tpm: use try_get_ops() in tpm-space.c

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: tpm: use try_get_ops() in tpm-space.c As part of the series conversion to remove nested TPM operations: https://lore.kernel.org/all/20190205224723.19671-1-jarkko.sakkinen@linux.intel.com/ exposure of the chip->tpm_mutex was removed from much of the upper level code. In this conversion, tpm2_del_space() was missed. This didn't matter much because it's usually called closely after a converted operation, so there's only a very tiny race window where the chip can be removed before the space flushing is done which causes a NULL deref on the mutex. However, there are reports of this window being hit in practice, so fix this by converting tpm2_del_space() to use tpm_try_get_ops(), which performs all the teardown checks before acquring the mutex.

References

• https://git.kernel.org/stable/c/5b1d2561a03e534064b51c50c774657833d3d2cf
• https://git.kernel.org/stable/c/95193d12f10a8a088843b25e0f5fe1d83ec6b079
• https://git.kernel.org/stable/c/476ddd23f818fb94cf86fb5617f3bb9a7c92113d
• https://git.kernel.org/stable/c/eda1662cce964c8a65bb86321f8d9cfa6e9ceaab
• https://git.kernel.org/stable/c/ba84f9a48366dcc3cdef978599433efe101dd5bd
• https://git.kernel.org/stable/c/fb5abce6b2bb5cb3d628aaa63fa821da8c4600f9