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KCSAN: data-race in rds_poll / rds_sendmsg

Status: upstream: reported on 2026/05/21 22:56
Subsystems: rds
Labels: race:harmful prio:low
[Documentation on labels]
Reported-by: syzbot+fbf3648ae7f5bdb05c59@syzkaller.appspotmail.com
Fix commit: rds: annotate data-race around rs_seen_congestion
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce ci-upstream-rust-kasan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 27d, last: 27d
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
21eaa913-9047-45de-8e57-3998dcfb3830 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KCSAN: data-race in rds_poll / rds_sendmsg 2026/06/01 17:14 2026/06/01 17:14 2026/06/01 17:51 386cc6dacdf7e3ebce9507beed6755d7e999554d
89641d0d-2cfe-4d73-a8c7-dfa8ec66a97e assessment-kcsan Benign: ❌ ❓ KCSAN: data-race in rds_poll / rds_sendmsg 2026/05/17 22:58 2026/05/17 22:58 2026/05/17 23:27 de5aae85e5f28e2fa1c7deefcc24fe286abe5140
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH net] rds: annotate data-race around rs_seen_congestion 3 (3) 2026/05/25 19:10
[syzbot] [rds?] KCSAN: data-race in rds_poll / rds_sendmsg 0 (1) 2026/05/21 22:56

Sample crash report:
==================================================================
BUG: KCSAN: data-race in rds_poll / rds_sendmsg

write to 0xffff8881054183a4 of 4 bytes by task 9010 on cpu 0:
 rds_sendmsg+0x1001/0x15b0 net/rds/send.c:1391
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x563/0x5b0 net/socket.c:2698
 ___sys_sendmsg+0x195/0x1e0 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0xd4/0x160 net/socket.c:2787
 x64_sys_call+0x194c/0x3020 arch/x86/include/generated/asm/syscalls_64.h:47
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881054183a4 of 4 bytes by task 9013 on cpu 1:
 rds_poll+0x9b/0x310 net/rds/af_rds.c:222
 sock_poll+0x21c/0x240 net/socket.c:1502
 vfs_poll include/linux/poll.h:82 [inline]
 __io_arm_poll_handler+0x1ef/0xbf0 io_uring/poll.c:590
 io_arm_apoll+0x2eb/0x400 io_uring/poll.c:698
 io_arm_poll_handler+0x12f/0x160 io_uring/poll.c:727
 io_queue_async+0x25d/0x320 io_uring/io_uring.c:1634
 io_queue_sqe io_uring/io_uring.c:1660 [inline]
 io_req_task_submit+0x9b/0xa0 io_uring/io_uring.c:1062
 io_handle_tw_list+0x1f5/0x230 io_uring/tw.c:72
 tctx_task_work_run+0x42/0x140 io_uring/tw.c:132
 tctx_task_work+0x3f/0x80 io_uring/tw.c:150
 task_work_run+0x130/0x1a0 kernel/task_work.c:233
 get_signal+0xdea/0xf20 kernel/signal.c:2809
 arch_do_signal_or_restart+0x96/0x480 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0x6f/0x820 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x232/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 9013 Comm: syz.7.10555 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/17 22:49 upstream e5d505e3664b de5aae85 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in rds_poll / rds_sendmsg
* Struck through repros no longer work on HEAD.