CVE-2025-39723 (GCVE-0-2025-39723)

Vulnerability from cvelistv5 – Published: 2025-09-05 17:21 – Updated: 2026-08-05 12:04
VLAI
Title
netfs: Fix unbuffered write error handling
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.
Severity
7.1 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 288ace2f57c9d06dd2e42bd80d03747d879a4068 , < f08c80af3c9a9849cd178b4843b7c01d103506a1 (git)
Affected: 288ace2f57c9d06dd2e42bd80d03747d879a4068 , < 387164a2b97e1f5404c6d0049a7409bac7d2bc5b (git)
Affected: 288ace2f57c9d06dd2e42bd80d03747d879a4068 , < a3de58b12ce074ec05b8741fa28d62ccb1070468 (git)
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Linux Linux Affected: 6.10
Unaffected: 0 , < 6.10 (semver)
Unaffected: 6.12.44 , ≤ 6.12.* (semver)
Unaffected: 6.16.4 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
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        "id": "CVE-2025-39723",
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      "current_release_date": "2026-07-30T08:58:25+00:00",
      "cve": "CVE-2025-39723",
      "id": "CVE-2025-39723",
      "initial_release_date": "2025-09-05T00:00:00+00:00",
      "product_status:known_affected": "76",
      "product_status:known_not_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: netfs: Fix unbuffered write error handling",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39723.json",
      "version": "3"
    }
  }
}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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