| Message ID | 20200702232638.2946421-3-keescook@chromium.org |
|---|---|
| State | Not Applicable |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | Refactor kallsyms_show_value() users for correct cred | expand |
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 = §_attrs->attrs[0]; > - gattr = §_attrs->grp.attrs[0]; > + gattr = §_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>
On Fri, Jul 03, 2020 at 08:02:07AM +0200, Greg Kroah-Hartman wrote: > On Thu, Jul 02, 2020 at 04:26:35PM -0700, Kees Cook wrote: > > + sattr->battr.size = 3 /* "0x", "\n" */ + (BITS_PER_LONG / 4); > > They get a correct "size" value now, nice! Yeah, though I do have some concerns that switching to a bin attribute changes the userspace behavior a bit. With seq_file-based "show", we get a 4096 size, and seeking isn't possible (lseek to non-0 location will fail). With the raw "read", we get the right size, but lseek() is allowed (but I've got the "read" handler refuse reads starting from non-zero). When I reviewed[1] potential readers (elftutils, systemtap, kmod), they all seem to do normal things (fopen/fscanf/fclose), so I'm hoping this won't be a problem in practice. > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Thanks! [1] https://codesearch.debian.net/search?q=%2Fsys%2Fmodule.*sections&literal=0
+++ Kees Cook [02/07/20 16:26 -0700]: >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> Hi Kees, This looks good to me: Tested-by: Jessica Yu <jeyu@kernel.org> Acked-by: Jessica Yu <jeyu@kernel.org> Thanks!
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 = §_attrs->attrs[0]; - gattr = §_attrs->grp.attrs[0]; + gattr = §_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;
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(-)