Re: [PATCH 2/2] tpm: Fix crash on tmprm release
From: Jarkko Sakkinen <jarkko@kernel.org>
Date: 2021-06-15 13:18:52
Also in:
lkml
On Tue, Jun 15, 2021 at 11:14:09AM +0200, Vincent Whitchurch wrote:
If the tpm_tis module is removed (or a system shutdown is triggered) while the tpmrm device is use, the kernel crashes due to chip->ops being NULL: # exec 3<>/dev/tpmrm0 # rmmod tpm_tis # exit ================================================================== BUG: KASAN: null-ptr-deref in tpm_chip_start+0x2d/0x120 [tpm] Read of size 8 at addr 0000000000000060 by task sh/994 Call Trace: kasan_report.cold.13+0x10f/0x111 tpm_chip_start+0x2d/0x120 [tpm] tpm2_del_space+0x2c/0xa0 [tpm] tpmrm_release+0x3f/0x50 [tpm] __fput+0x110/0x3c0 task_work_run+0x94/0xd0 do_exit+0x683/0x13e0 do_group_exit+0x8b/0x140 do_syscall_64+0x3c/0x80 ================================================================== Fix this by making tpm2_del_space() use tpm_try_get_ops(). The latter already includes the calls to tpm_chip_start() and tpm_chip_stop().
This lacks explanation why migrating to tpm_try_get_ops() fixes the issue. Saying that doing something fixes something is not good enough explanation. So, can you extend this paragraph just a bit in the next version?
quoted hunk ↗ jump to hunk
Signed-off-by: Vincent Whitchurch <redacted> --- drivers/char/tpm/tpm2-space.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c index 784b8b3cb903..e1111261021f 100644 --- a/drivers/char/tpm/tpm2-space.c +++ b/drivers/char/tpm/tpm2-space.c@@ -58,12 +58,10 @@ int tpm2_init_space(struct tpm_space *space, unsigned int buf_size) void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space) { - mutex_lock(&chip->tpm_mutex); - if (!tpm_chip_start(chip)) { + if (!tpm_try_get_ops(chip)) { tpm2_flush_sessions(chip, space); - tpm_chip_stop(chip); + tpm_put_ops(chip); } - mutex_unlock(&chip->tpm_mutex); kfree(space->context_buf); kfree(space->session_buf); }-- 2.28.0
/Jarkko