Affected: Linux

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

udp: Fix memory accounting leak.

Matt Dowling reported a weird UDP memory usage issue.

Under normal operation, the UDP memory usage reported in /proc/net/sockstat remains close to zero. However, it occasionally spiked to 524,288 pages and never dropped. Moreover, the value doubled when the application was terminated. Finally, it caused intermittent packet drops.

We can reproduce the issue with the script below [0]:

1. /proc/net/sockstat reports 0 pages

# cat /proc/net/sockstat | grep UDP: UDP: inuse 1 mem 0

2. Run the script till the report reaches 524,288

# python3 test.py & sleep 5 # cat /proc/net/sockstat | grep UDP: UDP: inuse 3 mem 524288 <-- (INT_MAX + 1) >> PAGE_SHIFT

3. Kill the socket and confirm the number never drops

# pkill python3 && sleep 5 # cat /proc/net/sockstat | grep UDP: UDP: inuse 1 mem 524288

4. (necessary since v6.0) Trigger proto_memory_pcpu_drain()

# python3 test.py & sleep 1 && pkill python3

5. The number doubles

# cat /proc/net/sockstat | grep UDP: UDP: inuse 1 mem 1048577

The application set INT_MAX to SO_RCVBUF, which triggered an integer overflow in udp_rmem_release().

When a socket is close()d, udp_destruct_common() purges its receive queue and sums up skb->truesize in the queue. This total is calculated and stored in a local unsigned integer variable.

The total size is then passed to udp_rmem_release()…