From fede148324c34360ce8c30a9a5bdfac5574b2a59 Mon Sep 17 00:00:00 2001 From: Ondrej Mosnacek Date: Fri, 25 Jan 2019 11:06:51 +0100 Subject: 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 Signed-off-by: Ondrej Mosnacek Reviewed-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/ss/services.c | 37 ++++++++++++++++++++++++++++++++----- 1 file changed, 32 insertions(+), 5 deletions(-) (limited to 'security/selinux/ss/services.c') 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); } /* -- cgit v1.2.3-59-g8ed1b