCI_VENDOR_PKT)
         exit(1);
         pthread_t th;
         if (pthread_create(&th, NULL, event_thread, NULL))
         exit(1);
         int ret = ioctl(hci_sock, HCIDEVUP, vendor_pkt.id);
         if (ret) {
                 if (errno == ERFKILL) {
                         rfkill_unblock_all();
                         ret = ioctl(hci_sock, HCIDEVUP, vendor_pkt.id);
                 }
                 if (ret && errno != EALREADY)
         exit(1);
         }
         struct hci_dev_req dr = {0};
         dr.dev_id = vendor_pkt.id;
         dr.dev_opt = SCAN_PAGE;
         if (ioctl(hci_sock, HCISETSCAN, &dr))
         exit(1);
         struct hci_ev_conn_request request;
         memset(&request, 0, sizeof(request));
         memset(&request.bdaddr, 0xaa, 6);
         *(uint8_t*)&request.bdaddr.b[5] = 0x10;
         request.link_type = ACL_LINK;
         hci_send_event_packet(vhci_fd, HCI_EV_CONN_REQUEST, &request, 
sizeof(request));
         struct hci_ev_conn_complete complete;
         memset(&complete, 0, sizeof(complete));
         complete.status = 0;
         complete.handle = HCI_HANDLE_1;
         memset(&complete.bdaddr, 0xaa, 6);
         *(uint8_t*)&complete.bdaddr.b[5] = 0x10;
         complete.link_type = ACL_LINK;
         complete.encr_mode = 0;
         hci_send_event_packet(vhci_fd, HCI_EV_CONN_COMPLETE, &complete, 
sizeof(complete));
         struct hci_ev_remote_features features;
         memset(&features, 0, sizeof(features));
         features.status = 0;
         features.handle = HCI_HANDLE_1;
         hci_send_event_packet(vhci_fd, HCI_EV_REMOTE_FEATURES, 
&features, sizeof(features));
         struct {
                 struct hci_ev_le_meta le_meta;
                 struct hci_ev_le_conn_complete le_conn;
         } le_conn;
         memset(&le_conn, 0, sizeof(le_conn));
         le_conn.le_meta.subevent = HCI_EV_LE_CONN_COMPLETE;
         memset(&le_conn.le_conn.bdaddr, 0xaa, 6);
         *(uint8_t*)&le_conn.le_conn.bdaddr.b[5] = 0x11;
         le_conn.le_conn.role = 1;
         le_conn.le_conn.handle = HCI_HANDLE_2;
         hci_send_event_packet(vhci_fd, HCI_EV_LE_META, &le_conn, 
sizeof(le_conn));
         pthread_join(th, NULL);
         close(hci_sock);
}

static long syz_emit_vhci(volatile long a0, volatile long a1)
{
         if (vhci_fd < 0)
                 return (uintptr_t)-1;
         char* data = (char*)a0;
         uint32_t length = a1;
         return write(vhci_fd, data, length);
}

static void setup_common()
{
         if (mount(0, "/sys/fs/fuse/connections", "fusectl", 0, 0)) {
         }
}

static void setup_binderfs()
{
         if (mkdir("/dev/binderfs", 0777)) {
         }
         if (mount("binder", "/dev/binderfs", "binder", 0, NULL)) {
         }
         if (symlink("/dev/binderfs", "./binderfs")) {
         }
}

static void loop();

static void sandbox_common()
{
         prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
         setsid();
         struct rlimit rlim;
         rlim.rlim_cur = rlim.rlim_max = (200 << 20);
         setrlimit(RLIMIT_AS, &rlim);
         rlim.rlim_cur = rlim.rlim_max = 32 << 20;
         setrlimit(RLIMIT_MEMLOCK, &rlim);
         rlim.rlim_cur = rlim.rlim_max = 136 << 20;
         setrlimit(RLIMIT_FSIZE, &rlim);
         rlim.rlim_cur = rlim.rlim_max = 1 << 20;
         setrlimit(RLIMIT_STACK, &rlim);
         rlim.rlim_cur = rlim.rlim_max = 0;
         setrlimit(RLIMIT_CORE, &rlim);
         rlim.rlim_cur = rlim.rlim_max = 256;
         setrlimit(RLIMIT_NOFILE, &rlim);
         if (unshare(CLONE_NEWNS)) {
         }
         if (mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL)) {
         }
         if (unshare(CLONE_NEWIPC)) {
         }
         if (unshare(0x02000000)) {
         }
         if (unshare(CLONE_NEWUTS)) {
         }
         if (unshare(CLONE_SYSVSEM)) {
         }
         typedef struct {
                 const char* name;
                 const char* value;
         } sysctl_t;
         static const sysctl_t sysctls[] = {
             {"/proc/sys/kernel/shmmax", "16777216"},
             {"/proc/sys/kernel/shmall", "536870912"},
             {"/proc/sys/kernel/shmmni", "1024"},
             {"/proc/sys/kernel/msgmax", "8192"},
             {"/proc/sys/kernel/msgmni", "1024"},
             {"/proc/sys/kernel/msgmnb", "1024"},
             {"/proc/sys/kernel/sem", "1024 1048576 500 1024"},
         };
         unsigned i;
         for (i = 0; i < sizeof(sysctls) / sizeof(sysctls[0]); i++)
                 write_file(sysctls[i].name, sysctls[i].value);
}

static int wait_for_loop(int pid)
{
         if (pid < 0)
         exit(1);
         int status = 0;
         while (waitpid(-1, &status, __WALL) != pid) {
         }
         return WEXITSTATUS(status);
}

static void drop_caps(void)
{
         struct __user_cap_header_struct cap_hdr = {};
         struct __user_cap_data_struct cap_data[2] = {};
         cap_hdr.version = _LINUX_CAPABILITY_VERSION_3;
         cap_hdr.pid = getpid();
         if (syscall(SYS_capget, &cap_hdr, &cap_data))
         exit(1);
         const int drop = (1 << CAP_SYS_PTRACE) | (1 << CAP_SYS_NICE);
         cap_data[0].effective &= ~drop;
         cap_data[0].permitted &= ~drop;
         cap_data[0].inheritable &= ~drop;
         if (syscall(SYS_capset, &cap_hdr, &cap_data))
         exit(1);
}

static int do_sandbox_none(void)
{
         if (unshare(CLONE_NEWPID)) {
         }
         int pid = fork();
         if (pid != 0)
                 return wait_for_loop(pid);
         setup_common();
         initialize_vhci();
         sandbox_common();
         drop_caps();
         if (unshare(CLONE_NEWNET)) {
         }
         setup_binderfs();
         loop();
         exit(1);
}

static void kill_and_wait(int pid, int* status)
{
         kill(-pid, SIGKILL);
         kill(pid, SIGKILL);
         for (int i = 0; i < 100; i++) {
                 if (waitpid(-1, status, WNOHANG | __WALL) == pid)
                         return;
                 usleep(1000);
         }
         DIR* dir = opendir("/sys/fs/fuse/connections");
         if (dir) {
                 for (;;) {
                         struct dirent* ent = readdir(dir);
                         if (!ent)
                                 break;
                         if (strcmp(ent->d_name, ".") == 0 || 
strcmp(ent->d_name, "..") == 0)
                                 continue;
                         char abort[300];
                         snprintf(abort, sizeof(abort), 
"/sys/fs/fuse/connections/%s/abort", ent->d_name);
                         int fd = open(abort, O_WRONLY);
                         if (fd == -1) {
                                 continue;
                         }
                         if (write(fd, abort, 1) < 0) {
                         }
                         close(fd);
                 }
                 closedir(dir);
         } else {
         }
         while (waitpid(-1, status, __WALL) != pid) {
         }
}

static void setup_test()
{
         prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
         setpgrp();
         write_file("/proc/self/oom_score_adj", "1000");
}

static void close_fds()
{
         for (int fd = 3; fd < MAX_FDS; fd++)
                 close(fd);
}

static void execute_one(void);

#define WAIT_FLAGS __WALL

static void loop(void)
{
         int iter = 0;
         for (;; iter++) {
                 int pid = fork();
                 if (pid < 0)
         exit(1);
                 if (pid == 0) {
                         setup_test();
                         execute_one();
                         close_fds();
                         exit(0);
                 }
                 int status = 0;
                 uint64_t start = current_time_ms();
                 for (;;) {
                         if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) 
== pid)
                                 break;
                         sleep_ms(1);
                         if (current_time_ms() - start < 5000)
                                 continue;
                         kill_and_wait(pid, &status);
                         break;
                 }
         }
}

void execute_one(void)
{
*(uint8_t*)0x20000040 = 4;
*(uint8_t*)0x20000041 = 8;
*(uint8_t*)0x20000042 = 4;
*(uint8_t*)0x20000043 = 0xf9;
*(uint16_t*)0x20000044 = 0xc8;
*(uint8_t*)0x20000046 = 2;
syz_emit_vhci(0x20000040, 7);

}
int main(void)
{
                 syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, 
-1, 0ul);
         syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 
0ul);
         syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
                         do_sandbox_none();
         return 0;
}

-- 
Regards,
Vasiliy Kovalev