UBUNTU-CVE-2025-38100
In the Linux kernel, the following vulnerability has been resolved: x86/iopl: Cure TIF_IO_BITMAP inconsistencies io_bitmap_exit() is invoked from exit_thread() when a task exists or when a fork fails. In the latter case the exit_thread() cleans up resources which were allocated during fork(). io_bitmap_exit() invokes task_update_io_bitmap(), which in turn ends up in tss_update_io_bitmap(). tss_update_io_bitmap() operates on the current task. If current has TIF_IO_BITMAP set, but no bitmap installed, tss_update_io_bitmap() crashes with a NULL pointer dereference. There are two issues, which lead to that problem: 1) io_bitmap_exit() should not invoke task_update_io_bitmap() when the task, which is cleaned up, is not the current task. That's a clear indicator for a cleanup after a failed fork(). 2) A task should not have TIF_IO_BITMAP set and neither a bitmap installed nor IOPL emulation level 3 activated. This happens when a kernel thread is created in the context of a user space thread, which has TIF_IO_BITMAP set as the thread flags are copied and the IO bitmap pointer is cleared. Other than in the failed fork() case this has no impact because kernel threads including IO workers never return to user space and therefore never invoke tss_update_io_bitmap(). Cure this by adding the missing cleanups and checks: 1) Prevent io_bitmap_exit() to invoke task_update_io_bitmap() if the to be cleaned up task is not the current task. 2) Clear TIF_IO_BITMAP in copy_thread() unconditionally. For user space forks it is set later, when the IO bitmap is inherited in io_bitmap_share(). For paranoia sake, add a warning into tss_update_io_bitmap() to catch the case, when that code is invoked with inconsistent state.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
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36 explicit affected versions
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14 explicit affected versions
4 explicit affected versions
63 explicit affected versions
1 explicit affected versions
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50 explicit affected versions
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24 explicit affected versions
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5 explicit affected versions
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14 explicit affected versions
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37 explicit affected versions
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2 explicit affected versions
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29 explicit affected versions
13 explicit affected versions
6 explicit affected versions
78 explicit affected versions
32 explicit affected versions
32 explicit affected versions
73 explicit affected versions
36 explicit affected versions
33 explicit affected versions
23 explicit affected versions
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10 explicit affected versions
11 explicit affected versions
10 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
58 explicit affected versions
74 explicit affected versions
10 explicit affected versions
26 explicit affected versions
31 explicit affected versions
1 explicit affected versions
50 explicit affected versions
26 explicit affected versions
38 explicit affected versions
5 explicit affected versions
13 explicit affected versions
37 explicit affected versions
16 explicit affected versions
75 explicit affected versions
41 explicit affected versions
3 explicit affected versions
7 explicit affected versions
2 explicit affected versions
51 explicit affected versions
18 explicit affected versions
33 explicit affected versions
12 explicit affected versions
61 explicit affected versions
61 explicit affected versions
27 explicit affected versions
47 explicit affected versions
34 explicit affected versions
8 explicit affected versions
38 explicit affected versions
5 explicit affected versions
3 explicit affected versions
8 explicit affected versions
10 explicit affected versions
7 explicit affected versions
37 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
8 explicit affected versions
10 explicit affected versions
12 explicit affected versions
3 explicit affected versions
21 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
42 explicit affected versions
72 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
10 explicit affected versions
30 explicit affected versions
62 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: x86/iopl: Cure TIF_IO_BITMAP inconsistencies io_bitmap_exit() is invoked from exit_thread() when a task exists or when a fork fails. In the latter case the exit_thread() cleans up resources which were allocated during fork(). io_bitmap_exit() invokes task_update_io_bitmap(), which in turn ends up in tss_update_io_bitmap(). tss_update_io_bitmap() operates on the current task. If current has TIF_IO_BITMAP set, but no bitmap installed, tss_update_io_bitmap() crashes with a NULL pointer dereference. There are two issues, which lead to that problem: 1) io_bitmap_exit() should not invoke task_update_io_bitmap() when the task, which is cleaned up, is not the current task. That's a clear indicator for a cleanup after a failed fork(). 2) A task should not have TIF_IO_BITMAP set and neither a bitmap installed nor IOPL emulation level 3 activated. This happens when a kernel thread is created in the context of a user space thread, which has TIF_IO_BITMAP set as the thread flags are copied and the IO bitmap pointer is cleared. Other than in the failed fork() case this has no impact because kernel threads including IO workers never return to user space and therefore never invoke tss_update_io_bitmap(). Cure this by adding the missing cleanups and checks: 1) Prevent io_bitmap_exit() to invoke task_update_io_bitmap() if the to be cleaned up task is not the current task. 2) Clear TIF_IO_BITMAP in copy_thread() unconditionally. For user space forks it is set later, when the IO bitmap is inherited in io_bitmap_share(). For paranoia sake, add a warning into tss_update_io_bitmap() to catch the case, when that code is invoked with inconsistent state.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/8b68e978718f14fdcb080c2a7791c52a0d09bc6d
- https://git.kernel.org/stable/c/2cfcbe1554c119402e7382de974c26b0549899fe
- https://git.kernel.org/stable/c/2dace5e016c991424a3dc6e83b1ae5dca8992d08
- https://git.kernel.org/stable/c/73cfcc8445585b8af7e18be3c9246b851fdf336c
- https://git.kernel.org/stable/c/8b68e978718f14fdcb080c2a7791c52a0d09bc6d
- https://git.kernel.org/stable/c/aa5ce1485562f20235b4c759eee5ab0c41d2c220
- https://git.kernel.org/stable/c/b3b3b6366dc8eb5b22edba9adc4bff3cdacfd64c
- https://git.kernel.org/stable/c/d64b7b05a827f98d068f412969eef65489b0cf03
- https://ubuntu.com/security/CVE-2025-38100
- https://ubuntu.com/security/notices/USN-7769-1
- https://ubuntu.com/security/notices/USN-7769-2
- https://ubuntu.com/security/notices/USN-7769-3
- https://ubuntu.com/security/notices/USN-7770-1
- https://ubuntu.com/security/notices/USN-7771-1
- https://ubuntu.com/security/notices/USN-7774-1
- https://ubuntu.com/security/notices/USN-7774-2
- https://ubuntu.com/security/notices/USN-7774-3
- https://ubuntu.com/security/notices/USN-7774-4
- https://ubuntu.com/security/notices/USN-7774-5
- https://ubuntu.com/security/notices/USN-7775-1
- https://ubuntu.com/security/notices/USN-7775-2
- https://ubuntu.com/security/notices/USN-7775-3
- https://ubuntu.com/security/notices/USN-7776-1
- https://ubuntu.com/security/notices/USN-7789-1
- https://ubuntu.com/security/notices/USN-7789-2
- https://ubuntu.com/security/notices/USN-8028-1
- https://ubuntu.com/security/notices/USN-8028-2
- https://ubuntu.com/security/notices/USN-8028-3
- https://ubuntu.com/security/notices/USN-8028-4
- https://ubuntu.com/security/notices/USN-8028-5
- https://ubuntu.com/security/notices/USN-8028-6
- https://ubuntu.com/security/notices/USN-8028-7
- https://ubuntu.com/security/notices/USN-8028-8
- https://ubuntu.com/security/notices/USN-8031-1
- https://ubuntu.com/security/notices/USN-8031-2
- https://ubuntu.com/security/notices/USN-8031-3
- https://ubuntu.com/security/notices/USN-8052-1
- https://ubuntu.com/security/notices/USN-8052-2
- https://ubuntu.com/security/notices/USN-8074-1
- https://ubuntu.com/security/notices/USN-8074-2
- https://ubuntu.com/security/notices/USN-8126-1
- https://www.cve.org/CVERecord?id=CVE-2025-38100