While discussing[1] the need for glibc to have access to random bytes
during program load, it seems that an earlier attempt to implement
AT_RANDOM got stalled. This implements a configurable number of random
bytes available to every ELF program via a new auxv AT_RANDOM vector.
[1] http://sourceware.org/ml/libc-alpha/2008-10/msg00006.html
Signed-off-by: Kees Cook <kees.cook@canonical.com>
---
fs/binfmt_elf.c | 20 ++++++++++++++++++++
include/linux/auxvec.h | 4 +++-
security/Kconfig | 9 +++++++++
3 files changed, 32 insertions(+), 1 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 655ed8d..9b2ea62 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -152,6 +152,8 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
elf_addr_t __user *sp;
elf_addr_t __user *u_platform;
elf_addr_t __user *u_base_platform;
+ elf_addr_t __user *u_rand_bytes;
+ unsigned int rand_size;
const char *k_platform = ELF_PLATFORM;
const char *k_base_platform = ELF_BASE_PLATFORM;
int items;
@@ -196,6 +198,18 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
return -EFAULT;
}
+ rand_size = CONFIG_SECURITY_AUXV_RANDOM_SIZE * sizeof(unsigned long);
+ u_rand_bytes = NULL;
+ if (rand_size) {
+ unsigned char k_rand_bytes[CONFIG_SECURITY_AUXV_RANDOM_SIZE *
+ sizeof(unsigned long)];
+ get_random_bytes(k_rand_bytes, rand_size);
+
+ u_rand_bytes = (elf_addr_t __user *)STACK_ALLOC(p, rand_size);
+ if (__copy_to_user(u_rand_bytes, k_rand_bytes, rand_size))
+ return -EFAULT;
+ }
+
/* Create the ELF interpreter info */
elf_info = (elf_addr_t *)current->mm->saved_auxv;
/* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */
@@ -228,6 +242,12 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
NEW_AUX_ENT(AT_GID, tsk->gid);
NEW_AUX_ENT(AT_EGID, tsk->egid);
NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ if (rand_size) {
+ NEW_AUX_ENT(AT_RANDOM_SIZE,
+ (elf_addr_t)(unsigned long)rand_size);
+ NEW_AUX_ENT(AT_RANDOM,
+ (elf_addr_t)(unsigned long)u_rand_bytes);
+ }
NEW_AUX_ENT(AT_EXECFN, bprm->exec);
if (k_platform) {
NEW_AUX_ENT(AT_PLATFORM,
diff --git a/include/linux/auxvec.h b/include/linux/auxvec.h
index d7afa9d..df4ff65 100644
--- a/include/linux/auxvec.h
+++ b/include/linux/auxvec.h
@@ -23,6 +23,8 @@
#define AT_PLATFORM 15 /* string identifying CPU for optimizations */
#define AT_HWCAP 16 /* arch dependent hints at CPU capabilities */
#define AT_CLKTCK 17 /* frequency at which times() increments */
+#define AT_RANDOM 18 /* address of random bytes */
+#define AT_RANDOM_SIZE 19 /* number of random bytes at AT_RANDOM */
#define AT_SECURE 23 /* secure mode boolean */
@@ -32,7 +34,7 @@
#define AT_EXECFN 31 /* filename of program */
#ifdef __KERNEL__
-#define AT_VECTOR_SIZE_BASE 18 /* NEW_AUX_ENT entries in auxiliary table */
+#define AT_VECTOR_SIZE_BASE 20 /* NEW_AUX_ENT entries in auxiliary table */
/* number of "#define AT_.*" above, minus {AT_NULL, AT_IGNORE, AT_NOTELF} */
#endif
diff --git a/security/Kconfig b/security/Kconfig
index f6c0429..8d9d49d 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -114,6 +114,15 @@ config SECURITY_DEFAULT_MMAP_MIN_ADDR
This value can be changed after boot using the
/proc/sys/vm/mmap_min_addr tunable.
+config SECURITY_AUXV_RANDOM_SIZE
+ int "Number of random longs to store in AT_RANDOM on every exec"
+ default 4
+ help
+ This value determines the size of the random longs provided
+ to programs via the auxv AT_RANDOM vector. It can be used
+ to initialize random values needed during program load.
+
+ If you are unsure how many longs to use, answer 4.
source security/selinux/Kconfig
source security/smack/Kconfig
--
1.5.6.3
--
Kees Cook
Ubuntu Security Team
--
