CVE-2026-31498Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop

Official description

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop l2cap_config_req() processes CONFIG_REQ for channels in BT_CONNECTED state to support L2CAP reconfiguration (e.g. MTU changes). However, since both CONF_INPUT_DONE and CONF_OUTPUT_DONE are already set from the initial configuration, the reconfiguration path falls through to l2cap_ertm_init(), which re-initializes tx_q, srej_q, srej_list, and retrans_list without freeing the previous allocations and sets chan->sdu to NULL without freeing the existing skb. This leaks all previously allocated ERTM resources. Additionally, l2cap_parse_conf_req() does not validate the minimum value of remote_mps derived from the RFC max_pdu_size option. A zero value propagates to l2cap_segment_sdu() where pdu_len becomes zero, causing the while loop to never terminate since len is never decremented, exhausting all available memory. Fix the double-init by skipping l2cap_ertm_init() and l2cap_chan_ready() when the channel is already in BT_CONNECTED state, while still allowing the reconfiguration parameters to be updated through l2cap_parse_conf_req(). Also add a pdu_len zero check in l2cap_segment_sdu() as a safeguard.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9760b83cfd24b38caee663f429011a0dd6064fa9
• https://git.kernel.org/stable/c/de37e2655b7abc3f59254c6b72256840f39fc6d5
• https://git.kernel.org/stable/c/e7aab23b7df89a3d754a5f0a7d2237548b328bd0
• https://git.kernel.org/stable/c/52667c859fe33f70c2e711cb81bbd505d5eb8e75
• https://git.kernel.org/stable/c/9a21a631ee034b1573dce14b572a24943dbfd7ae
• https://git.kernel.org/stable/c/900e4db5385ec2cacd372345a80ab9c8e105b3a3
• https://git.kernel.org/stable/c/042e2cd4bb11e5313b19b87593616524949e4c52
• https://git.kernel.org/stable/c/25f420a0d4cfd61d3d23ec4b9c56d9f443d91377