tools/thermal: fix memory leak in realloc failure handling

In the previous code, there was a memory leak issue where the previously allocated memory was not freed upon a failed realloc operation. This patch addresses the problem by releasing the old memory before setting the pointer to NULL in case of a realloc failure. This ensures that memory is properly managed and avoids potential memory leaks.

---
 tools/thermal/lib/mainloop.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index 94cbbcbd1c14..6dcc4090d47e 100644
@@ -62,9 +62,13 @@ int mainloop_add(int fd, mainloop_callback_t cb, void *data)
 	struct mainloop_data *md;
 
 	if (fd >= nrhandler) {
-		mds = realloc(mds, sizeof(*mds) * (fd + 1));
-		if (!mds)
+		struct mainloop_data **mds_tmp =
+			realloc(mds, sizeof(*mds) * (fd + 1));
+		if (!mds_tmp) {
+			free(mds);
 			return -1;
+		}
+		mds = mds_tmp;
 		nrhandler = fd + 1;
 	}
 

2.25.1

Hi Kuan-Wei,

Thanks for reporting the issue and proposing the fix.

The description is not accurate actually, neither the fix.

What is happening is we are losing the pointer information as the 'mds' variable is a global variable. So the assignation will overwrite the current pointer if it fails. That leads to a NULL pointer dereference in the mainloop_del.

Looking closer to the code, it seems 'mds' is not used as the stored information is not accessed.

For my understanding, we can just remove the:

static struct mainloop_data **mds

and

static unsigned short nrhandler;

along with the associated code

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In the previous code, the 'mds' and 'nrhandler' variables were not utilized in the codebase. Additionally, there was a potential NULL pointer dereference and memory leak due to improper handling of memory reallocation failure.

This patch removes the unused 'mds' and 'nrhandler' variables along with the associated code, addressing the unused variable issue, NULL pointer dereference issue and the memory leak issue.

---
Changes since v1:
* Remove the unused 'mds' and 'nrhandler' variables along with the associated code.

 tools/thermal/lib/mainloop.c | 16 ----------------
 1 file changed, 16 deletions(-)

index 94cbbcbd1c14..bf4c1b730d7b 100644
@@ -9,7 +9,6 @@
 #include "log.h"
 
 static int epfd = -1;
-static unsigned short nrhandler;
 static sig_atomic_t exit_mainloop;
 
 struct mainloop_data {

@@ -18,8 +17,6 @@ struct mainloop_data {
 	int fd;
 };
 
-static struct mainloop_data **mds;
-
 #define MAX_EVENTS 10
 
 int mainloop(unsigned int timeout)

@@ -61,13 +58,6 @@ int mainloop_add(int fd, mainloop_callback_t cb, void *data)
 
 	struct mainloop_data *md;
 
-	if (fd >= nrhandler) {
-		mds = realloc(mds, sizeof(*mds) * (fd + 1));
-		if (!mds)
-			return -1;
-		nrhandler = fd + 1;
-	}
-
 	md = malloc(sizeof(*md));
 	if (!md)
 		return -1;

@@ -76,7 +66,6 @@ int mainloop_add(int fd, mainloop_callback_t cb, void *data)
 	md->cb = cb;
 	md->fd = fd;
 
-	mds[fd] = md;
 	ev.data.ptr = md;
 
 	if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev) < 0) {

@@ -89,14 +78,9 @@ int mainloop_add(int fd, mainloop_callback_t cb, void *data)
 
 int mainloop_del(int fd)
 {
-	if (fd >= nrhandler)
-		return -1;
-
 	if (epoll_ctl(epfd, EPOLL_CTL_DEL, fd, NULL) < 0)
 		return -1;
 
-	free(mds[fd]);
-
 	return 0;
 }
 

2.25.1

Applied, thanks

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