devpts: fix error handling in devpts_mntget()
If devpts_ptmx_path() returns an error code, then devpts_mntget()
dereferences an ERR_PTR():
BUG: unable to handle kernel paging request at fffffffffffffff5
IP: devpts_mntget+0x13f/0x280 fs/devpts/inode.c:173
Fix it by returning early in the error paths.
Reproducer:
#define _GNU_SOURCE
#include <fcntl.h>
#include <sched.h>
#include <sys/ioctl.h>
#define TIOCGPTPEER _IO('T', 0x41)
int main()
{
for (;;) {
int fd = open("/dev/ptmx", 0);
unshare(CLONE_NEWNS);
ioctl(fd, TIOCGPTPEER, 0);
}
}
Fixes: 311fc65c9f ("pty: Repair TIOCGPTPEER")
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: <stable@vger.kernel.org> # v4.13+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
c9cc8d01fb