Re: Subject: [PATCH 02/16] Squashfs: directory lookup operations

[Michael Tokarev]

Geert Uytterhoeven wrote:
> On Fri, 17 Oct 2008, Phillip Lougher wrote:
> > --- /dev/null
> > +++ b/fs/squashfs/namei.c
>
> > +static int get_dir_index_using_name(struct super_block *s,
> > +			long long *next_block, unsigned int *next_offset,
> > +			long long index_start, unsigned int index_offset,
> > +			int i_count, const char *name, int len)
> > +{
> > +	struct squashfs_sb_info *msblk = s->s_fs_info;
> > +	int i, size, length = 0;
> > +	struct squashfs_dir_index *index;
> > +	char *str;
> > +
> > +	TRACE("Entered get_dir_index_using_name, i_count %d\n", i_count);
> > +
> > +	str = kmalloc(sizeof(*index) + (SQUASHFS_NAME_LEN + 1) * 2, GFP_KERNEL);
> > +	if (str == NULL) {
> > +		ERROR("Failed to allocate squashfs_dir_index\n");
> > +		goto out;
> > +	}
> > +
> > +	index = (struct squashfs_dir_index *) (str + SQUASHFS_NAME_LEN + 1);
>
> As str has been returned by kmalloc(), and SQUASHFS_NAME_LEN is equal to 256,
> `str + SQUASHFS_NAME_LEN + 1` is an odd address.
[..]
> > +		size = le32_to_cpu(index->size) + 1;
>                                    ^^^^^^^^^^^
[.]
> Hence accessing multi-byte fields in struct squashfs_dir_index causes unaligned
> accesses, which are emulated on some architectures (e.g. on MIPS).
>
> Use get_unaligned_le32() for unaligned accesses.

How about aligning it properly in the first place instead?
Three ways:

  1) reordering index and str here, so that index comes first,
     str next.

  2) using another constant instead of +1

  3) using separate allocations for separate objects.

/mjt
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