[Bug libc/28377] closefrom_fallback fails when /proc/self/fd is not present, which causes unexpected behavior with openssh

["adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28377

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

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                 CC|                            |adhemerval.zanella at linaro dot o
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--- Comment #2 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
As Florian has state in the https://bugzilla.mindrot.org/show_bug.cgi?id=3349,
there is not much we can do make it work reliable on Linux. The RLIMIT_NOFILE
fallback some implementations (such the one used on openssh at
openbsd-compat/bsd-closefrom.c) is not possible because it does not really
describe the descriptor range, and iterating over all possible file descriptors
values (INT_MAX) is prohibitively performance-wise. It might work on openssh
since it controls when and how it uses RLIMIT_NOFILE, but it not an option for
glibc.

So I think it is a fair assumption that if you want to support closefrom() on a
kernel without the syscall suppport, you need to provide the another feasible
kernel interface to allows it (procfs).

Another option is to either abort if /proc can not be opened or remove the
fallback (and abort() as well).

In any case, I am inclined to close this bug.

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