4.15-stable review patch. If anyone has any objections, please let me know.
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From: Eric Biggers ebiggers@google.com
commit c9cc8d01fb04117928830449388512a5047569c9 upstream.
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: 311fc65c9fb9 ("pty: Repair TIOCGPTPEER") Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: Eric Biggers ebiggers@google.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/devpts/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -168,11 +168,11 @@ struct vfsmount *devpts_mntget(struct fi dput(path.dentry); if (err) { mntput(path.mnt); - path.mnt = ERR_PTR(err); + return ERR_PTR(err); } if (DEVPTS_SB(path.mnt->mnt_sb) != fsi) { mntput(path.mnt); - path.mnt = ERR_PTR(-ENODEV); + return ERR_PTR(-ENODEV); } return path.mnt; }