{"id":"CVE-2026-80819","summary":"Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept","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":"2026-09-06T03:46:51.458853102Z","published":"2026-09-04T15:13:40.309Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80819.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/355bfd57ca4ca881c6eb03ca813b440a094b1f44"},{"type":"WEB","url":"https://git.kernel.org/stable/c/362726c9c6e56eea4262109183e49868c39ccd3a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/43a556b2fd43f2df6dded59c2e26560a27874c24"},{"type":"WEB","url":"https://git.kernel.org/stable/c/56f0aa75c7640e46397ef73bea251fcbef9150c0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/825b95561d7b7c393df9e7bc295451aaeadc3d18"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b405c2f96ae2e37375105881890f7738833b1d62"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d4b1a13b1eff2e80925c7368ffdeaaa50cba93df"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d8d686dd5662a7c4745e4515f1237a9f3b7df181"},{"type":"WEB","url":"https://git.kernel.org/stable/c/eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80819.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80819"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"bb23c0ab824653be4aa7dfca15b07b3059717004"},{"fixed":"d8d686dd5662a7c4745e4515f1237a9f3b7df181"},{"fixed":"eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2"},{"fixed":"56f0aa75c7640e46397ef73bea251fcbef9150c0"},{"fixed":"362726c9c6e56eea4262109183e49868c39ccd3a"},{"fixed":"825b95561d7b7c393df9e7bc295451aaeadc3d18"},{"fixed":"d4b1a13b1eff2e80925c7368ffdeaaa50cba93df"},{"fixed":"355bfd57ca4ca881c6eb03ca813b440a094b1f44"},{"fixed":"b405c2f96ae2e37375105881890f7738833b1d62"},{"fixed":"43a556b2fd43f2df6dded59c2e26560a27874c24"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80819.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.30"},{"fixed":"5.10.267"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.218"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.185"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.154"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.106"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.47"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.11"}]},{"type":"ECOSYSTEM","events":[{"introduced":"7.2.0"},{"fixed":"7.2.1"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80819.json"}}],"schema_version":"1.9.0"}