net/packet: prevent TX_RING byte count overflow

Overview

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

net/packet: prevent TX_RING byte count overflow

tpacket_snd() drains every SEND_REQUEST frame in a TX ring and adds each valid packet length to the signed int len_sum. Userspace can recycle completed frames concurrently, so a single blocking send call is not bounded by the ring size.

After enough successful transmissions len_sum wraps into the negative range. In particular, 65536 65535-byte frames followed by a 65007-byte frame produce 0xfffffdef, or -EIOCBQUEUED. sock_sendmsg_nosec() treats that as an impossible return and triggers a BUG. On systems configured to panic on oops, a CAP_NET_RAW holder can panic the host kernel.

Stop before the next frame would make the byte count exceed INT_MAX. The positive short count leaves that frame pending for a later send call.

A two-thread TPACKET_V2 reproducer triggered the BUG on an arm64 build of Linux 7.3-rc4. With this change, the same reproducer returned the expected positive short count without an oops.

Affected

• Linux >= 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 < be12b221c0301111eeb023be04add3c6ad7c21fe
• Linux >= 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 < 69ca64bbb528898916f309552053c32a04a36ebc
• Linux >= 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 < 9fd63d284e251332f4874ef9023cde472f315f86
• Linux >= 69e3c75f4d541a6eb151b3ef91f34033cb3ad6e1 < 2cf81fc9505b148b1b70068303ea6ea4b1212403
• Linux 2.6.31

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.