Re: [PATCH v2] selinux: log invalid contexts in AVCs

On Mon, Jan 21, 2019 at 10:36 AM Ondrej Mosnacek <omosnace(a)redhat.com&gt; wrote: > 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 trawcon=system_u:object_r:banana_t:s0 tclass=file permissive=1 I would like us to add new fields at the end of existing records; the recent audit config changes are a bit of a special case as discussed previously.

Also, under what cases would we ever see a srawcon field? This is only going to happen if we have a running process whose domain is removed during a policy reload, correct? I'm find with including this for the sake of completeness, but I would mention this in the patch description for the next revision.

> Cc: Daniel Walsh <dwalsh(a)redhat.com&gt; > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1135683 > Signed-off-by: Ondrej Mosnacek <omosnace(a)redhat.com&gt; > --- > > v2: Rename fields to "(s|t)rawcon". > > security/selinux/avc.c | 49 +++++++++++++++++++++++++----------------- > 1 file changed, 29 insertions(+), 20 deletions(-) > > diff --git a/security/selinux/avc.c b/security/selinux/avc.c > index 9b63d8ee1687..df5490db575b 100644 > --- a/security/selinux/avc.c > +++ b/security/selinux/avc.c > @@ -165,6 +165,32 @@ static void avc_dump_av(struct audit_buffer *ab, u16 tclass, u32 av) > audit_log_format(ab, " }"); > } > > +static void avc_dump_sid(struct audit_buffer *ab, struct selinux_state *state, > + u32 sid, char type) > +{ > + int rc; > + char *context, *rcontext; > + u32 context_len, rcontext_len; > + > + rc = security_sid_to_context(state, sid, &context, &context_len); > + if (rc) { > + audit_log_format(ab, "%csid=%d ", type, sid); > + return; > + } > + > + audit_log_format(ab, "%ccontext=%s ", type, context); > + > + /* in case of invalid context report also the actual context string */ > + rc = security_sid_to_context_force(state, sid, &rcontext, > + &rcontext_len); > + if (!rc) { > + if (strcmp(context, rcontext)) > + audit_log_format(ab, "%crawcon=%s ", type, rcontext); > + kfree(rcontext); > + } > + kfree(context); > +} > + > /** > * avc_dump_query - Display a SID pair and a class in human-readable form. > * @ssid: source security identifier > @@ -174,28 +200,11 @@ static void avc_dump_av(struct audit_buffer *ab, u16 tclass, u32 av) > static void avc_dump_query(struct audit_buffer *ab, struct selinux_state *state, > u32 ssid, u32 tsid, u16 tclass) > { > - int rc; > - char *scontext; > - u32 scontext_len; > - > - rc = security_sid_to_context(state, ssid, &scontext, &scontext_len); > - if (rc) > - audit_log_format(ab, "ssid=%d", ssid); > - else { > - audit_log_format(ab, "scontext=%s", scontext); > - kfree(scontext); > - } > - > - rc = security_sid_to_context(state, tsid, &scontext, &scontext_len); > - if (rc) > - audit_log_format(ab, " tsid=%d", tsid); > - else { > - audit_log_format(ab, " tcontext=%s", scontext); > - kfree(scontext); > - } > + avc_dump_sid(ab, state, ssid, 's'); > + avc_dump_sid(ab, state, tsid, 't'); > > BUG_ON(!tclass || tclass >= ARRAY_SIZE(secclass_map)); > - audit_log_format(ab, " tclass=%s", secclass_map[tclass-1].name); > + audit_log_format(ab, "tclass=%s", secclass_map[tclass-1].name); > } > > /** > -- > 2.20.1 -- paul moore www.paul-moore.com