CVE-2025-39684 (GCVE-0-2025-39684)
Vulnerability from cvelistv5
Published
2025-09-05 17:20
Modified
2025-09-29 05:57
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
comedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()
syzbot reports a KMSAN kernel-infoleak in `do_insn_ioctl()`. A kernel
buffer is allocated to hold `insn->n` samples (each of which is an
`unsigned int`). For some instruction types, `insn->n` samples are
copied back to user-space, unless an error code is being returned. The
problem is that not all the instruction handlers that need to return
data to userspace fill in the whole `insn->n` samples, so that there is
an information leak. There is a similar syzbot report for
`do_insnlist_ioctl()`, although it does not have a reproducer for it at
the time of writing.
One culprit is `insn_rw_emulate_bits()` which is used as the handler for
`INSN_READ` or `INSN_WRITE` instructions for subdevices that do not have
a specific handler for that instruction, but do have an `INSN_BITS`
handler. For `INSN_READ` it only fills in at most 1 sample, so if
`insn->n` is greater than 1, the remaining `insn->n - 1` samples copied
to userspace will be uninitialized kernel data.
Another culprit is `vm80xx_ai_insn_read()` in the "vm80xx" driver. It
never returns an error, even if it fails to fill the buffer.
Fix it in `do_insn_ioctl()` and `do_insnlist_ioctl()` by making sure
that uninitialized parts of the allocated buffer are zeroed before
handling each instruction.
Thanks to Arnaud Lecomte for their fix to `do_insn_ioctl()`. That fix
replaced the call to `kmalloc_array()` with `kcalloc()`, but it is not
always necessary to clear the whole buffer.
References
Impacted products
| Vendor | Product | Version | |||||||
|---|---|---|---|---|---|---|---|---|---|
| ▼ | Linux | Linux |
Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Version: ed9eccbe8970f6eedc1b978c157caf1251a896d4 |
||||||
|
|||||||||
{
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ncomedi: Fix use of uninitialized memory in do_insn_ioctl() and do_insnlist_ioctl()\n\nsyzbot reports a KMSAN kernel-infoleak in `do_insn_ioctl()`. A kernel\nbuffer is allocated to hold `insn-\u003en` samples (each of which is an\n`unsigned int`). For some instruction types, `insn-\u003en` samples are\ncopied back to user-space, unless an error code is being returned. The\nproblem is that not all the instruction handlers that need to return\ndata to userspace fill in the whole `insn-\u003en` samples, so that there is\nan information leak. There is a similar syzbot report for\n`do_insnlist_ioctl()`, although it does not have a reproducer for it at\nthe time of writing.\n\nOne culprit is `insn_rw_emulate_bits()` which is used as the handler for\n`INSN_READ` or `INSN_WRITE` instructions for subdevices that do not have\na specific handler for that instruction, but do have an `INSN_BITS`\nhandler. For `INSN_READ` it only fills in at most 1 sample, so if\n`insn-\u003en` is greater than 1, the remaining `insn-\u003en - 1` samples copied\nto userspace will be uninitialized kernel data.\n\nAnother culprit is `vm80xx_ai_insn_read()` in the \"vm80xx\" driver. It\nnever returns an error, even if it fails to fill the buffer.\n\nFix it in `do_insn_ioctl()` and `do_insnlist_ioctl()` by making sure\nthat uninitialized parts of the allocated buffer are zeroed before\nhandling each instruction.\n\nThanks to Arnaud Lecomte for their fix to `do_insn_ioctl()`. That fix\nreplaced the call to `kmalloc_array()` with `kcalloc()`, but it is not\nalways necessary to clear the whole buffer."
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"url": "https://git.kernel.org/stable/c/3cd212e895ca2d58963fdc6422502b10dd3966bb"
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"datePublished": "2025-09-05T17:20:50.827Z",
"dateReserved": "2025-04-16T07:20:57.113Z",
"dateUpdated": "2025-09-29T05:57:21.980Z",
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