net: ipconfig: bound DHCP option construction

Overview

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

net: ipconfig: bound DHCP option construction

ic_dhcp_init_options() appends the hostname (option 12), vendor-class (option 60) and client-ID (option 61) options into the fixed 312-byte bootp_pkt.exten[] buffer. Only the client-ID branch checked the remaining space; the hostname and vendor-class writes were unbounded.

A 64-byte hostname together with the maximum 252-byte dhcpclass= identifier needs 18 + (2 + 64) + (2 + 252) = 338 of the 312 available bytes even before the terminating END marker, so the vendor-class memcpy runs past the end of exten[]. With CONFIG_FORTIFY_SOURCE this is reported as a field-spanning write and, when the kernel is booted with panic_on_warn=1, aborts boot with a panic.

Route the optional options through a common helper that makes sure the option, its 2-byte header and the END marker all fit and drops an option that would not. Configurations with short options keep sending exactly the same bytes as before.

Affected

• Linux >= 130c0f47fdf9c533deb1136cad5136f6cb7020f0 < abcba6f080c63e403037ecdffde43170d242376a
• Linux >= 130c0f47fdf9c533deb1136cad5136f6cb7020f0 < 24e79508b237dd2a69bc6fb6ac5cf7f126178307
• Linux >= 130c0f47fdf9c533deb1136cad5136f6cb7020f0 < cbaad2922bd5d4d303055ae9afecc8999e6b40c9
• Linux >= 130c0f47fdf9c533deb1136cad5136f6cb7020f0 < e47a1958e12abc3a17b5231a4f21c8f1bf662e08
• Linux 2.6.36

Remediation

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