CVE-2021-47556

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

ethtool: ioctl: fix potential NULL deref in ethtool_set_coalesce()

ethtool_set_coalesce() now uses both the .get_coalesce() and .set_coalesce() callbacks. But the check for their availability is buggy, so changing the coalesce settings on a device where the driver provides only one of the callbacks results in a NULL pointer dereference instead of an -EOPNOTSUPP.

Fix the condition so that the availability of both callbacks is ensured. This also matches the netlink code.

Note that reproducing this requires some effort - it only affects the legacy ioctl path, and needs a specific combination of driver options:

• have .get_coalesce() and .coalesce_supported but no .set_coalesce(), or
• have .set_coalesce() but no .get_coalesce(). Here eg. ethtool doesnt cause the crash as it first attempts to call ethtool_get_coalesce() and bails out on error.

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0276af2176c78771da7f311621a25d7608045827
• https://git.kernel.org/stable/c/abfdd9e2f0f9699015d72317f74154d3e53664e6