FKIE_CVE-2025-39723

Vulnerability from fkie_nvd - Published: 2025-09-05 18:15 - Updated: 2025-11-25 21:01
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: netfs: Fix unbuffered write error handling If all the subrequests in an unbuffered write stream fail, the subrequest collector doesn't update the stream->transferred value and it retains its initial LONG_MAX value. Unfortunately, if all active streams fail, then we take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set in wreq->transferred - which is then returned from ->write_iter(). LONG_MAX was chosen as the initial value so that all the streams can be quickly assessed by taking the smallest value of all stream->transferred - but this only works if we've set any of them. Fix this by adding a flag to indicate whether the value in stream->transferred is valid and checking that when we integrate the values. stream->transferred can then be initialised to zero. This was found by running the generic/750 xfstest against cifs with cache=none. It splices data to the target file. Once (if) it has used up all the available scratch space, the writes start failing with ENOSPC. This causes ->write_iter() to fail. However, it was returning wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought the amount transferred was non-zero) and iter_file_splice_write() would then try to clean up that amount of pipe bufferage - leading to an oops when it overran. The kernel log showed: CIFS: VFS: Send error in write = -28 followed by: BUG: kernel NULL pointer dereference, address: 0000000000000008 with: RIP: 0010:iter_file_splice_write+0x3a4/0x520 do_splice+0x197/0x4e0 or: RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282) iter_file_splice_write (fs/splice.c:755) Also put a warning check into splice to announce if ->write_iter() returned that it had written more than it was asked to.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/387164a2b97e1f5404c6d0049a7409bac7d2bc5bPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a3de58b12ce074ec05b8741fa28d62ccb1070468Patch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f08c80af3c9a9849cd178b4843b7c01d103506a1Patch
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel *
linux linux_kernel 6.17
linux linux_kernel 6.17
To clipboard 

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  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfs: Fix unbuffered write error handling\n\nIf all the subrequests in an unbuffered write stream fail, the subrequest\ncollector doesn\u0027t update the stream-\u003etransferred value and it retains its\ninitial LONG_MAX value.  Unfortunately, if all active streams fail, then we\ntake the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set\nin wreq-\u003etransferred - which is then returned from -\u003ewrite_iter().\n\nLONG_MAX was chosen as the initial value so that all the streams can be\nquickly assessed by taking the smallest value of all stream-\u003etransferred -\nbut this only works if we\u0027ve set any of them.\n\nFix this by adding a flag to indicate whether the value in\nstream-\u003etransferred is valid and checking that when we integrate the\nvalues.  stream-\u003etransferred can then be initialised to zero.\n\nThis was found by running the generic/750 xfstest against cifs with\ncache=none.  It splices data to the target file.  Once (if) it has used up\nall the available scratch space, the writes start failing with ENOSPC.\nThis causes -\u003ewrite_iter() to fail.  However, it was returning\nwreq-\u003etransferred, i.e. LONG_MAX, rather than an error (because it thought\nthe amount transferred was non-zero) and iter_file_splice_write() would\nthen try to clean up that amount of pipe bufferage - leading to an oops\nwhen it overran.  The kernel log showed:\n\n    CIFS: VFS: Send error in write = -28\n\nfollowed by:\n\n    BUG: kernel NULL pointer dereference, address: 0000000000000008\n\nwith:\n\n    RIP: 0010:iter_file_splice_write+0x3a4/0x520\n    do_splice+0x197/0x4e0\n\nor:\n\n    RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282)\n    iter_file_splice_write (fs/splice.c:755)\n\nAlso put a warning check into splice to announce if -\u003ewrite_iter() returned\nthat it had written more than it was asked to."
    }
  ],
  "id": "CVE-2025-39723",
  "lastModified": "2025-11-25T21:01:02.797",
  "metrics": {
    "cvssMetricV31": [
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        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
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        "impactScore": 5.9,
        "source": "nvd@nist.gov",
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  "published": "2025-09-05T18:15:50.043",
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