From 6eb864c1d9dd1ef32b88e03c3f49d8be0dab7dcf Mon Sep 17 00:00:00 2001 From: Mikhail Kurinnoi Date: Wed, 27 Jun 2018 16:33:42 +0300 Subject: [PATCH] integrity: prevent deadlock during digsig verification. This patch aimed to prevent deadlock during digsig verification.The point of issue - user space utility modprobe and/or it's dependencies (ld-*.so, libz.so.*, libc-*.so and /lib/modules/ files) that could be used for kernel modules load during digsig verification and could be signed by digsig in the same time. First at all, look at crypto_alloc_tfm() work algorithm: crypto_alloc_tfm() will first attempt to locate an already loaded algorithm. If that fails and the kernel supports dynamically loadable modules, it will then attempt to load a module of the same name or alias. If that fails it will send a query to any loaded crypto manager to construct an algorithm on the fly. We have situation, when public_key_verify_signature() in case of RSA algorithm use alg_name to store internal information in order to construct an algorithm on the fly, but crypto_larval_lookup() will try to use alg_name in order to load kernel module with same name. 1) we can't do anything with crypto module work, since it designed to work exactly in this way; 2) we can't globally filter module requests for modprobe, since it designed to work with any requests. In this patch, I propose add an exception for "crypto-pkcs1pad(rsa,*)" module requests only in case of enabled integrity asymmetric keys support. Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules for sure, we are safe to fail such module request from crypto_larval_lookup(). In this way we prevent modprobe execution during digsig verification and avoid possible deadlock if modprobe and/or it's dependencies also signed with digsig. Requested "crypto-pkcs1pad(rsa,*)" kernel module name formed by: 1) "pkcs1pad(rsa,%s)" in public_key_verify_signature(); 2) "crypto-%s" / "crypto-%s-all" in crypto_larval_lookup(). "crypto-pkcs1pad(rsa," part of request is a constant and unique and could be used as filter. Signed-off-by: Mikhail Kurinnoi Signed-off-by: Mimi Zohar include/linux/integrity.h | 13 +++++++++++++ security/integrity/digsig_asymmetric.c | 23 +++++++++++++++++++++++ security/security.c | 7 ++++++- 3 files changed, 42 insertions(+), 1 deletion(-) --- include/linux/integrity.h | 13 +++++++++++++ security/integrity/digsig_asymmetric.c | 23 +++++++++++++++++++++++ security/security.c | 7 ++++++- 3 files changed, 42 insertions(+), 1 deletion(-) diff --git a/include/linux/integrity.h b/include/linux/integrity.h index 858d3f4a2241..54c853ec2fd1 100644 --- a/include/linux/integrity.h +++ b/include/linux/integrity.h @@ -44,4 +44,17 @@ static inline void integrity_load_keys(void) } #endif /* CONFIG_INTEGRITY */ +#ifdef CONFIG_INTEGRITY_ASYMMETRIC_KEYS + +extern int integrity_kernel_module_request(char *kmod_name); + +#else + +static inline int integrity_kernel_module_request(char *kmod_name) +{ + return 0; +} + +#endif /* CONFIG_INTEGRITY_ASYMMETRIC_KEYS */ + #endif /* _LINUX_INTEGRITY_H */ diff --git a/security/integrity/digsig_asymmetric.c b/security/integrity/digsig_asymmetric.c index ab6a029062a1..6dc075144508 100644 --- a/security/integrity/digsig_asymmetric.c +++ b/security/integrity/digsig_asymmetric.c @@ -115,3 +115,26 @@ int asymmetric_verify(struct key *keyring, const char *sig, pr_debug("%s() = %d\n", __func__, ret); return ret; } + +/** + * integrity_kernel_module_request - prevent crypto-pkcs1pad(rsa,*) requests + * @kmod_name: kernel module name + * + * We have situation, when public_key_verify_signature() in case of RSA + * algorithm use alg_name to store internal information in order to + * construct an algorithm on the fly, but crypto_larval_lookup() will try + * to use alg_name in order to load kernel module with same name. + * Since we don't have any real "crypto-pkcs1pad(rsa,*)" kernel modules, + * we are safe to fail such module request from crypto_larval_lookup(). + * + * In this way we prevent modprobe execution during digsig verification + * and avoid possible deadlock if modprobe and/or it's dependencies + * also signed with digsig. + */ +int integrity_kernel_module_request(char *kmod_name) +{ + if (strncmp(kmod_name, "crypto-pkcs1pad(rsa,", 20) == 0) + return -EINVAL; + + return 0; +} diff --git a/security/security.c b/security/security.c index b49ee810371b..dbca03d3629b 100644 --- a/security/security.c +++ b/security/security.c @@ -1032,7 +1032,12 @@ int security_kernel_create_files_as(struct cred *new, struct inode *inode) int security_kernel_module_request(char *kmod_name) { - return call_int_hook(kernel_module_request, 0, kmod_name); + int ret; + + ret = call_int_hook(kernel_module_request, 0, kmod_name); + if (ret) + return ret; + return integrity_kernel_module_request(kmod_name); } int security_kernel_read_file(struct file *file, enum kernel_read_file_id id) -- 2.30.2