(#2037807) Allow unprivileged users to send ICMP echo requests

[jamacku]

Upstream PR systemd/systemd#13191

Follow-up to #246

Resolves: #2037807

[mrc0mmand]

CI seems to be happy, I gave systemd-sysctl a brief check with ASan+UBsan (since the original backport caused a memory corruption) and that's sorted out as well. Also, ping is now available to unprivileged users again.

Old version:

# sysctl -w net.ipv4.ping_group_range="1 0"
net.ipv4.ping_group_range = 1 0
# sudo -u test ping localhost
ping: socket: Operation not permitted
# /usr/lib/systemd/systemd-sysctl 
Couldn't write '0 2147483647' to '-net/ipv4/ping_group_range', ignoring: No such file or directory
# sysctl net.ipv4.ping_group_range
net.ipv4.ping_group_range = 1	0
# sudo -u test ping localhost
ping: socket: Operation not permitted

New version:

# sysctl -w net.ipv4.ping_group_range="1 0"
net.ipv4.ping_group_range = 1 0
# sudo -u test ping localhost
ping: socket: Operation not permitted
# /usr/lib/systemd/systemd-sysctl
# sysctl net.ipv4.ping_group_range
net.ipv4.ping_group_range = 0	2147483647
# sudo -u test ping localhost
PING localhost(localhost (::1)) 56 data bytes
64 bytes from localhost (::1): icmp_seq=1 ttl=64 time=0.046 ms
...

[mrc0mmand]

And just for completeness, the "ignore" mechanic seems to work as well:

# echo "fs.protected_symlinks = 9999" >>/usr/lib/sysctl.d/50-default.conf
# /usr/lib/systemd/systemd-sysctl; echo $?
Couldn't write '9999' to 'fs/protected_symlinks': Invalid argument
1

# echo "-fs.protected_symlinks = 9999" >>/usr/lib/sysctl.d/50-default.conf
# /usr/lib/systemd/systemd-sysctl; echo $?
Couldn't write '9999' to 'fs/protected_symlinks', ignoring: Invalid argument
0

[msekletar]

LGTM but before I approve...

@jamacku @mrc0mmand please triple-check there were no further follow-up bugfixes for these reworks. Hashmaps are in critical path and we must be 100% sure it is correct.

[mrc0mmand]

LGTM but before I approve...

@jamacku @mrc0mmand please triple-check there were no further follow-up bugfixes for these reworks. Hashmaps are in critical path and we must be 100% sure it is correct.

I went through the git log of each modified file:

• path_compare_func() is not used anywhere and could be safely dropped (was done in 6906ac9), but that shouldn't matter
• there's a memory leak in the path cache rebuilding... path, which is unrelated to this PR, but should be fixed nonetheless in the future (https://github.com/systemd/systemd/pull/15954/commits)
• there's c380b84 (and follow-up ca32371) which look like a good-to-have commits, so I pulled them in as well
  • nevermind, that would require a couple of other commits to be pulled in as well, not worth it imo
• db99904 is definitely something we should have; backported

That should be, hopefully, it.

[mrc0mmand]

We should merge this soon, since more and more uses are hitting the issue - @msekletar PTAL.

[msekletar]

LGTM