CVE-2025-21792: ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt
Description
In the Linux kernel, the following vulnerability has been resolved:
ax25: Fix refcount leak caused by setting SO_BINDTODEVICE sockopt
If an AX25 device is bound to a socket by setting the SO_BINDTODEVICE
socket option, a refcount leak will occur in ax25_release().
Commit 9fd75b66b8f6 ("ax25: Fix refcount leaks caused by ax25_cb_del()")
added decrement of device refcounts in ax25_release(). In order for that
to work correctly the refcounts must already be incremented when the
device is bound to the socket. An AX25 device can be bound to a socket
by either calling ax25_bind() or setting SO_BINDTODEVICE socket option.
In both cases the refcounts should be incremented, but in fact it is done
only in ax25_bind().
This bug leads to the following issue reported by Syzkaller:
================================================================
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 1 PID: 5932 at lib/refcount.c:31 refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31
Modules linked in:
CPU: 1 UID: 0 PID: 5932 Comm: syz-executor424 Not tainted 6.13.0-rc4-syzkaller-00110-g4099a71718b0 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x1ed/0x210 lib/refcount.c:31
Call Trace:
__refcount_dec include/linux/refcount.h:336 [inline]
refcount_dec include/linux/refcount.h:351 [inline]
ref_tracker_free+0x710/0x820 lib/ref_tracker.c:236
netdev_tracker_free include/linux/netdevice.h:4...
Classification
CVE ID: CVE-2025-21792
Affected Products
Vendor: Linux, Linux
Product: Linux, Linux
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.02% (probability of being exploited)
EPSS Percentile: 1.72% (scored less or equal to compared to others)
EPSS Date: 2025-03-27 (when was this score calculated)
References
https://nvd.nist.gov/vuln/detail/CVE-2025-21792https://git.kernel.org/stable/c/90056ece99966182dc0e367f3fd2afab46ada847
https://git.kernel.org/stable/c/94a0de224ed52eb2ecd4f4cb1b937b674c9fb955
https://git.kernel.org/stable/c/b58f7ca86a7b8e480c06e30c5163c5d2f4e24023
https://git.kernel.org/stable/c/470bda72fda0fcf54300466d70ce2de62f7835d2
https://git.kernel.org/stable/c/bca0902e61731a75fc4860c8720168d9f1bae3b6