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Unrated severityNVD Advisory· Published Jul 12, 2024· Updated Nov 3, 2025

ax25: Fix refcount imbalance on inbound connections

CVE-2024-40910

Description

In the Linux kernel, the following vulnerability has been resolved:

ax25: Fix refcount imbalance on inbound connections

When releasing a socket in ax25_release(), we call netdev_put() to decrease the refcount on the associated ax.25 device. However, the execution path for accepting an incoming connection never calls netdev_hold(). This imbalance leads to refcount errors, and ultimately to kernel crashes.

A typical call trace for the above situation will start with one of the following errors:

refcount_t: decrement hit 0; leaking memory. refcount_t: underflow; use-after-free.

And will then have a trace like:

Call Trace:

? show_regs+0x64/0x70 ? __warn+0x83/0x120 ? refcount_warn_saturate+0xb2/0x100 ? report_bug+0x158/0x190 ? prb_read_valid+0x20/0x30 ? handle_bug+0x3e/0x70 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? refcount_warn_saturate+0xb2/0x100 ? refcount_warn_saturate+0xb2/0x100 ax25_release+0x2ad/0x360 __sock_release+0x35/0xa0 sock_close+0x19/0x20 [...]

On reboot (or any attempt to remove the interface), the kernel gets stuck in an infinite loop:

unregister_netdevice: waiting for ax0 to become free. Usage count = 0

This patch corrects these issues by ensuring that we call netdev_hold() and ax25_dev_hold() for new connections in ax25_accept(). This makes the logic leading to ax25_accept() match the logic for ax25_bind(): in both cases we increment the refcount, which is ultimately decremented in ax25_release().

Affected products

177

Patches

4
3c34fb0bd4a4
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitvia osv
commit
a723a6c8d483
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitvia osv
commit
52100fd74ad0
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitvia osv
commit
f4df9d6c8d4e
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitvia osv
commit

Vulnerability mechanics

Generated on May 9, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.

References

4

News mentions

0

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