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Date: Wed, 11 Dec 2013 09:37:24 -0500
From: "J. Bruce Fields" <bfields@...ldses.org>
To: Jeff Layton <jlayton@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
nfs-ganesha-devel@...ts.sourceforge.net,
samba-technical@...ts.samba.org
Subject: Re: [PATCH v3 1/6] locks: consolidate common code in the
flock_to_posix_lock routines
On Wed, Dec 11, 2013 at 06:18:56AM -0500, Jeff Layton wrote:
> On Tue, 10 Dec 2013 18:22:04 -0500
> "J. Bruce Fields" <bfields@...ldses.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.
Well, it'd be weird if I didn't screw up something somewhere. If we've
both looked at it and not found anything then maybe it's OK. But I'll
see if I can do some basic tests for the edge cases.
--b.
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