Wrong permissions for datadir and walletdir #15902

On my Linux Mint 19.1:

$ umask
0022

After the first run of bitcoin-qt -sysperm=false the 0700 permissions are expected for both the datadir (~/.bitcoin) and the walletdir (~/.bitcoin/wallets).

Actually, the directories are created with such access permissions:

$ stat ~/.bitcoin | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
$ stat ~/.bitcoin/wallets | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)

Refs:

• #4286
• #13371
• #13389

NOTE: reading through the initial PR #4286 makes me think it was controversial. Is it a better and simpler way to just get rid of -sysperm option? I believe a user who needs this option can easily run chown command.

I'd suggest these changes:

• Wallets and block files are created with different permissions
• Introduce -walletperms option to change the default (600) to whatever user wants.
• Create block files with 644, the user can restrict it with umask

It solves this problem: running electr (needs to access blocks to be efficient) Eclair (needs wallet) and bitcoind under a different user. Currently one needs to give up efficiency or security.

I'm willing to do PR if you don't see any important problem with my suggestion.

Also: comment by @laanwj.