Vulnerability CVE-2024-35960
Published: 2024-05-20

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

net/mlx5: Properly link new fs rules into the tree

Previously, add_rule_fg would only add newly created rules from the
handle into the tree when they had a refcount of 1. On the other hand,
create_flow_handle tries hard to find and reference already existing
identical rules instead of creating new ones.

These two behaviors can result in a situation where create_flow_handle
1) creates a new rule and references it, then
2) in a subsequent step during the same handle creation references it
again,
resulting in a rule with a refcount of 2 that is not linked into the
tree, will have a NULL parent and root and will result in a crash when
the flow group is deleted because del_sw_hw_rule, invoked on rule
deletion, assumes node->parent is != NULL.

This happened in the wild, due to another bug related to incorrect
handling of duplicate pkt_reformat ids, which lead to the code in
create_flow_handle incorrectly referencing a just-added rule in the same
flow handle, resulting in the problem described above. Full details are
at [1].

This patch changes add_rule_fg to add new rules without parents into
the tree, properly initializing them and avoiding the crash. This makes
it more consistent with how rules are added to an FTE in
create_flow_handle.

 References:
https://git.kernel.org/stable/c/de0139719cdda82806a47580ca0df06fc85e0bd2
https://git.kernel.org/stable/c/1263b0b26077b1183c3c45a0a2479573a351d423
https://git.kernel.org/stable/c/3d90ca9145f6b97b38d0c2b6b30f6ca6af9c1801
https://git.kernel.org/stable/c/7aaee12b804c5e0374e7b132b6ec2158ff33dd64
https://git.kernel.org/stable/c/2e8dc5cffc844dacfa79f056dea88002312f253f
https://git.kernel.org/stable/c/5cf5337ef701830f173b4eec00a4f984adeb57a0
https://git.kernel.org/stable/c/adf67a03af39095f05d82050f15813d6f700159d
https://git.kernel.org/stable/c/7c6782ad4911cbee874e85630226ed389ff2e453
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