BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval()

Status: upstream: reported C repro on 2026/09/10 23:12
Reported-by: syzbot+3dd2608c2b40ff211c0d@syzkaller.appspotmail.com
First crash: 7d23h, last: 7d23h
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval() origin:upstream -1 syz, C error 1 72d 577d 0/3 upstream: reported C repro on 2025/02/18 06:45
linux-4.14 BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval() -1 syz, C 3 1306d 1680d 0/1 upstream: reported C repro on 2022/02/11 04:42
upstream BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval() net -1 syz, C inconclusive error 64 472d 1712d 0/29 auto-obsoleted due to no activity on 2025/09/11 13:42
linux-4.19 BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval() -1 syz, C error 14 1307d 1700d 0/1 upstream: reported C repro on 2022/01/22 17:14

Sample crash report:
BUG: "hc->tx_t_ipi == 0" holds (exception!) at net/dccp/ccids/ccid3.c:90/ccid3_update_send_interval()
CPU: 0 PID: 4458 Comm: syz.0.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
Call trace:
 dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 ccid3_update_send_interval net/dccp/ccids/ccid3.c:90 [inline]
 ccid3_hc_tx_update_s net/dccp/ccids/ccid3.c:169 [inline]
 ccid3_hc_tx_packet_sent+0x240/0x2c4 net/dccp/ccids/ccid3.c:353
 ccid_hc_tx_packet_sent net/dccp/ccid.h:175 [inline]
 dccp_xmit_packet+0x298/0x460 net/dccp/output.c:289
 dccp_write_xmit+0x118/0x1d0 net/dccp/output.c:366
 dccp_sendmsg+0x53c/0x8f4 net/dccp/proto.c:798
 inet_sendmsg+0x154/0x27c net/ipv4/af_inet.c:841
 sock_sendmsg_nosec net/socket.c:718 [inline]
 __sock_sendmsg net/socket.c:730 [inline]
 __sys_sendto+0x324/0x440 net/socket.c:2153
 __do_sys_sendto net/socket.c:2165 [inline]
 __se_sys_sendto net/socket.c:2161 [inline]
 __arm64_sys_sendto+0xe4/0x104 net/socket.c:2161
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/10 23:12 linux-6.1.y cf82dcca9634 1fe56c0a .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 BUG: "hc->tx_t_ipi == NUM" holds (exception!) at net/dccp/ccids/ccid3.c:LINE/ccid3_update_send_interval()
* Struck through repros no longer work on HEAD.