UBUNTU-CVE-2026-72135: High severity ubuntu/linux-hwe-edge vulnerability
In 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 FMODEPREAD and FMODEPWRITE enabled. After a command leaves a response pending, pread(fd, buf, 16, 0x1400) passes 0x1400 as off to tpmcommonread(). The transfer length is bounded by responselength, but the offset is used unchecked when forming databuffer + off. A sufficiently large offset therefore causes an out-of-bounds heap read through copytouser() 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 databuffer, while pwrite() does not update file->fpos and can leave the sequential read cursor stale. Call nonseekableopen() from both open handlers. This removes FMODEPREAD and FMODEPWRITE, 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 fpos 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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Configuration
Call nonseekable_open() from both TPM character-device open handlers so positional reads and writes fail with -ESPIPE and the files are explicitly marked non-seekable.
Linux kernel TPM character devices FMODE_PREAD and FMODE_PWRITE = disabled
Event History
Frequently Asked Questions
Who can exploit this issue?
Exploitation requires local access and high privileges. An attacker must be able to open a TPM character device and issue positional I/O operations against it.
What operations trigger the vulnerable behavior?
A positional read using pread() with a sufficiently large offset after a TPM command has left a response pending can cause an out-of-bounds heap read and subsequent zero-write. Positional writes using pwrite() also have incoherent cursor behavior on this interface.
How can I tell whether a system is exposed?
Systems using the listed Ubuntu Linux kernel packages are in scope. The affected interface is the TPM character-device command/response interface, specifically where positional reads or writes are accepted rather than rejected with -ESPIPE.
What does the fix change?
The fix makes TPM character devices non-seekable by calling nonseekable_open() in both open handlers. This disables positional reads and writes so pread() and pwrite() fail with -ESPIPE before reaching TPM callbacks.