net/sched: cls_flower: validate mask pointer after nla_next()

Overview

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

net/sched: cls_flower: validate mask pointer after nla_next()

fl_set_enc_opt() iterates the key's nested tunnel-option attributes with nla_for_each_attr() while advancing a single mask pointer via nla_next() at the bottom of each loop, so the mask cursor is driven by the number of key attributes rather than by the mask's own attributes. The nla_ok() added by commit c96adff956191 ("cls_flower: call nla_ok() before nla_next()") only validates the mask pointer that was just consumed; the pointer produced by nla_next() is used by the next iteration (fl_set_geneve_opt() and siblings) without any validation.

The mask's nested attributes are validated with NL_VALIDATE_LIBERAL, which merely warns on trailing bytes that do not form a complete attribute. A mask carrying one valid attribute plus 1-3 residue bytes (or a non-aligned attribute length making msk_depth negative) therefore reaches the next iteration with msk_depth != 0, so neither the !msk_depth check in fl_set_enc_opt() nor the !depth check in the per-type helpers fires. nla_type() then reads past the mask payload and nla_parse_nested_deprecated() iterates with an nla_len taken from those bytes, reading well beyond the mask attribute (KASAN: slab-out-of-bounds read in __nla_validate_parse from fl_change()).

Validate the advanced mask pointer as well: when the mask is not legitimately exhausted (msk_depth != 0) and the new pointer fails nla_ok(), reject the filter with -EINVAL. An exactly exhausted mask still skips the check, preserving exact-match behaviour for the remaining key attributes.

Affected

• Linux >= 238b5ebdb6a6e4bc90810b9f8ec0063b3dfda41a < a9283d006eef7e3b56f0f279a49bb63f6e5e61df
• Linux >= c96adff95619178e2118925578343ad54857c80c < 497944d534ffb1be300365523030c7c6517cbbb6
• Linux >= c96adff95619178e2118925578343ad54857c80c < a55d84907337580d91c0d54779d9d4b934633158
• Linux >= c96adff95619178e2118925578343ad54857c80c < cff9bf34afde46c238189cc6f7690b7e35225df1
• Linux >= c96adff95619178e2118925578343ad54857c80c < 35354bf67aa0f7bace66ffb614906124ed50d59d
• Linux >= c96adff95619178e2118925578343ad54857c80c < 45e60747a9db2307929260d9aa9c1c6cbb70ee77
• Linux >= c96adff95619178e2118925578343ad54857c80c < bb187146c7e5c666874784e4f3fc1bc5126e6e92
• Linux >= c96adff95619178e2118925578343ad54857c80c < fee10655709c5c597e8e9f722f3035d9ea31ff3a
• Linux >= 5.10.11 < 5.10.273
• Linux 5.11

Remediation

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