Re: [GIT PULL] SELinux fixes for v5.16 (#3)

On Fri, Dec 17, 2021 at 12:02 PM Paul Moore [off-list ref] wrote:

Another small SELinux fix for v5.16 to ensure that we don't block on
memory allocations while holding a spinlock.  This passes all our
tests without problem, please merge this for the next v5.16-rcX
release.

Ugh, pulled.

GFP_NOWAIT can very easily fail, so I'm not convinced your tests would
catch any of the interesting cases.

There is only one single caller of the new
security_sb_mnt_opts_compat() callback, and I get the feeling that
maybe we could parse the options first - into a temporary new
superblock, and then at "test" time (when we're under that sb_lock) it
could compare that temporary sb with pre-existing ones?

That would also avoid the need for doing that mount option parsing
over and over and over again for each sb on the 'fs_supers' lists.

I've pulled this, bit it does smell bad to me, and I think that
original commit 69c4a42d72eb ("lsm,selinux: add new hook to compare
new mount to an existing mount") and ec1ade6a0448 ("nfs: account for
selinux security context when deciding to share superblock") may not
have been fully thought out.

It may have *looked* like just adding that check  to
'nfs_compare_super' was a simple and good idea, but it really doesn't
look great.

Adding a few more people to the cc.

                 Linus