Amazon Linux AMI: CVE-2022-49287: Security patch for kernel (ALAS-2022-1591)

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

tpm: fix reference counting for struct tpm_chip

The following sequence of operations results in a refcount warning:

1. Open device /dev/tpmrm.

2. Remove module tpm_tis_spi.

3. Write a TPM command to the file descriptor opened at step 1.

------------[ cut here ]------------

WARNING: CPU: 3 PID: 1161 at lib/refcount.c:25 kobject_get+0xa0/0xa4

refcount_t: addition on 0; use-after-free.

Modules linked in: tpm_tis_spi tpm_tis_core tpm mdio_bcm_unimac brcmfmac

sha256_generic libsha256 sha256_arm hci_uart btbcm bluetooth cfg80211 vc4

brcmutil ecdh_generic ecc snd_soc_core crc32_arm_ce libaes

raspberrypi_hwmon ac97_bus snd_pcm_dmaengine bcm2711_thermal snd_pcm

snd_timer genet snd phy_generic soundcore [last unloaded: spi_bcm2835]

CPU: 3 PID: 1161 Comm: hold_open Not tainted 5.10.0ls-main-dirty #2

Hardware name: BCM2711

[<c0410c3c>] (unwind_backtrace) from [<c040b580>] (show_stack+0x10/0x14)

[<c040b580>] (show_stack) from [<c1092174>] (dump_stack+0xc4/0xd8)

[<c1092174>] (dump_stack) from [<c0445a30>] (__warn+0x104/0x108)

[<c0445a30>] (__warn) from [<c0445aa8>] (warn_slowpath_fmt+0x74/0xb8)

[<c0445aa8>] (warn_slowpath_fmt) from [<c08435d0>] (kobject_get+0xa0/0xa4)

[<c08435d0>] (kobject_get) from [<bf0a715c>] (tpm_try_get_ops+0x14/0x54 [tpm])

[<bf0a715c>] (tpm_try_get_ops [tpm]) from [<bf0a7d6c>] (tpm_common_write+0x38/0x60 [tpm])

[<bf0a7d6c>] (tpm_common_write [tpm]) from [<c05a7ac0>] (vfs_write+0xc4/0x3c0)

[<c05a7ac0>] (vfs_write) from [<c05a7ee4>] (ksys_write+0x58/0xcc)

[<c05a7ee4>] (ksys_write) from [<c04001a0>] (ret_fast_syscall+0x0/0x4c)

Exception stack(0xc226bfa8 to 0xc226bff0)

bfa0: 00000000 000105b4 00000003 beafe664 00000014 00000000

bfc0: 00000000 000105b4 000103f8 00000004 00000000 00000000 b6f9c000 beafe684

bfe0: 0000006c beafe648 0001056c b6eb6944

---[ end trace d4b8409def9b8b1f ]---

The reason for this warning is the attempt to get the chip->dev reference

in tpm_common_write() although the reference counter is already zero.

Since commit 8979b02aaf1d ("tpm: Fix reference count to main device") the

extra reference used to prevent a premature zero counter is never taken,

because the required TPM_CHIP_FLAG_TPM2 flag is never set.

Fix this by moving the TPM 2 character device handling from

tpm_chip_alloc() to tpm_add_char_device() which is called at a later point

in time when the flag has been set in case of TPM2.

Commit fdc915f7f719 ("tpm: expose spaces via a device link /dev/tpmrm<n>")

already introduced function tpm_devs_release() to release the extra

reference but did not implement the required put on chip->devs that results

in the call of this function.

Fix this by putting chip->devs in tpm_chip_unregister().

Finally move the new implementation for the TPM 2 handling into a new

function to avoid multiple checks for the TPM_CHIP_FLAG_TPM2 flag in the

good case and error cases.