In the Linux kernel, the following vulnerability has been resolved:

ima_fs: Correctly create securityfs files for unsupported hash algos

ima_tpm_chip->allocated_banks[i].crypto_id is initialized to HASH_ALGO__LAST if the TPM algorithm is not supported. However there are places relying on the algorithm to be valid because it is accessed by hash_algo_name[].

On 6.12.40 I observe the following read out-of-bounds in hash_algo_name:

BUG: KASAN: global-out-of-bounds in create_securityfs_measurement_lists+0x396/0x440 Read of size 8 at addr ffffffff83e18138 by task swapper/0/1

CPU: 4 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.12.40 #3 Call Trace: dump_stack_lvl+0x61/0x90 print_report+0xc4/0x580 ? kasan_addr_to_slab+0x26/0x80 ? create_securityfs_measurement_lists+0x396/0x440 kasan_report+0xc2/0x100 ? create_securityfs_measurement_lists+0x396/0x440 create_securityfs_measurement_lists+0x396/0x440 ima_fs_init+0xa3/0x300 ima_init+0x7d/0xd0 init_ima+0x28/0x100 do_one_initcall+0xa6/0x3e0 kernel_init_freeable+0x455/0x740 kernel_init+0x24/0x1d0 ret_from_fork+0x38/0x80 ret_from_fork_asm+0x11/0x20

The buggy address belongs to the variable: hash_algo_name+0xb8/0x420

Memory state around the buggy address: ffffffff83e18000: 00 01 f9 f9 f9 f9 f9 f9 00 01 f9 f9 f9 f9 f9 f9 ffffffff83e18080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

ffffffff83e18100: 00 00 00 00 00 00 00 f9 f9 f9 f9 f9 00 05 f9 f9 ^ ffffffff83e18180: f9 f9 f9 f9 00 00 00 00 00 00 00 04 f9 f9 f9 f9 ffffffff83e18200: 00 00 00 00 00 00 00 00 04 f9 f9 f9 f9 f9 f9 f9 ==================================================================

Seems like the TPM chip supports sha3_256, which isnt yet in tpm_algorithms: tpm tpm0: TPM with unsupported bank algorithm 0x0027

Thats TPM_ALG_SHA3_256 == 0x0027 from Trusted Platform Module 2.0 Library Part 2: Structures, page 51 1. See also the related U-Boot algorithms update 2.

Thus solve the problem by creating a file name with tpm_alg postfix if the crypto algorithm isnt initialized.

This is how it looks on the test machine (patch ported to v6.12 release):

ls -1 /sys/kernel/security/ima/

ascii_runtime_measurements ascii_runtime_measurements_tpm_alg_27 ascii_runtime_measurements_sha1 ascii_runtime_measurements_sha256 binary_runtime_measurements binary_runtime_measurements_tpm_alg_27 binary_runtime_measurements_sha1 binary_runtime_measurements_sha256 policy runtime_measurements_count violations

Affected Software

References

• https://git.kernel.org/stable/c/081b557cb56e1cfa8d1619b2601b01c53e3f418c
• https://git.kernel.org/stable/c/88d4e89a39f0de07798ca3fd93bd1a9ea212a82e
• https://git.kernel.org/stable/c/b6766b171a5c4c33b26ff6fec530cb798db1f75e
• https://git.kernel.org/stable/c/d7bd8cf0b348d3edae7bee33e74a32b21668b181