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19 Nov 2019 18:46:37 +0000 Received: from moss-pluto.infosec.tycho.ncsc.mil (moss-pluto [192.168.25.131]) by tarius.tycho.ncsc.mil (8.14.4/8.14.4) with ESMTP id xAJIkbj2004921; Tue, 19 Nov 2019 13:46:37 -0500 Subject: Re: [RFC PATCH 2/2] selinux: Propagate RCU walk status from 'security_inode_follow_link()' To: Will Deacon , selinux@vger.kernel.org Cc: linux-kernel@vger.kernel.org References: <20191119184057.14961-1-will@kernel.org> <20191119184057.14961-3-will@kernel.org> From: Stephen Smalley Message-ID: Date: Tue, 19 Nov 2019 13:46:37 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20191119184057.14961-3-will@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: selinux-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On 11/19/19 1:40 PM, Will Deacon wrote: > 'selinux_inode_follow_link()' can be called as part of an RCU path walk, > and is passed a 'bool rcu' parameter to indicate whether or not it is > being called from within an RCU read-side critical section. > > Unfortunately, this knowledge is not propagated further and, instead, > 'avc_has_perm()' unconditionally passes a flags argument of '0' to both > 'avc_has_perm_noaudit()' and 'avc_audit()' which may block. > > Introduce 'avc_has_perm_flags()' which can be used safely from within an > RCU read-side critical section. Please see e46e01eebbbcf2ff6d28ee7cae9f117e9d1572c8 ("selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link"). > > Signed-off-by: Will Deacon > --- > security/selinux/avc.c | 12 +++++++----- > security/selinux/hooks.c | 5 +++-- > security/selinux/include/avc.h | 12 ++++++++---- > 3 files changed, 18 insertions(+), 11 deletions(-) > > diff --git a/security/selinux/avc.c b/security/selinux/avc.c > index 9c183c899e92..7d99dadd24d0 100644 > --- a/security/selinux/avc.c > +++ b/security/selinux/avc.c > @@ -1177,11 +1177,12 @@ inline int avc_has_perm_noaudit(struct selinux_state *state, > } > > /** > - * avc_has_perm - Check permissions and perform any appropriate auditing. > + * avc_has_perm_flags - Check permissions and perform any appropriate auditing. > * @ssid: source security identifier > * @tsid: target security identifier > * @tclass: target security class > * @requested: requested permissions, interpreted based on @tclass > + * @flags: AVC_STRICT, AVC_NONBLOCKING, or 0 > * @auditdata: auxiliary audit data > * > * Check the AVC to determine whether the @requested permissions are granted > @@ -1192,17 +1193,18 @@ inline int avc_has_perm_noaudit(struct selinux_state *state, > * permissions are granted, -%EACCES if any permissions are denied, or > * another -errno upon other errors. > */ > -int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, > - u32 requested, struct common_audit_data *auditdata) > +int avc_has_perm_flags(struct selinux_state *state, u32 ssid, u32 tsid, > + u16 tclass, u32 requested, unsigned int flags, > + struct common_audit_data *auditdata) > { > struct av_decision avd; > int rc, rc2; > > - rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, 0, > + rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, flags, > &avd); > > rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc, > - auditdata, 0); > + auditdata, flags); > if (rc2) > return rc2; > return rc; > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index 9625b99e677f..0c09f59a2740 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -3008,8 +3008,9 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode, > if (IS_ERR(isec)) > return PTR_ERR(isec); > > - return avc_has_perm(&selinux_state, > - sid, isec->sid, isec->sclass, FILE__READ, &ad); > + return avc_has_perm_flags(&selinux_state, sid, isec->sid, isec->sclass, > + rcu ? AVC_NONBLOCKING : 0, > + FILE__READ, &ad); > } > > static noinline int audit_inode_permission(struct inode *inode, > diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h > index 7be0e1e90e8b..0450e1b88182 100644 > --- a/security/selinux/include/avc.h > +++ b/security/selinux/include/avc.h > @@ -149,10 +149,14 @@ int avc_has_perm_noaudit(struct selinux_state *state, > unsigned flags, > struct av_decision *avd); > > -int avc_has_perm(struct selinux_state *state, > - u32 ssid, u32 tsid, > - u16 tclass, u32 requested, > - struct common_audit_data *auditdata); > +int avc_has_perm_flags(struct selinux_state *state, > + u32 ssid, u32 tsid, > + u16 tclass, u32 requested, > + unsigned flags, > + struct common_audit_data *auditdata); > + > +#define avc_has_perm(state, ssid, tsid, tclass, requested, auditdata) \ > + avc_has_perm_flags(state, ssid, tsid, tclass, requested, 0, auditdata) > > int avc_has_extended_perms(struct selinux_state *state, > u32 ssid, u32 tsid, u16 tclass, u32 requested, >