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Registered in England and Wales under Company Registration No. 3798903 Subject: [PATCH 04/24] Enforce module signatures if the kernel is locked down From: David Howells To: torvalds@linux-foundation.org Cc: linux-man@vger.kernel.org, linux-api@vger.kernel.org, jmorris@namei.org, linux-kernel@vger.kernel.org, dhowells@redhat.com, linux-security-module@vger.kernel.org Date: Wed, 11 Apr 2018 17:25:05 +0100 Message-ID: <152346390539.4030.2913584917609215556.stgit@warthog.procyon.org.uk> In-Reply-To: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> References: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: If the kernel is locked down, require that all modules have valid signatures that we can verify or that IMA can validate the file. I have adjusted the errors generated: (1) If there's no signature (ENODATA) or we can't check it (ENOPKG, ENOKEY), then: (a) If signatures are enforced then EKEYREJECTED is returned. (b) If IMA will have validated the image, return 0 (okay). (c) If there's no signature or we can't check it, but the kernel is locked down then EPERM is returned (this is then consistent with other lockdown cases). (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we return the error we got. Note that the X.509 code doesn't check for key expiry as the RTC might not be valid or might not have been transferred to the kernel's clock yet. Signed-off-by: David Howells Reviewed-by: Jiri Bohac cc: "Lee, Chun-Yi" cc: James Morris --- kernel/module.c | 56 ++++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 43 insertions(+), 13 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index a6e43a5806a1..9c1709a05037 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -64,6 +64,7 @@ #include #include #include +#include #include #include "module-internal.h" @@ -2761,10 +2762,12 @@ static inline void kmemleak_load_module(const struct module *mod, #endif #ifdef CONFIG_MODULE_SIG -static int module_sig_check(struct load_info *info, int flags) +static int module_sig_check(struct load_info *info, int flags, + bool can_do_ima_check) { - int err = -ENOKEY; + int err = -ENODATA; const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1; + const char *reason; const void *mod = info->hdr; /* @@ -2779,19 +2782,46 @@ static int module_sig_check(struct load_info *info, int flags) err = mod_verify_sig(mod, &info->len); } - if (!err) { + switch (err) { + case 0: info->sig_ok = true; return 0; - } - /* Not having a signature is only an error if we're strict. */ - if (err == -ENOKEY && !sig_enforce) - err = 0; + /* We don't permit modules to be loaded into trusted kernels + * without a valid signature on them, but if we're not + * enforcing, certain errors are non-fatal. + */ + case -ENODATA: + reason = "Loading of unsigned module"; + goto decide; + case -ENOPKG: + reason = "Loading of module with unsupported crypto"; + goto decide; + case -ENOKEY: + reason = "Loading of module with unavailable key"; + decide: + if (sig_enforce) { + pr_notice("%s is rejected\n", reason); + return -EKEYREJECTED; + } - return err; + if (can_do_ima_check && is_ima_appraise_enabled()) + return 0; + if (kernel_is_locked_down(reason)) + return -EPERM; + return 0; + + /* All other errors are fatal, including nomem, unparseable + * signatures and signature check failures - even if signatures + * aren't required. + */ + default: + return err; + } } #else /* !CONFIG_MODULE_SIG */ -static int module_sig_check(struct load_info *info, int flags) +static int module_sig_check(struct load_info *info, int flags, + bool can_do_ima_check) { return 0; } @@ -3651,13 +3681,13 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname, /* Allocate and load the module: note that size of section 0 is always zero, and we rely on this for optional sections. */ static int load_module(struct load_info *info, const char __user *uargs, - int flags) + int flags, bool can_do_ima_check) { struct module *mod; long err; char *after_dashes; - err = module_sig_check(info, flags); + err = module_sig_check(info, flags, can_do_ima_check); if (err) goto free_copy; @@ -3846,7 +3876,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod, if (err) return err; - return load_module(&info, uargs, 0); + return load_module(&info, uargs, 0, false); } SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) @@ -3873,7 +3903,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) info.hdr = hdr; info.len = size; - return load_module(&info, uargs, flags); + return load_module(&info, uargs, flags, true); } static inline int within(unsigned long addr, void *start, unsigned long size) From mboxrd@z Thu Jan 1 00:00:00 1970 From: dhowells@redhat.com (David Howells) Date: Wed, 11 Apr 2018 17:25:05 +0100 Subject: [PATCH 04/24] Enforce module signatures if the kernel is locked down In-Reply-To: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> References: <152346387861.4030.4408662483445703127.stgit@warthog.procyon.org.uk> Message-ID: <152346390539.4030.2913584917609215556.stgit@warthog.procyon.org.uk> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org If the kernel is locked down, require that all modules have valid signatures that we can verify or that IMA can validate the file. I have adjusted the errors generated: (1) If there's no signature (ENODATA) or we can't check it (ENOPKG, ENOKEY), then: (a) If signatures are enforced then EKEYREJECTED is returned. (b) If IMA will have validated the image, return 0 (okay). (c) If there's no signature or we can't check it, but the kernel is locked down then EPERM is returned (this is then consistent with other lockdown cases). (2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we return the error we got. Note that the X.509 code doesn't check for key expiry as the RTC might not be valid or might not have been transferred to the kernel's clock yet. Signed-off-by: David Howells Reviewed-by: Jiri Bohac cc: "Lee, Chun-Yi" cc: James Morris --- kernel/module.c | 56 ++++++++++++++++++++++++++++++++++++++++++------------- 1 file changed, 43 insertions(+), 13 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index a6e43a5806a1..9c1709a05037 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -64,6 +64,7 @@ #include #include #include +#include #include #include "module-internal.h" @@ -2761,10 +2762,12 @@ static inline void kmemleak_load_module(const struct module *mod, #endif #ifdef CONFIG_MODULE_SIG -static int module_sig_check(struct load_info *info, int flags) +static int module_sig_check(struct load_info *info, int flags, + bool can_do_ima_check) { - int err = -ENOKEY; + int err = -ENODATA; const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1; + const char *reason; const void *mod = info->hdr; /* @@ -2779,19 +2782,46 @@ static int module_sig_check(struct load_info *info, int flags) err = mod_verify_sig(mod, &info->len); } - if (!err) { + switch (err) { + case 0: info->sig_ok = true; return 0; - } - /* Not having a signature is only an error if we're strict. */ - if (err == -ENOKEY && !sig_enforce) - err = 0; + /* We don't permit modules to be loaded into trusted kernels + * without a valid signature on them, but if we're not + * enforcing, certain errors are non-fatal. + */ + case -ENODATA: + reason = "Loading of unsigned module"; + goto decide; + case -ENOPKG: + reason = "Loading of module with unsupported crypto"; + goto decide; + case -ENOKEY: + reason = "Loading of module with unavailable key"; + decide: + if (sig_enforce) { + pr_notice("%s is rejected\n", reason); + return -EKEYREJECTED; + } - return err; + if (can_do_ima_check && is_ima_appraise_enabled()) + return 0; + if (kernel_is_locked_down(reason)) + return -EPERM; + return 0; + + /* All other errors are fatal, including nomem, unparseable + * signatures and signature check failures - even if signatures + * aren't required. + */ + default: + return err; + } } #else /* !CONFIG_MODULE_SIG */ -static int module_sig_check(struct load_info *info, int flags) +static int module_sig_check(struct load_info *info, int flags, + bool can_do_ima_check) { return 0; } @@ -3651,13 +3681,13 @@ static int unknown_module_param_cb(char *param, char *val, const char *modname, /* Allocate and load the module: note that size of section 0 is always zero, and we rely on this for optional sections. */ static int load_module(struct load_info *info, const char __user *uargs, - int flags) + int flags, bool can_do_ima_check) { struct module *mod; long err; char *after_dashes; - err = module_sig_check(info, flags); + err = module_sig_check(info, flags, can_do_ima_check); if (err) goto free_copy; @@ -3846,7 +3876,7 @@ SYSCALL_DEFINE3(init_module, void __user *, umod, if (err) return err; - return load_module(&info, uargs, 0); + return load_module(&info, uargs, 0, false); } SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) @@ -3873,7 +3903,7 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags) info.hdr = hdr; info.len = size; - return load_module(&info, uargs, flags); + return load_module(&info, uargs, flags, true); } static inline int within(unsigned long addr, void *start, unsigned long size) -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html