[PATCH 1/2] module: add syscall to load module from fd
From: Kees Cook
Date: Fri Sep 07 2012 - 14:38:59 EST
Instead of (or in addition to) kernel module signing, being able to reason
about the origin of a kernel module would be valuable in situations
where an OS already trusts a specific file system, file, etc, due to
things like security labels or an existing root of trust to a partition
through things like dm-verity.
This introduces a new syscall (currently only on x86), similar to
init_module, that has only two arguments. The first argument is used as
a file descriptor to the module and the second argument is a pointer to
the NULL terminated string of module arguments.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
v2:
- various cleanups, thanks to Rusty Russell.
---
arch/x86/syscalls/syscall_32.tbl | 1 +
arch/x86/syscalls/syscall_64.tbl | 1 +
include/linux/syscalls.h | 1 +
kernel/module.c | 214 ++++++++++++++++++++++++++-----------
kernel/sys_ni.c | 1 +
5 files changed, 154 insertions(+), 64 deletions(-)
diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
index 7a35a6e..98e76bf 100644
--- a/arch/x86/syscalls/syscall_32.tbl
+++ b/arch/x86/syscalls/syscall_32.tbl
@@ -356,3 +356,4 @@
347 i386 process_vm_readv sys_process_vm_readv compat_sys_process_vm_readv
348 i386 process_vm_writev sys_process_vm_writev compat_sys_process_vm_writev
349 i386 kcmp sys_kcmp
+350 i386 init_module_fd sys_init_module_fd
diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
index a582bfe..722476b 100644
--- a/arch/x86/syscalls/syscall_64.tbl
+++ b/arch/x86/syscalls/syscall_64.tbl
@@ -319,6 +319,7 @@
310 64 process_vm_readv sys_process_vm_readv
311 64 process_vm_writev sys_process_vm_writev
312 common kcmp sys_kcmp
+313 common init_module_fd sys_init_module_fd
#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 19439c7..6ee6e31 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -860,4 +860,5 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
unsigned long idx1, unsigned long idx2);
+asmlinkage long sys_init_module_fd(int fd, const char __user *uargs);
#endif
diff --git a/kernel/module.c b/kernel/module.c
index 4edbd9c..c1e446e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -21,6 +21,7 @@
#include <linux/ftrace_event.h>
#include <linux/init.h>
#include <linux/kallsyms.h>
+#include <linux/file.h>
#include <linux/fs.h>
#include <linux/sysfs.h>
#include <linux/kernel.h>
@@ -2399,48 +2400,102 @@ static inline void kmemleak_load_module(const struct module *mod,
}
#endif
+/* Sanity checks against invalid binaries, wrong arch, weird elf version. */
+static int check_info(struct load_info *info)
+{
+ if (info->len < sizeof(*(info->hdr)))
+ return -ENOEXEC;
+
+ if (memcmp(info->hdr->e_ident, ELFMAG, SELFMAG) != 0
+ || info->hdr->e_type != ET_REL
+ || !elf_check_arch(info->hdr)
+ || info->hdr->e_shentsize != sizeof(Elf_Shdr))
+ return -ENOEXEC;
+
+ if (info->hdr->e_shoff >= info->len
+ || (info->hdr->e_shnum * sizeof(Elf_Shdr) >
+ info->len - info->hdr->e_shoff))
+ return -ENOEXEC;
+
+ return 0;
+}
+
/* Sets info->hdr and info->len. */
-static int copy_and_check(struct load_info *info,
- const void __user *umod, unsigned long len,
- const char __user *uargs)
+int copy_module_from_user(const void __user *umod, unsigned long len,
+ struct load_info *info)
{
int err;
- Elf_Ehdr *hdr;
- if (len < sizeof(*hdr))
+ info->len = len;
+ if (info->len < sizeof(*(info->hdr)))
return -ENOEXEC;
/* Suck in entire file: we'll want most of it. */
- if ((hdr = vmalloc(len)) == NULL)
+ info->hdr = vmalloc(info->len);
+ if (!info->hdr)
return -ENOMEM;
- if (copy_from_user(hdr, umod, len) != 0) {
- err = -EFAULT;
+ err = copy_from_user(info->hdr, umod, info->len);
+ if (err)
goto free_hdr;
- }
- /* Sanity checks against insmoding binaries or wrong arch,
- weird elf version */
- if (memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0
- || hdr->e_type != ET_REL
- || !elf_check_arch(hdr)
- || hdr->e_shentsize != sizeof(Elf_Shdr)) {
- err = -ENOEXEC;
+ err = check_info(info);
+ if (err)
goto free_hdr;
+
+ return err;
+
+free_hdr:
+ vfree(info->hdr);
+ return err;
+}
+
+/* Sets info->hdr and info->len. */
+int copy_module_from_fd(int fd, struct load_info *info)
+{
+ struct file *file;
+ int err;
+ struct kstat stat;
+ unsigned long size;
+ off_t pos;
+ ssize_t bytes = 0;
+
+ file = fget(fd);
+ if (!file)
+ return -ENOEXEC;
+
+ err = vfs_getattr(file->f_vfsmnt, file->f_dentry, &stat);
+ if (err)
+ goto out;
+
+ size = stat.size;
+ info->hdr = vmalloc(size);
+ if (!info->hdr) {
+ err = -ENOMEM;
+ goto out;
}
- if (hdr->e_shoff >= len ||
- hdr->e_shnum * sizeof(Elf_Shdr) > len - hdr->e_shoff) {
- err = -ENOEXEC;
- goto free_hdr;
+ pos = 0;
+ while (pos < size) {
+ bytes = kernel_read(file, pos, (char *)(info->hdr) + pos,
+ size - pos);
+ if (bytes < 0) {
+ vfree(info->hdr);
+ err = bytes;
+ goto out;
+ }
+ if (bytes == 0)
+ break;
+ pos += bytes;
}
+ info->len = pos;
- info->hdr = hdr;
- info->len = len;
- return 0;
+ err = check_info(info);
+ if (err)
+ vfree(info->hdr);
-free_hdr:
- vfree(hdr);
+out:
+ fput(file);
return err;
}
@@ -2861,26 +2916,17 @@ static int post_relocation(struct module *mod, const struct load_info *info)
return module_finalize(info->hdr, info->sechdrs, mod);
}
+static int do_init_module(struct module *mod);
+
/* Allocate and load the module: note that size of section 0 is always
zero, and we rely on this for optional sections. */
-static struct module *load_module(void __user *umod,
- unsigned long len,
- const char __user *uargs)
+static int load_module(struct load_info *info, const char __user *uargs)
{
- struct load_info info = { NULL, };
struct module *mod;
long err;
- pr_debug("load_module: umod=%p, len=%lu, uargs=%p\n",
- umod, len, uargs);
-
- /* Copy in the blobs from userspace, check they are vaguely sane. */
- err = copy_and_check(&info, umod, len, uargs);
- if (err)
- return ERR_PTR(err);
-
/* Figure out module layout, and allocate all the memory. */
- mod = layout_and_allocate(&info);
+ mod = layout_and_allocate(info);
if (IS_ERR(mod)) {
err = PTR_ERR(mod);
goto free_copy;
@@ -2893,25 +2939,25 @@ static struct module *load_module(void __user *umod,
/* Now we've got everything in the final locations, we can
* find optional sections. */
- find_module_sections(mod, &info);
+ find_module_sections(mod, info);
err = check_module_license_and_versions(mod);
if (err)
goto free_unload;
/* Set up MODINFO_ATTR fields */
- setup_modinfo(mod, &info);
+ setup_modinfo(mod, info);
/* Fix up syms, so that st_value is a pointer to location. */
- err = simplify_symbols(mod, &info);
+ err = simplify_symbols(mod, info);
if (err < 0)
goto free_modinfo;
- err = apply_relocations(mod, &info);
+ err = apply_relocations(mod, info);
if (err < 0)
goto free_modinfo;
- err = post_relocation(mod, &info);
+ err = post_relocation(mod, info);
if (err < 0)
goto free_modinfo;
@@ -2941,14 +2987,14 @@ static struct module *load_module(void __user *umod,
}
/* This has to be done once we're sure module name is unique. */
- dynamic_debug_setup(info.debug, info.num_debug);
+ dynamic_debug_setup(info->debug, info->num_debug);
/* Find duplicate symbols */
err = verify_export_symbols(mod);
if (err < 0)
goto ddebug;
- module_bug_finalize(info.hdr, info.sechdrs, mod);
+ module_bug_finalize(info->hdr, info->sechdrs, mod);
list_add_rcu(&mod->list, &modules);
mutex_unlock(&module_mutex);
@@ -2959,16 +3005,17 @@ static struct module *load_module(void __user *umod,
goto unlink;
/* Link in to syfs. */
- err = mod_sysfs_setup(mod, &info, mod->kp, mod->num_kp);
+ err = mod_sysfs_setup(mod, info, mod->kp, mod->num_kp);
if (err < 0)
goto unlink;
/* Get rid of temporary copy. */
- free_copy(&info);
+ free_copy(info);
/* Done! */
trace_module_load(mod);
- return mod;
+
+ return do_init_module(mod);
unlink:
mutex_lock(&module_mutex);
@@ -2977,7 +3024,7 @@ static struct module *load_module(void __user *umod,
module_bug_cleanup(mod);
ddebug:
- dynamic_debug_remove(info.debug);
+ dynamic_debug_remove(info->debug);
unlock:
mutex_unlock(&module_mutex);
synchronize_sched();
@@ -2989,10 +3036,10 @@ static struct module *load_module(void __user *umod,
free_unload:
module_unload_free(mod);
free_module:
- module_deallocate(mod, &info);
+ module_deallocate(mod, info);
free_copy:
- free_copy(&info);
- return ERR_PTR(err);
+ free_copy(info);
+ return err;
}
/* Call module constructors. */
@@ -3007,21 +3054,10 @@ static void do_mod_ctors(struct module *mod)
}
/* This is where the real work happens */
-SYSCALL_DEFINE3(init_module, void __user *, umod,
- unsigned long, len, const char __user *, uargs)
+static int do_init_module(struct module *mod)
{
- struct module *mod;
int ret = 0;
- /* Must have permission */
- if (!capable(CAP_SYS_MODULE) || modules_disabled)
- return -EPERM;
-
- /* Do all the hard work */
- mod = load_module(umod, len, uargs);
- if (IS_ERR(mod))
- return PTR_ERR(mod);
-
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_COMING, mod);
@@ -3091,6 +3127,56 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
return 0;
}
+static int init_module_permission(void)
+{
+ /* Must have permission */
+ if (!capable(CAP_SYS_MODULE) || modules_disabled)
+ return -EPERM;
+
+ return 0;
+}
+
+SYSCALL_DEFINE2(init_module_fd, int, fd, const char __user *, uargs)
+{
+ int err;
+ struct load_info info = { };
+
+ err = init_module_permission();
+ if (err)
+ return err;
+
+ pr_debug("init_module_fd: fd=%d, uargs=%p\n", fd, uargs);
+
+ if (fd < 0)
+ return -ENOEXEC;
+
+ err = copy_module_from_fd(fd, &info);
+ if (err)
+ return err;
+
+ return load_module(&info, uargs);
+}
+
+SYSCALL_DEFINE3(init_module, void __user *, umod,
+ unsigned long, len, const char __user *, uargs)
+{
+ int err;
+ struct load_info info = { };
+
+ err = init_module_permission();
+ if (err)
+ return err;
+
+ pr_debug("init_module: umod=%p, len=%lu, uargs=%p\n",
+ umod, len, uargs);
+
+ err = copy_module_from_user(umod, len, &info);
+ if (err)
+ return err;
+
+ return load_module(&info, uargs);
+}
+
static inline int within(unsigned long addr, void *start, unsigned long size)
{
return ((void *)addr >= start && (void *)addr < start + size);
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index dbff751..3195f80 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -25,6 +25,7 @@ cond_syscall(sys_swapoff);
cond_syscall(sys_kexec_load);
cond_syscall(compat_sys_kexec_load);
cond_syscall(sys_init_module);
+cond_syscall(sys_init_module_fd);
cond_syscall(sys_delete_module);
cond_syscall(sys_socketpair);
cond_syscall(sys_bind);
--
1.7.0.4
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