control_if: Avoid heap-use-after-free in osmo_wqueue_bfd_cb
Imagine following scenario:
1- client connects to CTRL iface, a new conn is created with POLL_READ
enabled.
2- A non-related event happens which triggers a TRAP to be sent. As a
result, the wqueue for the conn has now enabled POLL_WRITE, and message
will be sent next time we go through osmo_main_select().
3- At the same time, we receive the GET cmd from the CTRL client, which
means POLL_READ event will be also triggered next time we call
osmo_main_select().
4- osmo_main_select triggers osmo_wqueue_bfd_cb with both READ/WRITE
flags set.
5- The read_cb of wqueue is executed first. The handler closes the CTRL
conn for some reason, freeing the osmo_fd struct and returns.
6- osmo_qeueue_bfd_cb keeps using the already freed osmo_fd and calls
write_cb.
So in step 6 we get a heap-use-after-free catched by AddressSanitizer:
[0;m20180424135406115 [1;32mDLCTRL[0;m <0018> control_if.c:506 accept()ed new CTRL connection from (r=10.42.42.1:53910<->l=10.42.42.7:4249)
[0;m20180424135406116 [1;34mDLCTRL[0;m <0018> control_cmd.c:378 Command: GET bts.0.oml-connection-state
[0;m20180424135406117 [1;34mDLINP[0;m <0013> bts_ipaccess_nanobts.c:417 Identified BTS 1/0/0
[0;m[1;36m20180424135406118 [1;34mDNM[0;m[1;36m <0005> abis_nm.c:1628 Get Attr (bts=0)
[0;m[1;36m20180424135406118 [1;34mDNM[0;m[1;36m <0005> abis_nm.c:1628 Get Attr (bts=0)
[0;m20180424135406118 [1;34mDCTRL[0;m <000e> osmo_bsc_ctrl.c:158 BTS connection (re)established, sending TRAP.
[0;m20180424135406119 [1;32mDLCTRL[0;m <0018> control_if.c:173 close()d CTRL connection (r=10.42.42.1:53910<->l=10.42.42.7:4249)
[0;m=================================================================
==12301==ERROR: AddressSanitizer: heap-use-after-free on address 0x611000003e04 at pc 0x7f23091c3a2f bp 0x7ffc0cb73ff0 sp 0x7ffc0cb73fe8
READ of size 4 at 0x611000003e04 thread T0
#0 0x7f23091c3a2e in osmo_wqueue_bfd_cb /home/osmocom-build/jenkins/workspace/osmo-gsm-tester_build-osmo-bsc/libosmocore/src/write_queue.c:65
#1 0x7f23091ad5d8 in osmo_fd_disp_fds /home/osmocom-build/jenkins/workspace/osmo-gsm-tester_build-osmo-bsc/libosmocore/src/select.c:216
#2 0x7f23091ad5d8 in osmo_select_main /home/osmocom-build/jenkins/workspace/osmo-gsm-tester_build-osmo-bsc/libosmocore/src/select.c:256
#3 0x56538bdb7a26 in main /home/osmocom-build/jenkins/workspace/osmo-gsm-tester_build-osmo-bsc/osmo-bsc/src/osmo-bsc/osmo_bsc_main.c:532
#4 0x7f23077532e0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202e0)
#5 0x56538bdb8999 in _start (/home/jenkins/workspace/osmo-gsm-tester_run-prod/trial-896/inst/osmo-bsc/bin/osmo-bsc+0x259999)
Fixes: OS#3206
Change-Id: I84d10caaadcfa6bd46ba8756ca89aa0badcfd2e3
diff --git a/include/osmocom/core/write_queue.h b/include/osmocom/core/write_queue.h
index 2303f87..071621d 100644
--- a/include/osmocom/core/write_queue.h
+++ b/include/osmocom/core/write_queue.h
@@ -42,11 +42,11 @@
/*! actual linked list implementing the queue */
struct llist_head msg_queue;
- /*! call-back in case qeueue is readable */
+ /*! call-back in case qeueue is readable. Return -EBADF if fd is freed inside cb. */
int (*read_cb)(struct osmo_fd *fd);
- /*! call-back in case qeueue is writable */
+ /*! call-back in case qeueue is writable. Return -EBADF if fd is freed inside cb. */
int (*write_cb)(struct osmo_fd *fd, struct msgb *msg);
- /*! call-back in case qeueue has exceptions */
+ /*! call-back in case qeueue has exceptions. Return -EBADF if fd is freed inside cb. */
int (*except_cb)(struct osmo_fd *fd);
};