From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 27 Apr 2022 00:09:44 +0300 From: Vitaly Chikunov To: ALT Linux kernel packages development Message-ID: <20220426210944.zio64lx5gg3ayq52@altlinux.org> References: <20220426094733.1872052-1-vseleznv@altlinux.org> <20220426094733.1872052-2-vseleznv@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=koi8-r Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220426094733.1872052-2-vseleznv@altlinux.org> Subject: Re: [d-kernel] [PATCH] AltHa: nosuid handles capabilities as well X-BeenThere: devel-kernel@lists.altlinux.org X-Mailman-Version: 2.1.12 Precedence: list Reply-To: ALT Linux kernel packages development List-Id: ALT Linux kernel packages development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Apr 2022 21:09:44 -0000 Archived-At: List-Archive: List-Post: Vladimir, On Tue, Apr 26, 2022 at 09:47:33AM +0000, Vladimir D. Seleznev wrote: > Signed-off-by: Vladimir D. Seleznev > --- > Documentation/admin-guide/LSM/AltHa.rst | 6 ++-- > security/altha/altha_lsm.c | 37 ++++++++++++++++++++----- > 2 files changed, 33 insertions(+), 10 deletions(-) > > diff --git a/Documentation/admin-guide/LSM/AltHa.rst b/Documentation/admin-guide/LSM/AltHa.rst > index be698709d3f0..beda40601c9e 100644 > --- a/Documentation/admin-guide/LSM/AltHa.rst > +++ b/Documentation/admin-guide/LSM/AltHa.rst > @@ -3,7 +3,7 @@ AltHa > ==== > > AltHa is a Linux Security Module currently has three userspace hardening options: > - * ignore SUID on binaries (with exceptions possible); > + * ignore SUID and setcaps on binaries (with exceptions possible); > * prevent running selected script interpreters in interactive mode; > * disable open file unlinking in selected dirs. > * enable kiosk mode > @@ -15,12 +15,12 @@ through sysctls in ``/proc/sys/kernel/altha``. > > NoSUID > ============ > -Modern Linux systems can be used with minimal (or even zero at least for OWL and ALT) usage of SUID programms, but in many cases in full-featured desktop or server systems there are plenty of them: uncounted and sometimes unnecessary. Privileged programms are always an attack surface, but mounting filesystems with ``nosuid`` flag doesn't provide enough granularity in SUID binaries management. This LSM module provides a single control point for all SUID binaries. When this submodule is enabled, SUID bits on all binaries except explicitly listed are system-wide ignored. > +Modern Linux systems can be used with minimal (or even zero at least for OWL and ALT) usage of SUID programms, but in many cases in full-featured desktop or server systems there are plenty of them: uncounted and sometimes unnecessary. Privileged programms are always an attack surface, but mounting filesystems with ``nosuid`` flag doesn't provide enough granularity in SUID binaries management. This LSM module provides a single control point for all SUID and setcap binaries. When this submodule is enabled, SUID and setcap bits on all binaries except explicitly listed are system-wide ignored. > > Sysctl parameters and defaults: > > * ``kernel.altha.nosuid.enabled = 0``, set to 1 to enable > -* ``kernel.altha.nosuid.exceptions =``, colon-separated list of enabled SUID binaries, for example: ``/bin/su:/usr/libexec/hasher-priv/hasher-priv`` > +* ``kernel.altha.nosuid.exceptions =``, colon-separated list of enabled SUID and setcap binaries, for example: ``/bin/su:/usr/libexec/hasher-priv/hasher-priv`` > > RestrScript > ============ > diff --git a/security/altha/altha_lsm.c b/security/altha/altha_lsm.c > index c670ad7ed458..5f0505a51644 100644 > --- a/security/altha/altha_lsm.c > +++ b/security/altha/altha_lsm.c > @@ -11,6 +11,7 @@ > > #include > #include > +#include > #include > #include > #include > @@ -237,10 +238,20 @@ int is_olock_dir(struct inode *inode) > return 0; > } > > +static int has_any_caps(struct cred *cred) > +{ > + return !cap_isclear(cred->cap_permitted) || > + !cap_isclear(cred->cap_effective); > + > + return 0; > +} > + > /* Hooks */ > static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * fi) > { > struct altha_list_struct *node; > + int is_set_caps = 0; > + char *set_uid_cap = "setuid"; > /* when it's not a shebang issued script interpreter */ > if (rstrscript_enabled && bprm->executable == bprm->interpreter) { > char *path_p; > @@ -267,11 +278,18 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f > up_read(&interpreters_sem); > kfree(path_buffer); > } > - if (unlikely(nosuid_enabled && > - !uid_eq(bprm->cred->uid, bprm->cred->euid))) { > + if (nosuid_enabled) { > char *path_p; > char *path_buffer; > uid_t cur_uid; > + uid_t cur_euid = from_kuid(bprm->cred->user_ns, bprm->cred->euid); > + /* Check for any caps for non-superuser. */ > + if (cur_euid != (uid_t) 0 > + && has_any_caps(bprm->cred)) { Логика этого не понятна. Было бы неплохо чтоб она была пояснена в комментариях чтоб и простые люди могли её понять. Почему caps проверяются только для non-superuser? Ведь и superuser может сбрасывать capabilities. У superuser может не быть каких-то capabilities вплоть до никаких, кроме его uid 0. Следовательно, установка new capabilities не должна зависеть от uid. Далее, capabilities могут устанавливаться не все, но если в этой проверке были обнаружены capabilities, то далее suid игнорируются и не сбрасываются если они были. Что будет если установлены одновременно и setcap, и suid? Неплохо было бы, чтоб это все было пояснено в комментариях. Например, почему не важно не сбрасывать suid при setcap. Thanks, > + is_set_caps = 1; > + set_uid_cap = "setcap"; > + } else if (uid_eq(bprm->cred->uid, bprm->cred->euid)) > + return 0; > > path_buffer = kmalloc(PATH_MAX, GFP_KERNEL); > if (!path_buffer) > @@ -283,8 +301,8 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f > list_for_each_entry(node, &nosuid_exceptions_list, list) { > if (strcmp(path_p, node->spath) == 0) { > pr_notice_ratelimited > - ("AltHa/NoSUID: %s permitted to setuid from %d\n", > - bprm->filename, cur_uid); > + ("AltHa/NoSUID: %s permitted to %s from %d\n", > + bprm->filename, set_uid_cap, cur_uid); > up_read(&nosuid_exceptions_sem); > kfree(path_buffer); > return 0; > @@ -292,9 +310,14 @@ static int altha_bprm_creds_from_file(struct linux_binprm *bprm, struct file * f > } > up_read(&nosuid_exceptions_sem); > pr_notice_ratelimited > - ("AltHa/NoSUID: %s prevented to setuid from %d\n", > - bprm->filename, cur_uid); > - bprm->cred->euid = bprm->cred->uid; > + ("AltHa/NoSUID: %s prevented to %s from %d\n", > + bprm->filename, set_uid_cap, cur_uid); > + if (is_set_caps) { > + cap_clear(bprm->cred->cap_inheritable); > + cap_clear(bprm->cred->cap_permitted); > + cap_clear(bprm->cred->cap_effective); > + } else > + bprm->cred->euid = bprm->cred->uid; > kfree(path_buffer); > } > return 0; > -- > 2.33.2 > > _______________________________________________ > devel-kernel mailing list > devel-kernel@lists.altlinux.org > https://lists.altlinux.org/mailman/listinfo/devel-kernel