[bug #62621] xargs/find: buildcmd incorrectly sizes argv and envp

[Thomas Hurst]

URL:
  <https://savannah.gnu.org/bugs/?62621>

                 Summary: xargs/find: buildcmd incorrectly sizes argv and envp
                 Project: findutils
               Submitter: freaky
               Submitted: Mon 13 Jun 2022 01:24:21 PM UTC
                Category: xargs
                Severity: 3 - Normal
              Item Group: Wrong result
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: None
         Discussion Lock: Any
           Fixed Release: None


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Follow-up Comments:


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Date: Mon 13 Jun 2022 01:24:21 PM UTC By: Thomas Hurst <freaky>
buildcmd.c calculates the size of both arguments and environment entries as
strlen(s) + 1 - the size of the string plus delimiter.

This fails to take into account the argv/envp pointer to each entry, which at
least on Linux also contributes to the limit. To quote bprm_stack_limits()
from fs/exec.c:

> We must account for the size of all the argv and envp pointers to
> the argv and envp strings, since they will also take up space in
> the stack.

And indeed, sizeof(void*)*argc+envc are subtracted from the limit it
enforces.

This issue is masked by xargs defaulting to quite modest limits, and retrying
automatically with smaller sizes on E2BIG - though in testing this I find what
appears to be another issue, which I will file separately.







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