[Bug libc/29118] New: 64 bit time and seccomp conflict

[Bug libc/29118] New: 64 bit time and seccomp conflict

[alacki93 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29118

            Bug ID: 29118
           Summary: 64 bit time and seccomp conflict
           Product: glibc
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: alacki93 at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

I found that glibc with support for 64-bit time could crash process that uses
seccomp. Problem was figured in OpenSSH process. Test environment:
-Kernel 4.14.x
-32 bit ARM CPU
-glibc 2.34
-OpenSSH 8.9p1
-Toolchain: GCC 10

Syscall wrappers like a clock_gettime (sysdeps/unix/sysv/linux/clock_gettime.c)
first run syscall dedicated for kernels that support 64 bit time. If this
syscall failed with ENOSYS error, then glibc calls traditional variant for 32
bit time.

OpenSSH in source code tries to figure which syscalls are supported by kernel
and only supported syscalls are added as an allowed in seccomp
(https://github.com/openssh/openssh-portable/blob/master/sandbox-seccomp-filter.c).
Because kernel 4.14 doesn’t support syscalls for 64 bit time,
__NR_clock_gettime64 is not added as a trusted syscall to seccomp. As a result
OpenSSH process is killed by seccomp every time when it tries to use
clock_gettime from glibc.

I found that this problem affects OpenSSH, but probably there can be other
projects that uses seccomp in similar way. Proposed solution is to add a build
flag that could disable all syscalls with 64 bit time during glibc compilation.

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[Bug libc/29118] 64 bit time and seccomp conflict

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29118

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
This really isn't a glibc problem. It looks like you'll have to build OpenSSH
with newer kernel headers, or contribute system call number constants for
32-bit Arm to the portable OpenSSH project.

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