Bug 2460629 (CVE-2026-31498)

Summary: CVE-2026-31498 kernel: Bluetooth: L2CAP: Fix ERTM re-init and zero pdu_len infinite loop
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Bluetooth L2CAP (Logical Link Control and Adaptation Protocol) implementation. A remote attacker could exploit this by sending a malformed configuration request with a zero-valued maximum PDU (Protocol Data Unit) size. This could lead to an infinite loop, exhausting system memory and causing a denial of service. Additionally, improper handling of channel reconfiguration could result in memory leaks.
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Description OSIDB Bzimport 2026-04-22 15:01:58 UTC 
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.
Comment 1 Keith Grant 2026-04-22 19:16:51 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042204-CVE-2026-31498-1aee@gregkh/T