In the Linux kernel, the following vulnerability has been resolved:
net/9p: fix infinite loop in p9_client_rpc on fatal signal
When p9_client_rpc() is called with type P9_TFLUSH and the transport
has no peer (e.g. fd transport backed by pipes with no 9p server),
a fatal signal causes an infinite loop:
again:
err = io_wait_event_killable(req->wq, ...)
/* SIGKILL wakes the task, returns -ERESTARTSYS */
if (err == -ERESTARTSYS && c->status == Connected &&
type == P9_TFLUSH) {
sigpending = 1;
clear_thread_flag(TIF_SIGPENDING);
goto again;
}
clear_thread_flag() clears TIF_SIGPENDING before jumping back to
io_wait_event_killable(). signal_pending_state() checks TIF_SIGPENDING,
finds it zero, and the task goes to sleep again. The task can only wake
on the next signal delivery that calls signal_wake_up() and sets
TIF_SIGPENDING again. When that happens the loop repeats, clears
TIF_SIGPENDING, and sleeps again indefinitely.
This is triggered in practice by coredump_wait(): when a thread in a
multi-threaded process causes a coredump (e.g. via SIGSYS from Syscall
User Dispatch), coredump_wait() sends SIGKILL to all other threads and
waits for them to call mm_release(). If one of those threads is blocked
in p9_client_rpc() over an fd transport with no peer, it enters the
P9_TFLUSH loop and never calls mm_release(), so coredump_wait() stalls
forever:
INFO: task syz.0.18:676 blocked for more than 143 seconds.
Not tainted 6.12.77+ #1
task:syz.0.18 state:D stack:27600 pid:676 tgid:673 ppid:630 flags:0x00000004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5344 [inline]
__schedule+0xcb4/0x5d50 kernel/sched/core.c:6724
__schedule_loop kernel/sched/core.c:6801 [inline]
schedule+0xe5/0x350 kernel/sched/core.c:6816
schedule_timeout+0x253/0x290 kernel/time/timer.c:2593
do_wait_for_common kernel/sched/completion.c:95 [inline]
__wait_for_common+0x409/0x600 kernel/sched/completion.c:116
wait_for_common kernel/sched/completion.c:127 [inline]
wait_for_completion_state+0x1d/0x40 kernel/sched/completion.c:264
coredump_wait fs/coredump.c:448 [inline]
do_coredump+0x854/0x4350 fs/coredump.c:629
get_signal+0x1425/0x2730 kernel/signal.c:2903
arch_do_signal_or_restart+0x81/0x880 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0xf9/0x160 kernel/entry/common.c:218
do_syscall_64+0x102/0x220 arch/x86/entry/common.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>
Fix: check fatal_signal_pending() before clearing TIF_SIGPENDING in the
P9_TFLUSH retry loop. At that point TIF_SIGPENDING is still set, so
fatal_signal_pending() works correctly. If a fatal signal is pending,
jump to recalc_sigpending to restore TIF_SIGPENDING and return
-ERESTARTSYS to the caller.
The same defect is present in stable kernels back to 5.4. On those
kernels the infinite loop is broken earlier by a second SIGKILL from
the parent process (e.g. kill_and_wait() retrying after a timeout),
resulting in a zombie process and a shutdown delay rather than a
permanent D-state hang, but the underlying flaw is the same.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
net/9p: fix infinite loop in p9_client_rpc on fatal signal
When p9_client_rpc() is called with type P9_TFLUSH and the transport
has no peer (e.g. fd transport backed by pipes with no 9p server),
a fatal signal causes an infinite loop:
again:
err = io_wait_event_killable(req->wq, ...)
/* SIGKILL wakes the task, returns -ERESTARTSYS */
if (err == -ERESTARTSYS && c->status == Connected &&
type == P9_TFLUSH) {
sigpending = 1;
clear_thread_flag(TIF_SIGPENDING);
goto again;
}
clear_thread_flag() clears TIF_SIGPENDING before jumping back to
io_wait_event_killable(). signal_pending_state() checks TIF_SIGPENDING,
finds it zero, and the task goes to sleep again. The task can only wake
on the next signal delivery that calls signal_wake_up() and sets
TIF_SIGPENDING again. When that happens the loop repeats, clears
TIF_SIGPENDING, and sleeps again indefinitely.
This is triggered in practice by coredump_wait(): when a thread in a
multi-threaded process causes a coredump (e.g. via SIGSYS from Syscall
User Dispatch), coredump_wait() sends SIGKILL to all other threads and
waits for them to call mm_release(). If one of those threads is blocked
in p9_client_rpc() over an fd transport with no peer, it enters the
P9_TFLUSH loop and never calls mm_release(), so coredump_wait() stalls
forever:
INFO: task syz.0.18:676 blocked for more than 143 seconds.
Not tainted 6.12.77+ #1
task:syz.0.18 state:D stack:27600 pid:676 tgid:673 ppid:630 flags:0x00000004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5344 [inline]
__schedule+0xcb4/0x5d50 kernel/sched/core.c:6724
__schedule_loop kernel/sched/core.c:6801 [inline]
schedule+0xe5/0x350 kernel/sched/core.c:6816
schedule_timeout+0x253/0x290 kernel/time/timer.c:2593
do_wait_for_common kernel/sched/completion.c:95 [inline]
__wait_for_common+0x409/0x600 kernel/sched/completion.c:116
wait_for_common kernel/sched/completion.c:127 [inline]
wait_for_completion_state+0x1d/0x40 kernel/sched/completion.c:264
coredump_wait fs/coredump.c:448 [inline]
do_coredump+0x854/0x4350 fs/coredump.c:629
get_signal+0x1425/0x2730 kernel/signal.c:2903
arch_do_signal_or_restart+0x81/0x880 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0xf9/0x160 kernel/entry/common.c:218
do_syscall_64+0x102/0x220 arch/x86/entry/common.c:84
entry_SYSCALL_64_after_hwframe+0x77/0x7f
</TASK>
Fix: check fatal_signal_pending() before clearing TIF_SIGPENDING in the
P9_TFLUSH retry loop. At that point TIF_SIGPENDING is still set, so
fatal_signal_pending() works correctly. If a fatal signal is pending,
jump to recalc_sigpending to restore TIF_SIGPENDING and return
-ERESTARTSYS to the caller.
The same defect is present in stable kernels back to 5.4. On those
kernels the infinite loop is broken earlier by a second SIGKILL from
the parent process (e.g. kill_and_wait() retrying after a timeout),
resulting in a zombie process and a shutdown delay rather than a
permanent D-state hang, but the underlying flaw is the same.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Metrics
Affected Vendors & Products
Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Sat, 15 Aug 2026 06:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: net/9p: fix infinite loop in p9_client_rpc on fatal signal When p9_client_rpc() is called with type P9_TFLUSH and the transport has no peer (e.g. fd transport backed by pipes with no 9p server), a fatal signal causes an infinite loop: again: err = io_wait_event_killable(req->wq, ...) /* SIGKILL wakes the task, returns -ERESTARTSYS */ if (err == -ERESTARTSYS && c->status == Connected && type == P9_TFLUSH) { sigpending = 1; clear_thread_flag(TIF_SIGPENDING); goto again; } clear_thread_flag() clears TIF_SIGPENDING before jumping back to io_wait_event_killable(). signal_pending_state() checks TIF_SIGPENDING, finds it zero, and the task goes to sleep again. The task can only wake on the next signal delivery that calls signal_wake_up() and sets TIF_SIGPENDING again. When that happens the loop repeats, clears TIF_SIGPENDING, and sleeps again indefinitely. This is triggered in practice by coredump_wait(): when a thread in a multi-threaded process causes a coredump (e.g. via SIGSYS from Syscall User Dispatch), coredump_wait() sends SIGKILL to all other threads and waits for them to call mm_release(). If one of those threads is blocked in p9_client_rpc() over an fd transport with no peer, it enters the P9_TFLUSH loop and never calls mm_release(), so coredump_wait() stalls forever: INFO: task syz.0.18:676 blocked for more than 143 seconds. Not tainted 6.12.77+ #1 task:syz.0.18 state:D stack:27600 pid:676 tgid:673 ppid:630 flags:0x00000004 Call Trace: <TASK> context_switch kernel/sched/core.c:5344 [inline] __schedule+0xcb4/0x5d50 kernel/sched/core.c:6724 __schedule_loop kernel/sched/core.c:6801 [inline] schedule+0xe5/0x350 kernel/sched/core.c:6816 schedule_timeout+0x253/0x290 kernel/time/timer.c:2593 do_wait_for_common kernel/sched/completion.c:95 [inline] __wait_for_common+0x409/0x600 kernel/sched/completion.c:116 wait_for_common kernel/sched/completion.c:127 [inline] wait_for_completion_state+0x1d/0x40 kernel/sched/completion.c:264 coredump_wait fs/coredump.c:448 [inline] do_coredump+0x854/0x4350 fs/coredump.c:629 get_signal+0x1425/0x2730 kernel/signal.c:2903 arch_do_signal_or_restart+0x81/0x880 arch/x86/kernel/signal.c:337 exit_to_user_mode_loop kernel/entry/common.c:111 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline] __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0xf9/0x160 kernel/entry/common.c:218 do_syscall_64+0x102/0x220 arch/x86/entry/common.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> Fix: check fatal_signal_pending() before clearing TIF_SIGPENDING in the P9_TFLUSH retry loop. At that point TIF_SIGPENDING is still set, so fatal_signal_pending() works correctly. If a fatal signal is pending, jump to recalc_sigpending to restore TIF_SIGPENDING and return -ERESTARTSYS to the caller. The same defect is present in stable kernels back to 5.4. On those kernels the infinite loop is broken earlier by a second SIGKILL from the parent process (e.g. kill_and_wait() retrying after a timeout), resulting in a zombie process and a shutdown delay rather than a permanent D-state hang, but the underlying flaw is the same. Found by Linux Verification Center (linuxtesting.org) with Syzkaller. | |
| Title | net/9p: fix infinite loop in p9_client_rpc on fatal signal | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-08-15T05:53:33.383Z
Reserved: 2026-08-09T03:40:39.909Z
Link: CVE-2026-72166
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-15T06:21:34.620
Modified: 2026-08-15T06:21:34.620
Link: CVE-2026-72166
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.