rfcomm_tty_set_termios() tests dlc->session without rfcomm_mutex and later passes the pointer to rfcomm_send_rpn(). The latter dereferences both session->initiator and session->sock. Meanwhile, krfcommd can unlink the DLC and free the session while holding rfcomm_mutex. The race can proceed as follows: TTY ioctl task krfcommd -------------- -------- load dlc->session enter rfcomm_send_rpn() lock rfcomm_mutex clear dlc->session free session unlock rfcomm_mutex read session->initiator KASAN reported: BUG: KASAN: slab-use-after-free in rfcomm_send_rpn+0x297/0x2a0 Read of size 4 at addr ffff88810012a850 by task poc/92 Call Trace: rfcomm_send_rpn+0x297/0x2a0 rfcomm_tty_set_termios+0x50d/0x850 tty_set_termios+0x596/0x950 set_termios+0x46a/0x6e0 tty_mode_ioctl+0x152/0xbd0 tty_ioctl+0x915/0x1240 __x64_sys_ioctl+0x134/0x1c0 Allocated by task 92: rfcomm_session_add+0x9e/0x2e0 rfcomm_dlc_open+0x8b1/0xe00 rfcomm_dev_activate+0x85/0x1a0 rfcomm_tty_open+0x90/0x280 Freed by task 68: kfree+0x131/0x3c0 rfcomm_session_del+0x119/0x180 rfcomm_run+0x737/0x4710 Add rfcomm_dlc_send_rpn(), which holds rfcomm_mutex while it verifies that the DLC is still attached and sends the RPN frame. Have the TTY path use the helper and drop its unlocked session check. This keeps the session valid through both the frame construction and socket send.
Unified · Split
| @@ -226,6 +226,9 @@ int rfcomm_send_rpn(struct rfcomm_session *s, int cr, u8 dlci, · 225 unmodified lines | |||
| 226 | u8 bit_rate, u8 data_bits, u8 stop_bits, | 226 | u8 bit_rate, u8 data_bits, u8 stop_bits, |
| 227 | u8 parity, u8 flow_ctrl_settings, | 227 | u8 parity, u8 flow_ctrl_settings, |
| 228 | u8 xon_char, u8 xoff_char, u16 param_mask); | 228 | u8 xon_char, u8 xoff_char, u16 param_mask); |
| 229 | int rfcomm_dlc_send_rpn(struct rfcomm_dlc *d, u8 bit_rate, u8 data_bits, | ||
| 230 | u8 stop_bits, u8 parity, u8 flow_ctrl_settings, | ||
| 231 | u8 xon_char, u8 xoff_char, u16 param_mask); | ||
| 229 | 232 | ||
| 230 | /* ---- RFCOMM DLCs (channels) ---- */ | 233 | /* ---- RFCOMM DLCs (channels) ---- */ |
| 231 | struct rfcomm_dlc *rfcomm_dlc_alloc(gfp_t prio); | 234 | struct rfcomm_dlc *rfcomm_dlc_alloc(gfp_t prio); |
| @@ -1028,6 +1028,23 @@ int rfcomm_send_rpn(struct rfcomm_session *s, int cr, u8 dlci, · 1027 unmodified lines | |||
| 1028 | return rfcomm_send_frame(s, buf, ptr - buf); | 1028 | return rfcomm_send_frame(s, buf, ptr - buf); |
| 1029 | } | 1029 | } |
| 1030 | 1030 | ||
| 1031 | int rfcomm_dlc_send_rpn(struct rfcomm_dlc *d, u8 bit_rate, u8 data_bits, | ||
| 1032 | u8 stop_bits, u8 parity, u8 flow_ctrl_settings, | ||
| 1033 | u8 xon_char, u8 xoff_char, u16 param_mask) | ||
| 1034 | { | ||
| 1035 | int err = -ENOTCONN; | ||
| 1036 | |||
| 1037 | rfcomm_lock(); | ||
| 1038 | if (d->session) | ||
| 1039 | err = rfcomm_send_rpn(d->session, 1, d->dlci, bit_rate, | ||
| 1040 | data_bits, stop_bits, parity, | ||
| 1041 | flow_ctrl_settings, xon_char, xoff_char, | ||
| 1042 | param_mask); | ||
| 1043 | rfcomm_unlock(); | ||
| 1044 | |||
| 1045 | return err; | ||
| 1046 | } | ||
| 1047 | |||
| 1031 | static int rfcomm_send_rls(struct rfcomm_session *s, int cr, u8 dlci, u8 status) | 1048 | static int rfcomm_send_rls(struct rfcomm_session *s, int cr, u8 dlci, u8 status) |
| 1032 | { | 1049 | { |
| 1033 | struct rfcomm_hdr *hdr; | 1050 | struct rfcomm_hdr *hdr; |
| @@ -858,7 +858,7 @@ static void rfcomm_tty_set_termios(struct tty_struct *tty, · 857 unmodified lines | |||
| 858 | 858 | ||
| 859 | BT_DBG("tty %p termios %p", tty, old); | 859 | BT_DBG("tty %p termios %p", tty, old); |
| 860 | 860 | ||
| 861 | if (!dev || !dev->dlc || !dev->dlc->session) | 861 | if (!dev || !dev->dlc) |
| 862 | return; | 862 | return; |
| 863 | 863 | ||
| 864 | /* Handle turning off CRTSCTS */ | 864 | /* Handle turning off CRTSCTS */ |
| @@ -979,9 +979,8 @@ static void rfcomm_tty_set_termios(struct tty_struct *tty, · 114 unmodified lines | |||
| 979 | } | 979 | } |
| 980 | 980 | ||
| 981 | if (changes) | 981 | if (changes) |
| 982 | rfcomm_send_rpn(dev->dlc->session, 1, dev->dlc->dlci, baud, | 982 | rfcomm_dlc_send_rpn(dev->dlc, baud, data_bits, stop_bits, parity, |
| 983 | data_bits, stop_bits, parity, | 983 | RFCOMM_RPN_FLOW_NONE, x_on, x_off, changes); |
| 984 | RFCOMM_RPN_FLOW_NONE, x_on, x_off, changes); | ||
| 985 | } | 984 | } |
| 986 | 985 | ||
| 987 | static void rfcomm_tty_throttle(struct tty_struct *tty) | 986 | static void rfcomm_tty_throttle(struct tty_struct *tty) |