util: add linkat to syscall sandbox (AllowFileSystem) #24659

pull fanquake wants to merge 1 commits into bitcoin:master from fanquake:maybe_fix_24536 changing 1 files +1 −0

fanquake commented at 11:50 am on March 24, 2022: member

Should fix #24536.
util: add linkat to syscall sandbox (AllowFileSystem) 9809db3577
fanquake added the label Linux/Unix on Mar 24, 2022
fanquake added the label Utils/log/libs on Mar 24, 2022
MarcoFalke commented at 12:01 pm on March 24, 2022: member

cr ACK 9809db3577f0fa618bea42635b1581e628a30395

but might be good to test
luke-jr commented at 0:22 am on March 25, 2022: member

Should we allow regular link too? My manpage says glibc can fallback to link for emulating linkat on older kernels.
fanquake marked this as ready for review on Mar 25, 2022
fanquake commented at 7:44 am on March 25, 2022: member

Should we allow regular link too? My manpage says glibc can fallback to link for emulating linkat on older kernels.

Yes, if someone reports an issue with it. I don’t think we want/need to preemptively allow syscalls.
luke-jr commented at 1:18 pm on March 25, 2022: member

We don’t usually leave known bugs until someone reports them…
MarcoFalke commented at 1:25 pm on March 25, 2022: member

Yeah, I think it is fine to put in both.
fanquake commented at 1:34 pm on March 25, 2022: member

We don’t usually leave known bugs until someone reports them…

Sure, but this isn’t a known bug yet. If we want it to be one, can you elaborate more than “my manpage says maybe this is needed for some older kernels”.

Which manpage? Which older kernel (versions)? Which versions of glibc perform the fallback-ing? Do we support them? Can you reproduce the bug?

I’m not really interested in adding exceptions to our syscall sandbox based on hypotheticals derived from a possibly irrelevant (to our project & runtime back-compatibilities) sentence in a manpage. Especially if the problem hasn’t actually been run into in the wild.

in src/util/syscall_sandbox.cpp:595 in 9809db3577

591@@ -592,6 +592,7 @@ class SeccompPolicyBuilder
592         allowed_syscalls.insert(__NR_getcwd);          // get current working directory
593         allowed_syscalls.insert(__NR_getdents);        // get directory entries
594         allowed_syscalls.insert(__NR_getdents64);      // get directory entries
595+        allowed_syscalls.insert(__NR_linkat);          // create relative to a directory file descriptor

hebasto commented at 10:12 am on March 26, 2022:

Tested on Ubuntu 22.04:

0        allowed_syscalls.insert(__NR_inotify_rm_watch);// remove an existing watch from an inotify instance
1        allowed_syscalls.insert(__NR_linkat);          // create relative to a directory file descriptor

hebasto commented at 7:17 am on March 28, 2022:

Done in #24690.

Rspigler commented at 4:53 am on March 28, 2022: contributor

Tested ACK (commit 9809db3577f0fa618bea42635b1581e628a30395) - this fixes https://github.com/bitcoin/bitcoin/issues/24536
MarcoFalke commented at 7:04 am on March 28, 2022: member

Going to merge this, since it is tested and reviewed. Maybe issues on other OS can be fixed in a separate commit?
MarcoFalke merged this on Mar 28, 2022
MarcoFalke closed this on Mar 28, 2022
MarcoFalke added the label Needs backport (23.x) on Mar 28, 2022
fanquake deleted the branch on Mar 28, 2022
jonatack commented at 11:41 am on March 28, 2022: member

Backported to v23.0 in #24512
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Contributors
fanquake MarcoFalke luke-jr hebasto Rspigler jonatack

Labels
Linux/Unix Utils/log/libs