ipaccess: Fix use-after-free in ipaccess_drop()

Recent commit b8ea0ff521a3e01c22a9dd1948b9a853521f575e introduced a
heap-use-after-free while getting rid of memleaks and clearing up the
reference counting lifecycle of the line object.

In that commit, e1inp_line_put2() was added in ipaccess_drop() which may
potentially free the line object (and its children e1inp_ts objects)
under specific conditions/scenarions. However, the function still used
the child object e1i_ts which in those scenarios would access already
freed memory.

Let's keep a local reference during the life of the function to make
sure the object is non-freed during e1inp_line_put2(), so that we can
notify upper layers that the link is down.

Detected by enabling ASan and running BSC_Tests.TC_chopped_ipa_ping
TTCN3 test.

Related: OS#4688
Change-Id: I4f56af28ad8297846bcdc8ba7afe51fff0f9a00f

1 files changed, 2 insertions, 0 deletions

diff --git a/src/input/ipaccess.c b/src/input/ipaccess.c
index d81191c..30bcaf9 100644
--- a/src/input/ipaccess.c
+++ b/src/input/ipaccess.c
@@ -82,6 +82,7 @@ static int ipaccess_drop(struct osmo_fd *bfd, struct e1inp_line *line)
 {
 	int ret = 1;
 	struct e1inp_ts *e1i_ts = ipaccess_line_ts(bfd, line);
+	e1inp_line_get2(line, __func__);
 
 	ipaccess_keepalive_fsm_cleanup(e1i_ts);
 
@@ -108,6 +109,7 @@ static int ipaccess_drop(struct osmo_fd *bfd, struct e1inp_line *line)
 	/* e1inp_sign_link_destroy releases the socket descriptors for us. */
 	line->ops->sign_link_down(line);
 
+	e1inp_line_put2(line, __func__);
 	return ret;
 }