[LEDE-DEV] [PATCH] uci: fix a potential use-after-free in uci_set()

[Jordan Miner]

When calling uci_set() to update an option, if ptr->o != NULL and
ptr->option == NULL, then uci_expand_ptr() will set ptr->option to
ptr->o->e.name (or the caller could set ptr->option to that value). In
this case, the option will be freed just before calling
uci_alloc_option() with ptr->option, which was just freed.

Signed-off-by: Jordan Miner <jminer7 at gmail.com>
---
 list.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/list.c b/list.c
index 0347138..3c46a0b 100644
--- a/list.c
+++ b/list.c
@@ -666,6 +666,7 @@ int uci_set(struct uci_context *ctx, struct uci_ptr *ptr)
 {
 	/* NB: UCI_INTERNAL use means without delta tracking */
 	bool internal = ctx && ctx->internal;
+	struct uci_option *o;
 
 	UCI_HANDLE_ERR(ctx);
 	uci_expand_ptr(ctx, ptr, false);
@@ -698,8 +699,9 @@ int uci_set(struct uci_context *ctx, struct uci_ptr *ptr)
 		if ((ptr->o->type == UCI_TYPE_STRING) &&
 			!strcmp(ptr->o->v.string, ptr->value))
 			return 0;
-		uci_free_option(ptr->o);
+		o = ptr->o;
 		ptr->o = uci_alloc_option(ptr->s, ptr->option, ptr->value);
+		uci_free_option(o);
 		ptr->last = &ptr->o->e;
 	} else if (ptr->s && ptr->section) { /* update section */
 		char *s = uci_strdup(ctx, ptr->value);
-- 
2.7.4