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    SubjectRe: [PATCH 2/5] module: Refactor section attr into bin attribute
    On Thu, Jul 02, 2020 at 04:26:35PM -0700, Kees Cook wrote:
    > In order to gain access to the open file's f_cred for kallsym visibility
    > permission checks, refactor the module section attributes to use the
    > bin_attribute instead of attribute interface. Additionally removes the
    > redundant "name" struct member.
    >
    > Cc: stable@vger.kernel.org
    > Signed-off-by: Kees Cook <keescook@chromium.org>
    > ---
    > kernel/module.c | 45 ++++++++++++++++++++++++---------------------
    > 1 file changed, 24 insertions(+), 21 deletions(-)
    >
    > diff --git a/kernel/module.c b/kernel/module.c
    > index a5022ae84e50..9e2954519259 100644
    > --- a/kernel/module.c
    > +++ b/kernel/module.c
    > @@ -1510,8 +1510,7 @@ static inline bool sect_empty(const Elf_Shdr *sect)
    > }
    >
    > struct module_sect_attr {
    > - struct module_attribute mattr;
    > - char *name;
    > + struct bin_attribute battr;
    > unsigned long address;
    > };
    >
    > @@ -1521,11 +1520,16 @@ struct module_sect_attrs {
    > struct module_sect_attr attrs[];
    > };
    >
    > -static ssize_t module_sect_show(struct module_attribute *mattr,
    > - struct module_kobject *mk, char *buf)
    > +static ssize_t module_sect_read(struct file *file, struct kobject *kobj,
    > + struct bin_attribute *battr,
    > + char *buf, loff_t pos, size_t count)
    > {
    > struct module_sect_attr *sattr =
    > - container_of(mattr, struct module_sect_attr, mattr);
    > + container_of(battr, struct module_sect_attr, battr);
    > +
    > + if (pos != 0)
    > + return -EINVAL;
    > +
    > return sprintf(buf, "0x%px\n", kptr_restrict < 2 ?
    > (void *)sattr->address : NULL);
    > }
    > @@ -1535,7 +1539,7 @@ static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
    > unsigned int section;
    >
    > for (section = 0; section < sect_attrs->nsections; section++)
    > - kfree(sect_attrs->attrs[section].name);
    > + kfree(sect_attrs->attrs[section].battr.attr.name);
    > kfree(sect_attrs);
    > }
    >
    > @@ -1544,42 +1548,41 @@ static void add_sect_attrs(struct module *mod, const struct load_info *info)
    > unsigned int nloaded = 0, i, size[2];
    > struct module_sect_attrs *sect_attrs;
    > struct module_sect_attr *sattr;
    > - struct attribute **gattr;
    > + struct bin_attribute **gattr;
    >
    > /* Count loaded sections and allocate structures */
    > for (i = 0; i < info->hdr->e_shnum; i++)
    > if (!sect_empty(&info->sechdrs[i]))
    > nloaded++;
    > size[0] = ALIGN(struct_size(sect_attrs, attrs, nloaded),
    > - sizeof(sect_attrs->grp.attrs[0]));
    > - size[1] = (nloaded + 1) * sizeof(sect_attrs->grp.attrs[0]);
    > + sizeof(sect_attrs->grp.bin_attrs[0]));
    > + size[1] = (nloaded + 1) * sizeof(sect_attrs->grp.bin_attrs[0]);
    > sect_attrs = kzalloc(size[0] + size[1], GFP_KERNEL);
    > if (sect_attrs == NULL)
    > return;
    >
    > /* Setup section attributes. */
    > sect_attrs->grp.name = "sections";
    > - sect_attrs->grp.attrs = (void *)sect_attrs + size[0];
    > + sect_attrs->grp.bin_attrs = (void *)sect_attrs + size[0];
    >
    > sect_attrs->nsections = 0;
    > sattr = &sect_attrs->attrs[0];
    > - gattr = &sect_attrs->grp.attrs[0];
    > + gattr = &sect_attrs->grp.bin_attrs[0];
    > for (i = 0; i < info->hdr->e_shnum; i++) {
    > Elf_Shdr *sec = &info->sechdrs[i];
    > if (sect_empty(sec))
    > continue;
    > + sysfs_bin_attr_init(&sattr->battr);
    > sattr->address = sec->sh_addr;
    > - sattr->name = kstrdup(info->secstrings + sec->sh_name,
    > - GFP_KERNEL);
    > - if (sattr->name == NULL)
    > + sattr->battr.attr.name =
    > + kstrdup(info->secstrings + sec->sh_name, GFP_KERNEL);
    > + if (sattr->battr.attr.name == NULL)
    > goto out;
    > sect_attrs->nsections++;
    > - sysfs_attr_init(&sattr->mattr.attr);
    > - sattr->mattr.show = module_sect_show;
    > - sattr->mattr.store = NULL;
    > - sattr->mattr.attr.name = sattr->name;
    > - sattr->mattr.attr.mode = S_IRUSR;
    > - *(gattr++) = &(sattr++)->mattr.attr;
    > + sattr->battr.read = module_sect_read;
    > + sattr->battr.size = 3 /* "0x", "\n" */ + (BITS_PER_LONG / 4);
    > + sattr->battr.attr.mode = 0400;
    > + *(gattr++) = &(sattr++)->battr;
    > }
    > *gattr = NULL;
    >
    > @@ -1669,7 +1672,7 @@ static void add_notes_attrs(struct module *mod, const struct load_info *info)
    > continue;
    > if (info->sechdrs[i].sh_type == SHT_NOTE) {
    > sysfs_bin_attr_init(nattr);
    > - nattr->attr.name = mod->sect_attrs->attrs[loaded].name;
    > + nattr->attr.name = mod->sect_attrs->attrs[loaded].battr.attr.name;
    > nattr->attr.mode = S_IRUGO;
    > nattr->size = info->sechdrs[i].sh_size;
    > nattr->private = (void *) info->sechdrs[i].sh_addr;
    > --
    > 2.25.1
    >

    They get a correct "size" value now, nice!

    Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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