CVE-2021-47013: net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-02-28 · updated 2026-08-04
Weakness: CWE-416

Description

In the Linux kernel, the following vulnerability has been resolved: net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..). If some error happens in emac_tx_fill_tpd(), the skb will be freed via dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd(). But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len). As i observed that emac_tx_fill_tpd() haven't modified the value of skb->len, thus my patch assigns skb->len to 'len' before the possible free and use 'len' instead of skb->len later.

Affected products

Linux kernel: from 4.9 before 4.9.269; from 4.10 before 4.14.233; from 4.15 before 4.19.191; from 4.20 before 5.4.119; from 5.5 before 5.10.37; from 5.11 before 5.11.21 — fixed in 4.14.233, 4.19.191, 4.9.269, 5.10.37, 5.11.21, 5.12.4

How to fix

Upgrade to a fixed version: Linux kernel 4.14.233, 4.19.191, 4.9.269, 5.10.37. Check the vendor advisory for mitigations.

References

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