From: Stephen Smalley sds@tycho.nsa.gov
[ Upstream commit 0188d5c025ca8fe756ba3193bd7d150139af5a88 ]
commit bda0be7ad994 ("security: make inode_follow_link RCU-walk aware") passed down the rcu flag to the SELinux AVC, but failed to adjust the test in slow_avc_audit() to also return -ECHILD on LSM_AUDIT_DATA_DENTRY. Previously, we only returned -ECHILD if generating an audit record with LSM_AUDIT_DATA_INODE since this was only relevant from inode_permission. Move the handling of MAY_NOT_BLOCK to avc_audit() and its inlined equivalent in selinux_inode_permission() immediately after we determine that audit is required, and always fall back to ref-walk in this case.
Fixes: bda0be7ad994 ("security: make inode_follow_link RCU-walk aware") Reported-by: Will Deacon will@kernel.org Suggested-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Stephen Smalley sds@tycho.nsa.gov Signed-off-by: Paul Moore paul@paul-moore.com Signed-off-by: Sasha Levin sashal@kernel.org --- security/selinux/avc.c | 24 +++++------------------- security/selinux/hooks.c | 11 +++++++---- security/selinux/include/avc.h | 8 +++++--- 3 files changed, 17 insertions(+), 26 deletions(-)
diff --git a/security/selinux/avc.c b/security/selinux/avc.c index 5de18a6d5c3f0..0622cae510461 100644 --- a/security/selinux/avc.c +++ b/security/selinux/avc.c @@ -496,7 +496,7 @@ static inline int avc_xperms_audit(struct selinux_state *state, if (likely(!audited)) return 0; return slow_avc_audit(state, ssid, tsid, tclass, requested, - audited, denied, result, ad, 0); + audited, denied, result, ad); }
static void avc_node_free(struct rcu_head *rhead) @@ -766,8 +766,7 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a) noinline int slow_avc_audit(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, u32 requested, u32 audited, u32 denied, int result, - struct common_audit_data *a, - unsigned int flags) + struct common_audit_data *a) { struct common_audit_data stack_data; struct selinux_audit_data sad; @@ -777,17 +776,6 @@ noinline int slow_avc_audit(struct selinux_state *state, a->type = LSM_AUDIT_DATA_NONE; }
- /* - * When in a RCU walk do the audit on the RCU retry. This is because - * the collection of the dname in an inode audit message is not RCU - * safe. Note this may drop some audits when the situation changes - * during retry. However this is logically just as if the operation - * happened a little later. - */ - if ((a->type == LSM_AUDIT_DATA_INODE) && - (flags & MAY_NOT_BLOCK)) - return -ECHILD; - sad.tclass = tclass; sad.requested = requested; sad.ssid = ssid; @@ -860,16 +848,14 @@ static int avc_update_node(struct selinux_avc *avc, /* * If we are in a non-blocking code path, e.g. VFS RCU walk, * then we must not add permissions to a cache entry - * because we cannot safely audit the denial. Otherwise, + * because we will not audit the denial. Otherwise, * during the subsequent blocking retry (e.g. VFS ref walk), we * will find the permissions already granted in the cache entry * and won't audit anything at all, leading to silent denials in * permissive mode that only appear when in enforcing mode. * - * See the corresponding handling in slow_avc_audit(), and the - * logic in selinux_inode_follow_link and selinux_inode_permission - * for the VFS MAY_NOT_BLOCK flag, which is transliterated into - * AVC_NONBLOCKING for avc_has_perm_noaudit(). + * See the corresponding handling of MAY_NOT_BLOCK in avc_audit() + * and selinux_inode_permission(). */ if (flags & AVC_NONBLOCKING) return 0; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 040c843968dc6..c574285966f9d 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3171,8 +3171,7 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode,
static noinline int audit_inode_permission(struct inode *inode, u32 perms, u32 audited, u32 denied, - int result, - unsigned flags) + int result) { struct common_audit_data ad; struct inode_security_struct *isec = inode->i_security; @@ -3183,7 +3182,7 @@ static noinline int audit_inode_permission(struct inode *inode,
rc = slow_avc_audit(&selinux_state, current_sid(), isec->sid, isec->sclass, perms, - audited, denied, result, &ad, flags); + audited, denied, result, &ad); if (rc) return rc; return 0; @@ -3230,7 +3229,11 @@ static int selinux_inode_permission(struct inode *inode, int mask) if (likely(!audited)) return rc;
- rc2 = audit_inode_permission(inode, perms, audited, denied, rc, flags); + /* fall back to ref-walk if we have to generate audit */ + if (flags & MAY_NOT_BLOCK) + return -ECHILD; + + rc2 = audit_inode_permission(inode, perms, audited, denied, rc); if (rc2) return rc2; return rc; diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h index 74ea50977c201..cf4cc3ef959b5 100644 --- a/security/selinux/include/avc.h +++ b/security/selinux/include/avc.h @@ -100,8 +100,7 @@ static inline u32 avc_audit_required(u32 requested, int slow_avc_audit(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, u32 requested, u32 audited, u32 denied, int result, - struct common_audit_data *a, - unsigned flags); + struct common_audit_data *a);
/** * avc_audit - Audit the granting or denial of permissions. @@ -135,9 +134,12 @@ static inline int avc_audit(struct selinux_state *state, audited = avc_audit_required(requested, avd, result, 0, &denied); if (likely(!audited)) return 0; + /* fall back to ref-walk if we have to generate audit */ + if (flags & MAY_NOT_BLOCK) + return -ECHILD; return slow_avc_audit(state, ssid, tsid, tclass, requested, audited, denied, result, - a, flags); + a); }
#define AVC_STRICT 1 /* Ignore permissive mode. */