On Fri, 13 Oct 2017, Al Viro wrote:
> On Fri, Oct 13, 2017 at 01:39:13PM -0400, Nicolas Pitre wrote:
> > On Fri, 13 Oct 2017, Al Viro wrote:
> >
> > > On Thu, Oct 12, 2017 at 02:16:10AM -0400, Nicolas Pitre wrote:
> > >
> > > > static void cramfs_kill_sb(struct super_block *sb)
> > > > {
> > > > struct cramfs_sb_info *sbi = CRAMFS_SB(sb);
> > > >
> > > > - kill_block_super(sb);
> > > > + if (IS_ENABLED(CCONFIG_CRAMFS_MTD)) {
> > > > + if (sbi->mtd_point_size)
> > > > + mtd_unpoint(sb->s_mtd, 0, sbi->mtd_point_size);
> > > > + if (sb->s_mtd)
> > > > + kill_mtd_super(sb);
> > >
> > > ...
> > >
> > > > + mtd_unpoint(sb->s_mtd, 0, PAGE_SIZE);
> > > > + err = mtd_point(sb->s_mtd, 0, sbi->size, &sbi->mtd_point_size,
> > > > + &sbi->linear_virt_addr, &sbi->linear_phys_addr);
> > > > + if (err || sbi->mtd_point_size != sbi->size) {
> > >
> > > What happens if that mtd_point() fails? Note that ->kill_sb() will be
> > > called anyway and ->mtd_point_size is going to be non-zero here...
> >
> > mtd_point() always clears sbi->mtd_point_size first thing upon entry
> > even before it has a chance to fail. So it it fails then
> > sbi->mtd_point_size will be zero and ->kill_sb() will skip the unpoint
> > call.
>
> OK... I wonder if it should simply define stubs for kill_mtd_super(),
> mtd_unpoint() and kill_block_super() in !CONFIG_MTD and !CONFIG_BLOCK
> cases. mount_mtd() and mount_bdev() as well - e.g. mount_bdev()
> returning ERR_PTR(-ENODEV) and kill_block_super() being simply BUG()
> in !CONFIG_BLOCK case. Then cramfs_kill_sb() would be
> if (sb->s_mtd) {
> if (sbi->mtd_point_size)
> mtd_unpoint(sb->s_mtd, 0, sbi->mtd_point_size);
> kill_mtd_super(sb);
> } else {
> kill_block_super(sb);
> }
> kfree(sbi);
What I really like about IS_ENABLED() usage is the immediate build
coverage without having to run all config combinations. The compiler
will discard unneeded code and avoid pesky unused variable warnings that
require ugly #ifdefs otherwise.
> Wait. Looking at that code... what happens if you hit this failure
> exit:
> sbi = kzalloc(sizeof(struct cramfs_sb_info), GFP_KERNEL);
> if (!sbi)
> return -ENOMEM;
>
> Current cramfs_kill_sb() will do kill_block_super() and kfree(NULL), which
> works nicely, but you are dereferencing that sucker, not just passing it
> to kfree(). IOW, that if (sbi->....) ought to be if (sbi && sbi->...)
Right, good catch.
Fixed in my tree now.
Nicolas
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