In the Linux kernel, the following vulnerability has been resolved:
io_uring: Fix a null-ptr-deref in io_tctx_exit_cb()
Syzkaller reports a NULL deref bug as follows:
BUG: KASAN: null-ptr-deref in io_tctx_exit_cb+0x53/0xd3 Read of size 4 at addr 0000000000000138 by task file1/1955
CPU: 1 PID: 1955 Comm: file1 Not tainted 6.1.0-rc7-00103-gef4d3ea40565 #75 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0xcd/0x134 ? io_tctx_exit_cb+0x53/0xd3 kasan_report+0xbb/0x1f0 ? io_tctx_exit_cb+0x53/0xd3 kasan_check_range+0x140/0x190 io_tctx_exit_cb+0x53/0xd3 task_work_run+0x164/0x250 ? task_work_cancel+0x30/0x30 get_signal+0x1c3/0x2440 ? lock_downgrade+0x6e0/0x6e0 ? lock_downgrade+0x6e0/0x6e0 ? exit_signals+0x8b0/0x8b0 ? do_raw_read_unlock+0x3b/0x70 ? do_raw_spin_unlock+0x50/0x230 arch_do_signal_or_restart+0x82/0x2470 ? kmem_cache_free+0x260/0x4b0 ? putname+0xfe/0x140 ? get_sigframe_size+0x10/0x10 ? do_execveat_common.isra.0+0x226/0x710 ? lockdep_hardirqs_on+0x79/0x100 ? putname+0xfe/0x140 ? do_execveat_common.isra.0+0x238/0x710 exit_to_user_mode_prepare+0x15f/0x250 syscall_exit_to_user_mode+0x19/0x50 do_syscall_64+0x42/0xb0 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0023:0x0 Code: Unable to access opcode bytes at 0xffffffffffffffd6. RSP: 002b:00000000fffb7790 EFLAGS: 00000200 ORIG_RAX: 000000000000000b RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 </TASK> Kernel panic - not syncing: panic_on_warn set ...
This happens because the adding of task_work from io_ring_exit_work() isn't synchronized with canceling all work items from eg exec. The execution of the two are ordered in that they are both run by the task itself, but if io_tctx_exit_cb() is queued while we're canceling all work items off exec AND gets executed when the task exits to userspace rather than in the main loop in io_uring_cancel_generic(), then we can find current->io_uring == NULL and hit the above crash.
It's safe to add this NULL check here, because the execution of the two paths are done by the task itself.
[axboe: add code comment and also put an explanation in the commit msg]
CVSS Details
- CVSS 3.1 Base Score: 5.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Amazon Linux Ami 2 | — | Upgrade bpftool-debuginfoUpgrade kernel-debuginfo-common-x86_64Upgrade bpftoolUpgrade python-perf-debuginfoUpgrade kernel-tools-debuginfoUpgrade python-perfUpgrade kernel-toolsUpgrade kernel-debuginfoUpgrade kernel-headersUpgrade kernel-tools-develUpgrade perf-debuginfoUpgrade perfUpgrade kernelUpgrade kernel-livepatch-5.15.86-53.137Upgrade kernel-debuginfo-common-aarch64Upgrade kernel-devel | Mar 14, 2025 | Oct 21, 2024 |
| Debian | — | Upgrade linux | Oct 23, 2024 | Oct 23, 2024 |
| Redhat_linux | — | No solution exists | Jul 9, 2025 | Oct 21, 2024 |
| Ubuntu | — | Upgrade linux-azure-5.15Upgrade linux-gcp-5.15Upgrade linux-gcpUpgrade linuxUpgrade linux-hwe-5.15Upgrade linux-gkeop-5.15Upgrade linux-intel-iot-realtimeUpgrade linux-kvmUpgrade linux-awsUpgrade linux-ibmUpgrade linux-intel-iotg-5.15Upgrade linux-bluefieldUpgrade linux-azureUpgrade linux-aws-5.15Upgrade linux-nvidiaUpgrade linux-gkeUpgrade linux-azure-fdeUpgrade linux-realtimeUpgrade linux-azure-fde-5.15Upgrade linux-riscv-5.15Upgrade linux-lowlatency-hwe-5.15Upgrade linux-oracleUpgrade linux-oracle-5.15Upgrade linux-raspiUpgrade linux-gkeopUpgrade linux-intel-iotgUpgrade linux-lowlatency | Nov 19, 2024 | Oct 21, 2024 |
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