tbf: Fix dangling m_new_tbf pointer
Currently if a 'new' TBF is freed before the 'old' one (where
old_tbf->m_new_tbf == new_tbf), the old_tbf->m_new_tbf is not cleared
and can be accessed later on. This can lead to inconsistencies or
segmentation faults.
This commit adds m_old_tbf which points back from new_tbf to old_pdf.
m_new_tbf and m_old_tbf are either both set to NULL or one is the
reverse pointer of the other (tbf->m_new_tbf->m_old_tbf == tbf and
tbf->m_old_tbf->m_new_tbf == tbf). It extends set_new_tbf and
tbf_free to update the pointee accordingly.
The TBF test is extended to check this invariant at several places.
Sponsored-by: On-Waves ehf
diff --git a/src/tbf.h b/src/tbf.h
index 69f1f05..1bea31d 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -169,6 +169,7 @@
enum gprs_rlcmac_tbf_ul_ack_state ul_ack_state;
gprs_rlcmac_tbf *m_new_tbf;
+ gprs_rlcmac_tbf *m_old_tbf; /* reverse pointer for m_new_tbf */
enum gprs_rlcmac_tbf_poll_state poll_state;
uint32_t poll_fn; /* frame number to poll */