GHSA-MGW8-PG67-5PW5
Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-17 06:33In the Linux kernel, the following vulnerability has been resolved:
tpm: Make the TPM character devices non-seekable
The TPM character devices expose a sequential command/response interface, but their open handlers leave FMODE_PREAD and FMODE_PWRITE enabled.
After a command leaves a response pending, pread(fd, buf, 16, 0x1400) passes 0x1400 as off to tpm_common_read(). The transfer length is bounded by response_length, but the offset is used unchecked when forming data_buffer + off. A sufficiently large offset therefore causes an out-of-bounds heap read through copy_to_user() and, if the copy succeeds, an out-of-bounds zero-write through the following memset().
Positional I/O does not provide coherent semantics for this interface. An arbitrary pread offset cannot represent how much of a response has been consumed sequentially. The write callback always stores a command at the start of data_buffer, while pwrite() does not update file->f_pos and can leave the sequential read cursor stale.
Call nonseekable_open() from both open handlers. This removes FMODE_PREAD and FMODE_PWRITE, causing positional reads and writes to fail with -ESPIPE before reaching the TPM callbacks, and explicitly marks the files non-seekable. Normal read() and write() continue to use the existing sequential f_pos cursor, leaving the response state machine unchanged.
Tested on Linux 6.12 with KASAN and a swtpm TPM2 device:
- sequential partial reads returned the complete response
- pread() and preadv() with offset 0x1400 returned -ESPIPE
- pwrite() and pwritev() with offset zero returned -ESPIPE
- the pending response remained intact after the rejected operations
- a subsequent normal command/response cycle completed normally
- no KASAN report was produced.
{
"affected": [],
"aliases": [
"CVE-2026-72135"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-15T06:21:30Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntpm: Make the TPM character devices non-seekable\n\nThe TPM character devices expose a sequential command/response\ninterface, but their open handlers leave FMODE_PREAD and FMODE_PWRITE\nenabled.\n\nAfter a command leaves a response pending, pread(fd, buf, 16, 0x1400)\npasses 0x1400 as *off to tpm_common_read(). The transfer length is\nbounded by response_length, but the offset is used unchecked when\nforming data_buffer + *off. A sufficiently large offset therefore causes\nan out-of-bounds heap read through copy_to_user() and, if the copy\nsucceeds, an out-of-bounds zero-write through the following memset().\n\nPositional I/O does not provide coherent semantics for this interface.\nAn arbitrary pread offset cannot represent how much of a response has\nbeen consumed sequentially. The write callback always stores a command\nat the start of data_buffer, while pwrite() does not update file-\u003ef_pos\nand can leave the sequential read cursor stale.\n\nCall nonseekable_open() from both open handlers. This removes\nFMODE_PREAD and FMODE_PWRITE, causing positional reads and writes to\nfail with -ESPIPE before reaching the TPM callbacks, and explicitly\nmarks the files non-seekable. Normal read() and write() continue to use\nthe existing sequential f_pos cursor, leaving the response state machine\nunchanged.\n\nTested on Linux 6.12 with KASAN and a swtpm TPM2 device:\n\n - sequential partial reads returned the complete response\n - pread() and preadv() with offset 0x1400 returned -ESPIPE\n - pwrite() and pwritev() with offset zero returned -ESPIPE\n - the pending response remained intact after the rejected operations\n - a subsequent normal command/response cycle completed normally\n - no KASAN report was produced.",
"id": "GHSA-mgw8-pg67-5pw5",
"modified": "2026-08-17T06:33:12Z",
"published": "2026-08-15T06:32:13Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-72135"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/21a13f932972bc9836f58c44fcd47c62abdecd95"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/232dcf908eb7eb9d8046a9597975caf44270966e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/947b773caaa548672184df025271b29bdc80b0f1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9c513dabd4540f811585a2087f23069767a284da"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ada4b9a5087ea7f30dd8e4c6411a4fb6547eb1ed"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dda695fab5e21f923d29e8cb01df256468ddfbd1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ed0ffc2c016629e40ba041ed0424a772d8b02e2c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f20d61c22bcaf172d6790b6500e3838e532e71c8"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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