CVE-2026-90088 — Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

Affected: Linux

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

Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

rfcomm_apply_pn() accepts the MTU value from a remote PN (Parameter Negotiation) frame without checking for zero. When the remote peer sends an MTU of zero, d->mtu is set to 0. This causes the sendmsg path to enter an infinite loop when fragmenting data, as each fragment has size == min_t(size_t, len, 0) == 0, so the remaining length never decreases. The infinite allocation of zero-length skbs exhausts all system memory.

Fix by clamping d->mtu to RFCOMM_DEFAULT_MTU when the negotiated value is zero, consistent with the initial value assigned in rfcomm_dlc_alloc().

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CVE-2026-90088 — Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop