New: execve may return EAGAIN on v3.1 or later

https://bugzilla.kernel.org/show_bug.cgi?id=42704

Summary: execve may return EAGAIN on v3.1 or later
Product: Documentation
Version: unspecified
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
AssignedTo: documentation_man-pages-ztI5WcYan/[email protected]
ReportedBy: [email protected]
Regression: No

Following commit changed RLIMIT_NPROC rule. now set*uid() never return EAGAIN. And instead,
execve() may return EAGAIN.

If man pages respect this change, it would be better.

commit 72fa59970f8698023045ab0713d66f3f4f96945c

Author: Vasiliy Kulikov 
Date:   Mon Aug 8 19:02:04 2011 +0400

move RLIMIT_NPROC check from set_user() to do_execve_common()

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https://bugzilla.kernel.org/show_bug.cgi?id=42704

Michael Kerrisk <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #1 from Michael Kerrisk <[email protected]> 2012-04-17 19:03:47 --- Vasiliy,

Thanks for raising this bug. I think the best approach would be to leave the existing EAGAIN text in the set*uid pages (possibly with a note about v3.1 changes), and add some text to the execve.2 page.

However, I have a question: I can understand adding the check to execve(), but why was it removed from set*uid()? Surely it was still useful to applications that actually do check the return status from set*uid()?

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https://bugzilla.kernel.org/show_bug.cgi?id=42704

--- Comment #2 from KOSAKI Motohiro <[email protected]> 2012-04-18 00:23:10 --- Hmm..

I'm not Vasiliy and I couldn't add him to cc list (I don't know why). But maybe I can answer this.

Now, many many applications don't check the return code and this ignorance may make critical security issue. set*id() is usually used for dropping root privilege
and then a failure mean application run untrusted code w/ root privilege.
that's dangerous. then, set*id() should ignore rlimit and always can drop a privilege.

In the other hand, execve() is used for getting a privilege. then a failure is not security threat.

Next, applications still should check set*uid() return value because it may run on older kernel.

thank you.

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https://bugzilla.kernel.org/show_bug.cgi?id=42704

Michael Kerrisk <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------

             Status|NEW                         |RESOLVED
         Resolution|---                         |CODE_FIX

--- Comment #3 from Michael Kerrisk <[email protected]> --- Patch (ebd381ba7b73) sitting in Git. Will be released with man-pages-3.69.

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