UBUNTU-CVE-2026-98289: Medium severity ubuntu/linux-hwe-edge vulnerability

In the Linux kernel, the following vulnerability has been resolved: afunix: Unify sccindex when finalising SCC in unixwalkscc(). Commit bfdb01283ee8 ("afunix: Assign a unique index to SCC.") changed Tarjan's algorithm to update lowlink with lowlink, which is called lowpoint (unixvertex.sccindex). unixvertexdead() assumes all vertices in an SCC share the same lowpoint, but this is not always true if an SCC has two or more back edges, depending on the order of DFS. For example, the graph below has two back edges from B to A and from C to B. A --> B --> C ^ | ^ | ----' ----' If DFS walks through A -> B -> C -> B (-> C -> B) -> A (-> B -> A), each index and sccindex will be updated as follows. A --> B --> C C = (3, 3) (index, sccindex) B = (2, 2) A = (1, 1) A ... B ... C C = (3, 2)<-. ^ | B = (2, 2) -' ----' A = (1, 1) A ... B ... C C = (3, 2) ^ | . . B = (2, 1)<-. ----' .... A = (1, 1) -' Then, unixvertexdead() thinks that B is passed to another SCC with sccindex 2, and the SCC is not garbage-collected. This does not happen if DFS walks in a different order below or starts from B. 1 3 A --> B --> C ^ | ^ | ----' ----' 2 4 Let's unify sccindex across the SCC when finalising it. Note that updating v->index was previously done in unixsccdead(), when called from unixwalkscc(), just to save one loop. Since unixwalkscc() now iterates over the SCC anyway, the update is moved back to unixwalkscc() and 'fast' argument is dropped.