Vulnerability CVE-2024-26826
Published: 2024-04-17

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

mptcp: fix data re-injection from stale subflow

When the MPTCP PM detects that a subflow is stale, all the packet
scheduler must re-inject all the mptcp-level unacked data. To avoid
acquiring unneeded locks, it first try to check if any unacked data
is present at all in the RTX queue, but such check is currently
broken, as it uses TCP-specific helper on an MPTCP socket.

Funnily enough fuzzers and static checkers are happy, as the accessed
memory still belongs to the mptcp_sock struct, and even from a
functional perspective the recovery completed successfully, as
the short-cut test always failed.

A recent unrelated TCP change - commit d5fed5addb2b ("tcp: reorganize
tcp_sock fast path variables") - exposed the issue, as the tcp field
reorganization makes the mptcp code always skip the re-inection.

Fix the issue dropping the bogus call: we are on a slow path, the early
optimization proved once again to be evil.

 References:
https://git.kernel.org/stable/c/6f95120f898b40d13fd441225ef511307853c9c2
https://git.kernel.org/stable/c/6673d9f1c2cd984390550dbdf7d5ae07b20abbf8
https://git.kernel.org/stable/c/b609c783c535493aa3fca22c7e40a120370b1ca5
https://git.kernel.org/stable/c/624902eab7abcb8731b333ec73f206d38d839cd8
https://git.kernel.org/stable/c/b6c620dc43ccb4e802894e54b651cf81495e9598
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