CVE-2026-72135

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 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 Software

References

• https://git.kernel.org/stable/c/21a13f932972bc9836f58c44fcd47c62abdecd95
• https://git.kernel.org/stable/c/232dcf908eb7eb9d8046a9597975caf44270966e
• https://git.kernel.org/stable/c/947b773caaa548672184df025271b29bdc80b0f1
• https://git.kernel.org/stable/c/9c513dabd4540f811585a2087f23069767a284da
• https://git.kernel.org/stable/c/ada4b9a5087ea7f30dd8e4c6411a4fb6547eb1ed
• https://git.kernel.org/stable/c/dda695fab5e21f923d29e8cb01df256468ddfbd1
• https://git.kernel.org/stable/c/ed0ffc2c016629e40ba041ed0424a772d8b02e2c
• https://git.kernel.org/stable/c/f20d61c22bcaf172d6790b6500e3838e532e71c8