linux-kernel - [PATCH 2/3] misc: fastrpc: Don't remove map on creater_process and device

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Date:   Fri,  2 Sep 2022 18:14:22 +0300
From:   Abel Vesa <abel.vesa@...aro.org>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Ekansh Gupta <ekangupt@....qualcomm.com>,
        Vamsi Krishna Gattupalli <quic_vgattupa@...cinc.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ola Jeppsson <ola@...p.com>
Subject: [PATCH 2/3] misc: fastrpc: Don't remove map on creater_process and device_release

Do not remove the map from the list on error path in
fastrpc_init_create_process, instead call fastrpc_map_put, to avoid
use-after-free. Do not remove it on fastrpc_device_release either,
call fastrpc_map_put instead.

The fastrpc_free_map is the only proper place to remove the map.
This is called only after the reference count is 0.

Fixes: b49f6d83e290f ("misc: fastrpc: Fix a possible double free")
Co-developed-by: Ola Jeppsson <ola@...p.com>
Signed-off-by: Ola Jeppsson <ola@...p.com>
Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
---
 drivers/misc/fastrpc.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index 0c816a11eeec..50c17f5da3a8 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -316,6 +316,13 @@ static void fastrpc_free_map(struct kref *ref)
 		dma_buf_put(map->buf);
 	}
 
+	if (map->fl) {
+		spin_lock(&map->fl->lock);
+		list_del(&map->node);
+		spin_unlock(&map->fl->lock);
+		map->fl = NULL;
+	}
+
 	kfree(map);
 }
 
@@ -1266,12 +1273,7 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
 	fl->init_mem = NULL;
 	fastrpc_buf_free(imem);
 err_alloc:
-	if (map) {
-		spin_lock(&fl->lock);
-		list_del(&map->node);
-		spin_unlock(&fl->lock);
-		fastrpc_map_put(map);
-	}
+	fastrpc_map_put(map);
 err:
 	kfree(args);
 
@@ -1347,10 +1349,8 @@ static int fastrpc_device_release(struct inode *inode, struct file *file)
 		fastrpc_context_put(ctx);
 	}
 
-	list_for_each_entry_safe(map, m, &fl->maps, node) {
-		list_del(&map->node);
+	list_for_each_entry_safe(map, m, &fl->maps, node)
 		fastrpc_map_put(map);
-	}
 
 	list_for_each_entry_safe(buf, b, &fl->mmaps, node) {
 		list_del(&buf->node);
-- 
2.34.1