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useradd: Correctly set subuid/subgid when using -F #1511

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useradd: Correctly set subuid/subgid when using -F #1511

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6 changes: 2 additions & 4 deletions src/useradd.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2511,12 +2511,10 @@ int main (int argc, char **argv)
subgid_count = getdef_ulong ("SUB_GID_COUNT", 65536);
is_sub_uid = want_subuid_file () &&
subuid_count > 0 && sub_uid_file_present () &&
(!rflg || Fflg) &&
(!user_id || (user_id <= uid_max && user_id >= uid_min));
(!rflg && (!user_id || (user_id <= uid_max && user_id >= uid_min))) || Fflg;
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@alejandro-colomar alejandro-colomar Jan 18, 2026

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This seems brittle. It is affected by the fact that && has more precedence than ||, which is something not well known.

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@acdn-ndostert acdn-ndostert Jan 18, 2026

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Sorry I'm more a Python person, I can mostly read C code but not really write it.
Doesn't the parenthesis group the tests so there is not && and || in the same test ?

(
  !rflg && (
    !user_id || (
      user_id <= uid_max &&  user_id >= uid_min
    )
  )
) || Fflg;

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@alejandro-colomar alejandro-colomar Jan 18, 2026 •
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Yes, but you have the full expression (see lines 2513 and above) as

a && b && && c && (...) || e

Those && and || don't necessarily interact as you'd expect.

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@acdn-ndostert acdn-ndostert Jan 20, 2026

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Yes, but you have the full expression (see lines 2513 and above) as

a && b && && c && (...) || e

Those && and || don't necessarily interact as you'd expect.

Ah yes I see, well I'm out of my depth on that.
I will see if I can either "prove" this work or fix it.

And also, thanks for your help !

is_sub_gid = want_subgid_file() &&
subgid_count > 0 && sub_gid_file_present() &&
(!rflg || Fflg) &&
(!user_id || (user_id <= uid_max && user_id >= uid_min));
(!rflg && (!user_id || (user_id <= uid_max && user_id >= uid_min))) || Fflg;
#endif /* ENABLE_SUBIDS */

if (run_parts ("/etc/shadow-maint/useradd-pre.d", user_name,
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