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

Summary

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.

Timeline

1. Apr 22, 2026, 1:54 PM UTCCVE published
2. May 23, 2026, 4:05 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 4.4.238 · fixed in 4.5; From 4.9.238 · fixed in 4.10; From 4.14.200 · fixed in 4.15; From 4.19.149 · fixed in 4.20; From 5.4.69 · fixed in 5.5

• Linux Linux

  5.7

References 8