Patch "ax25: Fix reference count leak issues of ax25_dev" has been added to the 6.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ax25: Fix reference count leak issues of ax25_dev

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ax25-fix-reference-count-leak-issues-of-ax25_dev.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a4a479e06ebe4332a67d15bddc2e05297ba340ce
Author: Duoming Zhou <duoming@xxxxxxxxxx>
Date:   Thu May 9 17:36:47 2024 +0800

    ax25: Fix reference count leak issues of ax25_dev
    
    [ Upstream commit b505e0319852b08a3a716b64620168eab21f4ced ]
    
    The ax25_addr_ax25dev() and ax25_dev_device_down() exist a reference
    count leak issue of the object "ax25_dev".
    
    Memory leak issue in ax25_addr_ax25dev():
    
    The reference count of the object "ax25_dev" can be increased multiple
    times in ax25_addr_ax25dev(). This will cause a memory leak.
    
    Memory leak issues in ax25_dev_device_down():
    
    The reference count of ax25_dev is set to 1 in ax25_dev_device_up() and
    then increase the reference count when ax25_dev is added to ax25_dev_list.
    As a result, the reference count of ax25_dev is 2. But when the device is
    shutting down. The ax25_dev_device_down() drops the reference count once
    or twice depending on if we goto unlock_put or not, which will cause
    memory leak.
    
    As for the issue of ax25_addr_ax25dev(), it is impossible for one pointer
    to be on a list twice. So add a break in ax25_addr_ax25dev(). As for the
    issue of ax25_dev_device_down(), increase the reference count of ax25_dev
    once in ax25_dev_device_up() and decrease the reference count of ax25_dev
    after it is removed from the ax25_dev_list.
    
    Fixes: d01ffb9eee4a ("ax25: add refcount in ax25_dev to avoid UAF bugs")
    Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
    Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
    Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/361bbf2a4b091e120006279ec3b382d73c4a0c17.1715247018.git.duoming@xxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ax25/ax25_dev.c b/net/ax25/ax25_dev.c
index f16ee5c09d07a..52ccc37d5687a 100644
--- a/net/ax25/ax25_dev.c
+++ b/net/ax25/ax25_dev.c
@@ -39,6 +39,7 @@ ax25_dev *ax25_addr_ax25dev(ax25_address *addr)
 		if (ax25cmp(addr, (const ax25_address *)ax25_dev->dev->dev_addr) == 0) {
 			res = ax25_dev;
 			ax25_dev_hold(ax25_dev);
+			break;
 		}
 	spin_unlock_bh(&ax25_dev_lock);
 
@@ -88,7 +89,6 @@ void ax25_dev_device_up(struct net_device *dev)
 	list_add(&ax25_dev->list, &ax25_dev_list);
 	dev->ax25_ptr     = ax25_dev;
 	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_hold(ax25_dev);
 
 	ax25_register_dev_sysctl(ax25_dev);
 }
@@ -129,7 +129,6 @@ void ax25_dev_device_down(struct net_device *dev)
 unlock_put:
 	dev->ax25_ptr = NULL;
 	spin_unlock_bh(&ax25_dev_lock);
-	ax25_dev_put(ax25_dev);
 	netdev_put(dev, &ax25_dev->dev_tracker);
 	ax25_dev_put(ax25_dev);
 }