[PATCH v3 1/6] locks: consolidate common code in the flock_to_posix_lock routines

[Jeff Layton]

On Tue, 10 Dec 2013 18:22:04 -0500
"J. Bruce Fields" <bfields at fieldses.org> wrote:

> On Tue, Dec 10, 2013 at 04:22:53PM -0500, bfields wrote:
> > On Tue, Dec 10, 2013 at 02:17:30PM -0500, Jeff Layton wrote:
> > > Currently, there's a lot of copy and paste between the two.  Add some
> > > functions to do the initialization of the file_lock from values
> > > passed in, and turn the flock/flock64 variants of those functions into
> > > wrappers around them.
> > > 
> > > Unfortunately it's harder to consolidate the fl_start/fl_end
> > > calculations due to the differently sized types involved so I've left
> > > them separate for now.
> > 
> > I'd think you could assign everything to the flock64 type and do the
> > common work there or something.
> > 
> > But I'm confused about what the current code is actually trying to do:
> > if I'm chasing down the definitions right, these quantities are all
> > signed, and when start is defined as an off_t it can overflow in the
> > SEEK_CUR and SEEK_END cases.  And
> > 
> > 	if (fl->fl_end < fl->fl_start)
> > 		return -EOVERFLOW
> > 
> > is counting on overlow wrapping around, which I thought wasn't
> > guaranteed in the case of signed arithmetic?
> 
> E.g. the following (untested) removes the duplication and should return
> -EOVERFLOW in the cases we currently do a random conversion from 64- to
> 32-bit and back.  Susv3 says:
> 
> 	[EOVERFLOW]
> 	The cmd argument is F_GETLK, F_SETLK, or F_SETLKW and the
> 	smallest or, if l_len is non-zero, the largest offset of any
> 	byte in the requested segment cannot be represented correctly in
> 	an object of type off_t.
> 
> so that's what I tried to do.
> 
> --b.
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 92a0f0a..47832f5 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -344,48 +344,41 @@ static int assign_type(struct file_lock *fl, long type)
>  	return 0;
>  }
>  
> -/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
> - * style lock.
> - */
> -static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
> -			       struct flock *l)
> +static int flock_to_posix_lock_common(struct file *filp, struct file_lock *fl,
> +					struct flock64 *l, loff_t offset_max)
>  {
> -	off_t start, end;
> +	loff_t start;
>  
>  	switch (l->l_whence) {
>  	case SEEK_SET:
> -		start = 0;
> -		break;
> +		fl->fl_start = 0;
>  	case SEEK_CUR:
> -		start = filp->f_pos;
> -		break;
> +		fl->fl_start = filp->f_pos;
>  	case SEEK_END:
> -		start = i_size_read(file_inode(filp));
> -		break;
> +		fl->fl_start = i_size_read(file_inode(filp));
>  	default:
>  		return -EINVAL;
>  	}
> +	if (l->l_start < 0)
> +		return -EINVAL;
> +	if (l->l_start > offset_max - fl->fl_start)
> +		return -EOVERFLOW;
> +	fl->fl_start += l->l_start;
> +	if (l->l_len > offset_max - fl->fl_start)
> +		return -EOVERFLOW;
> +	if (fl->fl_start + l->l_len < 0)
> +		return -EINVAL;
>  
>  	/* POSIX-1996 leaves the case l->l_len < 0 undefined;
>  	   POSIX-2001 defines it. */
> -	start += l->l_start;
> -	if (start < 0)
> -		return -EINVAL;
> -	fl->fl_end = OFFSET_MAX;
> -	if (l->l_len > 0) {
> -		end = start + l->l_len - 1;
> -		fl->fl_end = end;
> -	} else if (l->l_len < 0) {
> -		end = start - 1;
> -		fl->fl_end = end;
> -		start += l->l_len;
> -		if (start < 0)
> -			return -EINVAL;
> -	}
> -	fl->fl_start = start;	/* we record the absolute position */
> -	if (fl->fl_end < fl->fl_start)
> -		return -EOVERFLOW;
> -	
> +	if (l->l_len > 0)
> +		fl->fl_end = fl->fl_start + l->l_len - 1;
> +	else if (l->l_len < 0) {
> +		fl->fl_end = start - 1;
> +		fl->fl_start += l->l_len;
> +	} else
> +		fl->fl_end = OFFSET_MAX;
> +
>  	fl->fl_owner = current->files;
>  	fl->fl_pid = current->tgid;
>  	fl->fl_file = filp;
> @@ -396,50 +389,27 @@ static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
>  	return assign_type(fl, l->l_type);
>  }
>  
> +/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
> + * style lock.
> + */
> +static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
> +			       struct flock *l)
> +{
> +	struct flock64 ll = {
> +		.l_type = l->l_type,
> +		.l_whence = l->l_whence,
> +		.l_start = l->l_start,
> +		.l_len = l->l_len,
> +	};
> +	
> +	return flock_to_posix_lock_common(filp, fl, &ll, OFFT_OFFSET_MAX);
> +}
> +
>  #if BITS_PER_LONG == 32
>  static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
>  				 struct flock64 *l)
>  {
> -	loff_t start;
> -
> -	switch (l->l_whence) {
> -	case SEEK_SET:
> -		start = 0;
> -		break;
> -	case SEEK_CUR:
> -		start = filp->f_pos;
> -		break;
> -	case SEEK_END:
> -		start = i_size_read(file_inode(filp));
> -		break;
> -	default:
> -		return -EINVAL;
> -	}
> -
> -	start += l->l_start;
> -	if (start < 0)
> -		return -EINVAL;
> -	fl->fl_end = OFFSET_MAX;
> -	if (l->l_len > 0) {
> -		fl->fl_end = start + l->l_len - 1;
> -	} else if (l->l_len < 0) {
> -		fl->fl_end = start - 1;
> -		start += l->l_len;
> -		if (start < 0)
> -			return -EINVAL;
> -	}
> -	fl->fl_start = start;	/* we record the absolute position */
> -	if (fl->fl_end < fl->fl_start)
> -		return -EOVERFLOW;
> -	
> -	fl->fl_owner = current->files;
> -	fl->fl_pid = current->tgid;
> -	fl->fl_file = filp;
> -	fl->fl_flags = FL_POSIX;
> -	fl->fl_ops = NULL;
> -	fl->fl_lmops = NULL;
> -
> -	return assign_type(fl, l->l_type);
> +	return flock_to_posix_lock_common(filp, fl, l, OFFSET_MAX);
>  }
>  #endif
>  
> diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
> index 95e46c8..36025f7 100644
> --- a/include/uapi/asm-generic/fcntl.h
> +++ b/include/uapi/asm-generic/fcntl.h
> @@ -186,8 +186,6 @@ struct flock {
>  };
>  #endif
>  
> -#ifndef CONFIG_64BIT
> -
>  #ifndef HAVE_ARCH_STRUCT_FLOCK64
>  #ifndef __ARCH_FLOCK64_PAD
>  #define __ARCH_FLOCK64_PAD
> @@ -202,6 +200,5 @@ struct flock64 {
>  	__ARCH_FLOCK64_PAD
>  };
>  #endif
> -#endif /* !CONFIG_64BIT */
>  
>  #endif /* _ASM_GENERIC_FCNTL_H */

Nice. I had started to consolidate them, but then figured out that
there are so many edge cases and I didn't have a good way to test them
all.

As far as I can tell though, this looks correct. I'll plan to drop my
patch and base the rest of the set on top of yours.

Thanks,
-- 
Jeff Layton <jlayton at redhat.com>