[PATCH 2/5] module: Refactor section attr into bin attribute

Kees Cook
2020-07-02T23:26:44Z

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