{"id":"AZL-99633","summary":"CVE-2026-80819 affecting package kernel 6.6.150.1-1","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nBluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept\n\nrfcomm_sock_recvmsg() completes a deferred setup by calling\nrfcomm_dlc_accept() without holding any RFCOMM lock:\n\n\tif (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d-\u003eflags)) {\n\t\trfcomm_dlc_accept(d);\n\t\treturn 0;\n\t}\n\nand rfcomm_dlc_accept() dereferences the session on its first line:\n\n\tstruct sock *sk = d-\u003esession-\u003esock-\u003esk;\n\nEvery other path that touches d-\u003esession runs under rfcomm_mutex:\nrfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),\nrfcomm_dlc_send_rpn(), and the RFCOMM thread through\nrfcomm_process_sessions(). rfcomm_connect_ind() is even documented as\n\"called under rfcomm_lock()\". This call site is the only one that skips\nit.\n\nThe RFCOMM_DEFER_SETUP bit looks like it serialises the accept against\nteardown, since __rfcomm_dlc_close() returns early when it wins the\ntest_and_clear. But rfcomm_recv_disc() forces the state first:\n\n\td-\u003estate = BT_CLOSED;\n\t__rfcomm_dlc_close(d, err);\n\nand the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and\nBT_CONNECT2. With the state already BT_CLOSED that switch does not\nmatch, the bit is never consulted, and __rfcomm_dlc_close() falls\nthrough to rfcomm_dlc_unlink(), which sets d-\u003esession = NULL.\n\nSo a remote DISC on a deferred dlc clears the session while leaving\nRFCOMM_DEFER_SETUP set. The next recvmsg() then passes the\ntest_and_clear and dereferences a NULL session. No timing window is\nneeded: once the DISC has been processed, the dereference is\nunconditional.\n\nGive rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and\nrfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and\nre-checks the session, around a __rfcomm_dlc_accept() that the two\nin-core callers, which already hold the mutex, keep using.\n\nReproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated\nover /dev/vhci: the peer brings up an ACL link, opens L2CAP on the\nRFCOMM PSM, starts a session, opens a dlc on a channel bound with\nBT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on\nthe accepted socket then hits:\n\n  Oops: general protection fault\n  KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]\n  RIP: 0010:rfcomm_dlc_accept+0x54/0x350\n  Call Trace:\n    rfcomm_sock_recvmsg+0x1cd/0x230\n    sock_recvmsg+0x166/0x1c0\n    __sys_recvfrom+0x20d/0x300\n\n0x10 is the offset of sock in struct rfcomm_session. With this patch the\nsame run completes with recv() returning 0 and no report, and lockdep\nstays quiet, confirming rfcomm_mutex is still taken before lock_sock on\nthis path as it is on the thread side.","modified":"2026-09-05T14:17:03.798931698Z","published":"2026-09-04T16:18:09Z","upstream":["CVE-2026-80819"],"references":[{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80819"}],"affected":[{"package":{"name":"kernel","ecosystem":"Azure Linux:3","purl":"pkg:rpm/azure-linux/kernel"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"6.6.150.1-1"}]}],"database_specific":{"source":"https://github.com/microsoft/AzureLinuxVulnerabilityData/blob/main/osv/AZL-99633.json"}}],"schema_version":"1.9.0"}