Re: [RFC PATCH] fs/lock: increase the filp's reference for Posix-style locks

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-11-07 at 17:52 +0800, xiubli@redhat.com wrote:
> From: Xiubo Li <xiubli@redhat.com>
> 
> When closing the file descripters in parallel in multiple threads,
> who are sharing the same file descripters, the filp_close() will
> remove all the Posix-style locks. But if two threads both calling
> the filp_close() it may race and cause use-after-free crash:
> 
>  PID: 327771   TASK: ffff952aa1db3180  CPU: 8    COMMAND: "db2fmp"
>   #0 [ffff95202f33b960] machine_kexec at ffffffff890662f4
>   #1 [ffff95202f33b9c0] __crash_kexec at ffffffff89122b82
>   #2 [ffff95202f33ba90] crash_kexec at ffffffff89122c70
>   #3 [ffff95202f33baa8] oops_end at ffffffff89791798
>   #4 [ffff95202f33bad0] no_context at ffffffff89075d14
>   #5 [ffff95202f33bb20] __bad_area_nosemaphore at ffffffff89075fe2
>   #6 [ffff95202f33bb70] bad_area_nosemaphore at ffffffff89076104
>   #7 [ffff95202f33bb80] __do_page_fault at ffffffff89794750
>   #8 [ffff95202f33bbf0] do_page_fault at ffffffff89794975
>   #9 [ffff95202f33bc20] page_fault at ffffffff89790778
>      [exception RIP: ceph_fl_release_lock+20]
>      RIP: ffffffffc08247a4  RSP: ffff95202f33bcd0  RFLAGS: 00010286
>      RAX: ffff952d4ebd8a00  RBX: 0000000000000000  RCX: dead000000000200
>      RDX: ffff95202f33bd60  RSI: ffff95202f33bd60  RDI: ffff9526b6ac5b00
>      RBP: ffff95202f33bce0   R8: ffff9526b6ac5b18   R9: ffffffffc083c368
>      R10: 0000000000001109  R11: 0000000000000000  R12: ffff95202f33bd60
>      R13: ffff9526b6ac5b00  R14: 0000000000000000  R15: 0000000000000000
>      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
>  #10 [ffff95202f33bce8] locks_release_private at ffffffff892ab3d7
>  #11 [ffff95202f33bd00] locks_free_lock at ffffffff892ac34d
>  #12 [ffff95202f33bd18] locks_dispose_list at ffffffff892ac44b
>  #13 [ffff95202f33bd40] __posix_lock_file at ffffffff892acdfa
>  #14 [ffff95202f33bda8] posix_lock_file at ffffffff892ad146
>  #15 [ffff95202f33bdb8] ceph_lock at ffffffffc0824e8a [ceph]
>  #16 [ffff95202f33bdf8] vfs_lock_file at ffffffff892ad185
>  #17 [ffff95202f33be08] locks_remove_posix at ffffffff892ad239
>  #18 [ffff95202f33bee0] locks_remove_posix at ffffffff892ad2a0
>  #19 [ffff95202f33bef0] filp_close at ffffffff8924baa6
>  #20 [ffff95202f33bf18] __close_fd at ffffffff8926f89c
>  #21 [ffff95202f33bf40] sys_close at ffffffff8924d503
>  #22 [ffff95202f33bf50] system_call_fastpath at ffffffff89799f92
>      RIP: 00007f806ec446ab  RSP: 00007f80517f0d90  RFLAGS: 00010206
>      RAX: 0000000000000003  RBX: 00007f8030001a20  RCX: 00007f80300386b0
>      RDX: 00007f806ef0d880  RSI: 0000000000000001  RDI: 0000000000000006
>      RBP: 00007f806ef0e3c0   R8: 00007f80517fa700   R9: 0000000000000000
>      R10: 0000000000000000  R11: 0000000000000206  R12: 0000000000000000
>      R13: 00007f80300035b0  R14: 00007f80517f1104  R15: 000000000000006c
>      ORIG_RAX: 0000000000000003  CS: 0033  SS: 002b
> 
> We need to make sure that the filp in the file_lock shouldn't be
> release when any file_lock is still referring to it.
> 
> For the Posix-style locks, whose owner will be the thread ids, we
> will increase the filp's reference.
> 
> URL: https://tracker.ceph.com/issues/57986
> Signed-off-by: Xiubo Li <xiubli@redhat.com>
> ---
>  drivers/android/binder.c |  2 +-
>  fs/file.c                | 15 ++++++++++-----
>  fs/locks.c               | 18 +++++++++++++++---
>  include/linux/fs.h       | 14 ++++++++++++++
>  io_uring/openclose.c     |  3 ++-
>  5 files changed, 42 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 880224ec6abb..03692564d940 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1924,7 +1924,7 @@ static void binder_deferred_fd_close(int fd)
>  	if (twcb->file) {
>  		// pin it until binder_do_fd_close(); see comments there
>  		get_file(twcb->file);
> -		filp_close(twcb->file, current->files);
> +		filp_close(twcb->file, file_lock_make_thread_owner(current->files));
>  		task_work_add(current, &twcb->twork, TWA_RESUME);
>  	} else {
>  		kfree(twcb);
> diff --git a/fs/file.c b/fs/file.c
> index 5f9c802a5d8d..39ad8e74a8d9 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -417,6 +417,7 @@ static struct fdtable *close_files(struct files_struct * files)
>  	 * files structure.
>  	 */
>  	struct fdtable *fdt = rcu_dereference_raw(files->fdt);
> +	fl_owner_t owner = file_lock_make_thread_owner(files);
>  	unsigned int i, j = 0;
>  
>  	for (;;) {
> @@ -429,7 +430,7 @@ static struct fdtable *close_files(struct files_struct * files)
>  			if (set & 1) {
>  				struct file * file = xchg(&fdt->fd[i], NULL);
>  				if (file) {
> -					filp_close(file, files);
> +					filp_close(file, owner);
>  					cond_resched();
>  				}
>  			}
> @@ -653,6 +654,7 @@ static struct file *pick_file(struct files_struct *files, unsigned fd)
>  int close_fd(unsigned fd)
>  {
>  	struct files_struct *files = current->files;
> +	fl_owner_t owner = file_lock_make_thread_owner(files);
>  	struct file *file;
>  
>  	spin_lock(&files->file_lock);
> @@ -661,7 +663,7 @@ int close_fd(unsigned fd)
>  	if (!file)
>  		return -EBADF;
>  
> -	return filp_close(file, files);
> +	return filp_close(file, owner);
>  }
>  EXPORT_SYMBOL(close_fd); /* for ksys_close() */
>  
> @@ -695,6 +697,7 @@ static inline void __range_cloexec(struct files_struct *cur_fds,
>  static inline void __range_close(struct files_struct *cur_fds, unsigned int fd,
>  				 unsigned int max_fd)
>  {
> +	fl_owner_t owner = file_lock_make_thread_owner(cur_fds);
>  	unsigned n;
>  
>  	rcu_read_lock();
> @@ -711,7 +714,7 @@ static inline void __range_close(struct files_struct *cur_fds, unsigned int fd,
>  
>  		if (file) {
>  			/* found a valid file to close */
> -			filp_close(file, cur_fds);
> +			filp_close(file, owner);
>  			cond_resched();
>  		}
>  	}
> @@ -816,6 +819,7 @@ struct file *close_fd_get_file(unsigned int fd)
>  
>  void do_close_on_exec(struct files_struct *files)
>  {
> +	fl_owner_t owner = file_lock_make_thread_owner(files);
>  	unsigned i;
>  	struct fdtable *fdt;
>  
> @@ -841,7 +845,7 @@ void do_close_on_exec(struct files_struct *files)
>  			rcu_assign_pointer(fdt->fd[fd], NULL);
>  			__put_unused_fd(files, fd);
>  			spin_unlock(&files->file_lock);
> -			filp_close(file, files);
> +			filp_close(file, owner);
>  			cond_resched();
>  			spin_lock(&files->file_lock);
>  		}
> @@ -1080,6 +1084,7 @@ static int do_dup2(struct files_struct *files,
>  	struct file *file, unsigned fd, unsigned flags)
>  __releases(&files->file_lock)
>  {
> +	fl_owner_t owner = file_lock_make_thread_owner(files);
>  	struct file *tofree;
>  	struct fdtable *fdt;
>  
> @@ -1111,7 +1116,7 @@ __releases(&files->file_lock)
>  	spin_unlock(&files->file_lock);
>  
>  	if (tofree)
> -		filp_close(tofree, files);
> +		filp_close(tofree, owner);
>  
>  	return fd;
>  
> diff --git a/fs/locks.c b/fs/locks.c
> index 607f94a0e789..e8b67f87e0ee 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -331,6 +331,8 @@ EXPORT_SYMBOL_GPL(locks_owner_has_blockers);
>  /* Free a lock which is not in use. */
>  void locks_free_lock(struct file_lock *fl)
>  {
> +	if (fl->fl_file && file_lock_is_thread_owner(fl->fl_owner))
> +		fput(fl->fl_file);
>  	locks_release_private(fl);
>  	kmem_cache_free(filelock_cache, fl);
>  }
> @@ -384,7 +386,10 @@ void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
>  
>  	locks_copy_conflock(new, fl);
>  
> -	new->fl_file = fl->fl_file;
> +	if (file_lock_is_thread_owner(new->fl_owner))
> +		new->fl_file = get_file(fl->fl_file);
> +	else
> +		new->fl_file = fl->fl_file;
>  	new->fl_ops = fl->fl_ops;
>  
>  	if (fl->fl_ops) {
> @@ -488,13 +493,14 @@ static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
>  	} else
>  		fl->fl_end = OFFSET_MAX;
>  
> -	fl->fl_owner = current->files;
> +	fl->fl_owner = file_lock_make_thread_owner(current->files);
>  	fl->fl_pid = current->tgid;
> -	fl->fl_file = filp;
> +	fl->fl_file = get_file(filp);
>  	fl->fl_flags = FL_POSIX;
>  	fl->fl_ops = NULL;
>  	fl->fl_lmops = NULL;
>  
> +
>  	return assign_type(fl, l->l_type);
>  }
>  
> @@ -2243,6 +2249,7 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
>  
>  		fl->fl_flags |= FL_OFDLCK;
>  		fl->fl_owner = filp;
> +		fput(filp);
>  	}
>  
>  	error = vfs_test_lock(filp, fl);
> @@ -2376,6 +2383,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
>  		cmd = F_SETLK;
>  		file_lock->fl_flags |= FL_OFDLCK;
>  		file_lock->fl_owner = filp;
> +		fput(filp);
>  		break;
>  	case F_OFD_SETLKW:
>  		error = -EINVAL;
> @@ -2385,6 +2393,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
>  		cmd = F_SETLKW;
>  		file_lock->fl_flags |= FL_OFDLCK;
>  		file_lock->fl_owner = filp;
> +		fput(filp);
>  		fallthrough;
>  	case F_SETLKW:
>  		file_lock->fl_flags |= FL_SLEEP;
> @@ -2450,6 +2459,7 @@ int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 *flock)
>  		cmd = F_GETLK64;
>  		fl->fl_flags |= FL_OFDLCK;
>  		fl->fl_owner = filp;
> +		fput(filp);
>  	}
>  
>  	error = vfs_test_lock(filp, fl);
> @@ -2499,6 +2509,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>  		cmd = F_SETLK64;
>  		file_lock->fl_flags |= FL_OFDLCK;
>  		file_lock->fl_owner = filp;
> +		fput(filp);
>  		break;
>  	case F_OFD_SETLKW:
>  		error = -EINVAL;
> @@ -2508,6 +2519,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>  		cmd = F_SETLKW64;
>  		file_lock->fl_flags |= FL_OFDLCK;
>  		file_lock->fl_owner = filp;
> +		fput(filp);
>  		fallthrough;
>  	case F_SETLKW64:
>  		file_lock->fl_flags |= FL_SLEEP;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e654435f1651..d7d81962a863 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1028,6 +1028,20 @@ static inline struct file *get_file(struct file *f)
>  /* legacy typedef, should eventually be removed */
>  typedef void *fl_owner_t;
>  
> +/*
> + * Set the last significant bit to 1 to mark that
> + * we have get a reference of the fl->fl_file.
> + */
> +static inline fl_owner_t file_lock_make_thread_owner(fl_owner_t owner)
> +{
> +	return (fl_owner_t)((unsigned long)owner | 1UL);
> +}
> +
> +static inline bool file_lock_is_thread_owner(fl_owner_t owner)
> +{
> +	return ((unsigned long)owner & 1UL);
> +}
> +
>  struct file_lock;
>  
>  struct file_lock_operations {
> diff --git a/io_uring/openclose.c b/io_uring/openclose.c
> index 67178e4bb282..5a12cdf7f8d0 100644
> --- a/io_uring/openclose.c
> +++ b/io_uring/openclose.c
> @@ -212,6 +212,7 @@ int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>  int io_close(struct io_kiocb *req, unsigned int issue_flags)
>  {
>  	struct files_struct *files = current->files;
> +	fl_owner_t owner = file_lock_make_thread_owner(files);
>  	struct io_close *close = io_kiocb_to_cmd(req, struct io_close);
>  	struct fdtable *fdt;
>  	struct file *file;
> @@ -247,7 +248,7 @@ int io_close(struct io_kiocb *req, unsigned int issue_flags)
>  		goto err;
>  
>  	/* No ->flush() or already async, safely close from here */
> -	ret = filp_close(file, current->files);
> +	ret = filp_close(file, owner);
>  err:
>  	if (ret < 0)
>  		req_set_fail(req);

I think this is the wrong approach to fixing this. It also looks like
you could hit a similar problem with OFD locks and this patch wouldn't
address that issue.

The real bug seems to be that ceph_fl_release_lock dereferences fl_file,
at a point when it shouldn't rely on that being valid. Most filesystems
stash some info in fl->fl_u if they need to do bookkeeping after
releasing a lock. Perhaps ceph should be doing something similar?
-- 
Jeff Layton <jlayton@kernel.org>