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authorOndrej Mosnacek <omosnace@redhat.com>2019-01-25 11:06:51 +0100
committerPaul Moore <paul@paul-moore.com>2019-01-25 17:31:14 -0500
commitfede148324c34360ce8c30a9a5bdfac5574b2a59 (patch)
tree6908514ddcc623ad8776f9f58897ee1d07c8f8f1
parent994fb0651d02e49567e7550eb574981b387fc06f (diff)
selinux: log invalid contexts in AVCs
In case a file has an invalid context set, in an AVC record generated upon access to such file, the target context is always reported as unlabeled. This patch adds new optional fields to the AVC record (srawcon and trawcon) that report the actual context string if it differs from the one reported in scontext/tcontext. This is useful for diagnosing SELinux denials involving invalid contexts. To trigger an AVC that illustrates this situation: # setenforce 0 # touch /tmp/testfile # setfattr -n security.selinux -v system_u:object_r:banana_t:s0 /tmp/testfile # runcon system_u:system_r:sshd_t:s0 cat /tmp/testfile AVC before: type=AVC msg=audit(1547801083.248:11): avc: denied { open } for pid=1149 comm="cat" path="/tmp/testfile" dev="tmpfs" ino=6608 scontext=system_u:system_r:sshd_t:s0 tcontext=system_u:object_r:unlabeled_t:s15:c0.c1023 tclass=file permissive=1 AVC after: type=AVC msg=audit(1547801083.248:11): avc: denied { open } for pid=1149 comm="cat" path="/tmp/testfile" dev="tmpfs" ino=6608 scontext=system_u:system_r:sshd_t:s0 tcontext=system_u:object_r:unlabeled_t:s15:c0.c1023 tclass=file permissive=1 trawcon=system_u:object_r:banana_t:s0 Note that it is also possible to encounter this situation with the 'scontext' field - e.g. when a new policy is loaded while a process is running, whose context is not valid in the new policy. Link: https://bugzilla.redhat.com/show_bug.cgi?id=1135683 Cc: Daniel Walsh <dwalsh@redhat.com> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Paul Moore <paul@paul-moore.com>
-rw-r--r--security/selinux/avc.c15
-rw-r--r--security/selinux/include/security.h3
-rw-r--r--security/selinux/ss/services.c37
3 files changed, 50 insertions, 5 deletions
diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 5ebad47391c9..3a27418b20d7 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -734,6 +734,21 @@ static void avc_audit_post_callback(struct audit_buffer *ab, void *a)
if (sad->denied)
audit_log_format(ab, " permissive=%u", sad->result ? 0 : 1);
+
+ /* in case of invalid context report also the actual context string */
+ rc = security_sid_to_context_inval(sad->state, sad->ssid, &scontext,
+ &scontext_len);
+ if (!rc && scontext) {
+ audit_log_format(ab, " srawcon=%s", scontext);
+ kfree(scontext);
+ }
+
+ rc = security_sid_to_context_inval(sad->state, sad->tsid, &scontext,
+ &scontext_len);
+ if (!rc && scontext) {
+ audit_log_format(ab, " trawcon=%s", scontext);
+ kfree(scontext);
+ }
}
/* This is the slow part of avc audit with big stack footprint */
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index ba8eedf42b90..f68fb25b5702 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -255,6 +255,9 @@ int security_sid_to_context(struct selinux_state *state, u32 sid,
int security_sid_to_context_force(struct selinux_state *state,
u32 sid, char **scontext, u32 *scontext_len);
+int security_sid_to_context_inval(struct selinux_state *state,
+ u32 sid, char **scontext, u32 *scontext_len);
+
int security_context_to_sid(struct selinux_state *state,
const char *scontext, u32 scontext_len,
u32 *out_sid, gfp_t gfp);
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index dd44126c8d14..9be05c3e99dc 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1281,7 +1281,8 @@ const char *security_get_initial_sid_context(u32 sid)
static int security_sid_to_context_core(struct selinux_state *state,
u32 sid, char **scontext,
- u32 *scontext_len, int force)
+ u32 *scontext_len, int force,
+ int only_invalid)
{
struct policydb *policydb;
struct sidtab *sidtab;
@@ -1326,8 +1327,14 @@ static int security_sid_to_context_core(struct selinux_state *state,
rc = -EINVAL;
goto out_unlock;
}
- rc = context_struct_to_string(policydb, context, scontext,
- scontext_len);
+ if (only_invalid && !context->len) {
+ scontext = NULL;
+ scontext_len = 0;
+ rc = 0;
+ } else {
+ rc = context_struct_to_string(policydb, context, scontext,
+ scontext_len);
+ }
out_unlock:
read_unlock(&state->ss->policy_rwlock);
out:
@@ -1349,14 +1356,34 @@ int security_sid_to_context(struct selinux_state *state,
u32 sid, char **scontext, u32 *scontext_len)
{
return security_sid_to_context_core(state, sid, scontext,
- scontext_len, 0);
+ scontext_len, 0, 0);
}
int security_sid_to_context_force(struct selinux_state *state, u32 sid,
char **scontext, u32 *scontext_len)
{
return security_sid_to_context_core(state, sid, scontext,
- scontext_len, 1);
+ scontext_len, 1, 0);
+}
+
+/**
+ * security_sid_to_context_inval - Obtain a context for a given SID if it
+ * is invalid.
+ * @sid: security identifier, SID
+ * @scontext: security context
+ * @scontext_len: length in bytes
+ *
+ * Write the string representation of the context associated with @sid
+ * into a dynamically allocated string of the correct size, but only if the
+ * context is invalid in the current policy. Set @scontext to point to
+ * this string (or NULL if the context is valid) and set @scontext_len to
+ * the length of the string (or 0 if the context is valid).
+ */
+int security_sid_to_context_inval(struct selinux_state *state, u32 sid,
+ char **scontext, u32 *scontext_len)
+{
+ return security_sid_to_context_core(state, sid, scontext,
+ scontext_len, 1, 1);
}
/*