net: skbuff: fix pull-bound underflow in skb_checksum_setup_ipv6()

Overview

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

net: skbuff: fix pull-bound underflow in skb_checksum_setup_ipv6()

skb_maybe_pull_tail() subtracts skb_headlen(skb) from the unsigned max argument and passes the result to __pskb_pull_tail() as a signed int. The function does not ensure that max is at least skb_headlen(skb).

This can happen while parsing IPv6 extension headers when an skb already has a linear area larger than MAX_IPV6_HDR_LEN. Once the parser needs data beyond the linear area, max - skb_headlen(skb) wraps and is converted to a negative delta. __pskb_pull_tail() then passes that negative length to skb_copy_bits(), where it can become a very large copy length.

Pass the requested length itself as the pull bound at the three extension-header call sites, so the delta can no longer go negative.

Affected

• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < 9c4e432132a97b82edf28fa172c39f743e6bfb26
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < 718747afa5463d9cc5fd9a09f03b2a492edd9b78
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < a0ad0473c09d2e947aecac5c82e637ec85924b12
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < b2da5ed3d8c75e1b729a21b6d3beaed415e263f6
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < 6c28c31f051dbf49c71ba7ab7bb9bc905fa1d14b
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < cfa643f2ca36c6f913fe1a2ceb12412ebb0fd962
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < d7f474226809471dc7877435e9c492cc914df0bf
• Linux >= 1431fb31ecbaba1b5718006128f0f2ed0b94e1c3 < 3b4e0b0c008a8c1b474730248cd5b873026c74bd
• Linux 3.13

Remediation

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