[OpenWrt-Devel] [PATCH v3] instance: fix pidfile attribute double free crash

[Petr Štetiar]

Hi Petr,
Hi Felix,

seems like more things were wrong with instance_config_move(), some
of the jail attributes were missing as well...

---
Commit a5af33ce9a16 ("instance: strdup string attributes") has
introduced duplication of various string attributes in order to fix
use-after-free, but missed handling of `pidfile` and `seccomp` attribute
cases in instance_config_move() where the new value of `pidfile` or
`seccomp` is being copied/assigned. Source of this values is then
free()d in subsequent call to instance_free() and then again for 2nd
time during the service stop command handling, leading to double free
crash:

 #0  unmap_chunk at src/malloc/malloc.c:515
 #1  free at src/malloc/malloc.c:526
 #2  instance_free (in=0xd5e300) at instance.c:1100
 #3  instance_delete (in=0xd5e300) at instance.c:559
 #4  instance_stop (in=0xd5e300, halt=true) at instance.c:611

Ref: FS#2723
Fixes: a5af33ce9a16 ("instance: strdup string attributes")
Signed-off-by: Petr Štetiar <ynezz at true.cz>
Signed-off-by: Daniel Golle <daniel at makrotopia.org>
---
 service/instance.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/service/instance.c b/service/instance.c
index ce5b0bf..c2ebc76 100644
--- a/service/instance.c
+++ b/service/instance.c
@@ -1040,17 +1040,39 @@ instance_config_move(struct service_instance *in, struct service_instance *in_sr
 	blobmsg_list_move(&in->jail.mount, &in_src->jail.mount);
 	in->trigger = in_src->trigger;
 	in->command = in_src->command;
-	in->pidfile = in_src->pidfile;
 	in->respawn = in_src->respawn;
 	in->respawn_retry = in_src->respawn_retry;
 	in->respawn_threshold = in_src->respawn_threshold;
 	in->respawn_timeout = in_src->respawn_timeout;
 	in->name = in_src->name;
 	in->trace = in_src->trace;
-	in->seccomp = in_src->seccomp;
 	in->node.avl.key = in_src->node.avl.key;
 	in->syslog_facility = in_src->syslog_facility;
 
+	free(in->pidfile);
+	if (in_src->pidfile)
+		in->pidfile = strdup(in_src->pidfile);
+	else
+		in->pidfile = NULL;
+
+	free(in->seccomp);
+	if (in_src->seccomp)
+		in->seccomp = strdup(in_src->seccomp);
+	else
+		in->seccomp = NULL;
+
+	free(in->jail.name);
+	if (in_src->jail.name)
+		in->jail.name = strdup(in_src->jail.name);
+	else
+		in->jail.name = NULL;
+
+	free(in->jail.hostname);
+	if (in_src->jail.hostname)
+		in->jail.hostname = strdup(in_src->jail.hostname);
+	else
+		in->jail.hostname = NULL;
+
 	free(in->config);
 	in->config = in_src->config;
 	in_src->config = NULL;
-- 
2.24.1


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