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Refactor kallsyms_show_value() users for correct cred

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Several users of kallsyms_show_value() were performing checks not
 during "open". Refactor everything needed to gain proper checks against
 file->f_cred for modules, kprobes, and bpf.
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Merge tag 'kallsyms_show_value-v5.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull kallsyms fix from Kees Cook:
 "Refactor kallsyms_show_value() users for correct cred.

  I'm not delighted by the timing of getting these changes to you, but
  it does fix a handful of kernel address exposures, and no one has
  screamed yet at the patches.

  Several users of kallsyms_show_value() were performing checks not
  during "open". Refactor everything needed to gain proper checks
  against file->f_cred for modules, kprobes, and bpf"

* tag 'kallsyms_show_value-v5.8-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  selftests: kmod: Add module address visibility test
  bpf: Check correct cred for CAP_SYSLOG in bpf_dump_raw_ok()
  kprobes: Do not expose probe addresses to non-CAP_SYSLOG
  module: Do not expose section addresses to non-CAP_SYSLOG
  module: Refactor section attr into bin attribute
  kallsyms: Refactor kallsyms_show_value() to take cred
This commit is contained in:
Linus Torvalds 2020-07-09 13:09:30 -07:00
commit ce69fb3b39
8 changed files with 103 additions and 53 deletions
Download patch file Download diff file Expand all files Collapse all files

51
kernel/module.c
View file

@ -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;
};
@ -1521,13 +1520,18 @@ 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);
return sprintf(buf, "0x%px\n", kptr_restrict < 2 ?
(void *)sattr->address : NULL);
container_of(battr, struct module_sect_attr, battr);
if (pos != 0)
return -EINVAL;
return sprintf(buf, "0x%px\n",
kallsyms_show_value(file->f_cred) ? (void *)sattr->address : NULL);
}
static void free_sect_attrs(struct module_sect_attrs *sect_attrs)
@ -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;
@ -4379,7 +4382,7 @@ static int modules_open(struct inode *inode, struct file *file)
if (!err) {
struct seq_file *m = file->private_data;
m->private = kallsyms_show_value() ? NULL : (void *)8ul;
m->private = kallsyms_show_value(file->f_cred) ? NULL : (void *)8ul;
}
return err;