From c9cc8d01fb04117928830449388512a5047569c9 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Wed, 31 Jan 2018 00:49:18 -0800 Subject: [PATCH] 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 #include #include #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 Cc: # v4.13+ Signed-off-by: Eric Biggers Signed-off-by: Linus Torvalds --- fs/devpts/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index 7eae33ffa3fc..e31d6ed3ec32 100644 --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -168,11 +168,11 @@ struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi) 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; }