From: Ondrej Mosnacek omosnace@redhat.com
commit 2a5243937c700ffe6a28e6557a4562a9ab0a17a4 upstream.
string_to_context_struct() may garble the context string, so we need to copy back the contents again from the old context struct to avoid storing the corrupted context.
Since string_to_context_struct() tokenizes (and therefore truncates) the context string and we are later potentially copying it with kstrdup(), this may eventually cause pieces of uninitialized kernel memory to be disclosed to userspace (when copying to userspace based on the stored length and not the null character).
How to reproduce on Fedora and similar: # dnf install -y memcached # systemctl start memcached # semodule -d memcached # load_policy # load_policy # systemctl stop memcached # ausearch -m AVC type=AVC msg=audit(1570090572.648:313): avc: denied { signal } for pid=1 comm="systemd" scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:unlabeled_t:s0 tclass=process permissive=0 trawcon=73797374656D5F75007400000000000070BE6E847296FFFF726F6D000096FFFF76
Cc: stable@vger.kernel.org Reported-by: Milos Malik mmalik@redhat.com Fixes: ee1a84fdfeed ("selinux: overhaul sidtab to fix bug and improve performance") Signed-off-by: Ondrej Mosnacek omosnace@redhat.com Acked-by: Stephen Smalley sds@tycho.nsa.gov Signed-off-by: Paul Moore paul@paul-moore.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/selinux/ss/services.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
--- a/security/selinux/ss/services.c +++ b/security/selinux/ss/services.c @@ -1946,7 +1946,14 @@ static int convert_context(struct contex rc = string_to_context_struct(args->newp, NULL, s, newc, SECSID_NULL); if (rc == -EINVAL) { - /* Retain string representation for later mapping. */ + /* + * Retain string representation for later mapping. + * + * IMPORTANT: We need to copy the contents of oldc->str + * back into s again because string_to_context_struct() + * may have garbled it. + */ + memcpy(s, oldc->str, oldc->len); context_init(newc); newc->str = s; newc->len = oldc->len;