[PATCH] getXXent_r and getXXbyYY_r not really thread safe

[Thorsten Kukuk]

On Mon, Sep 13, Ulrich Drepper wrote:

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> That is by design.  Different threads can use the getXXent functions
> together.  Since these functions are not to be used anyway there is not
> need to make this more complicated.
> 
> And now it is completely out of question to change this anyway, it
> breaks the ABI which exists for more than 8 years now.  There might as
> well be code depending on this behavior.

But this behavior is contrary to the behavior of commercial Unix
systems. 

And there are two other problems: 

1. We use the getXXent functions internal from getXXbyYY_r functions
   in all NSS modules, even the nss_files module does so. This means,
   if two threads calls a getXXbyYY_r function, it can happen that one
   function returns wrong a "not found" error. I got more than one
   report for the servent functions, which make heavyly use of this.
   The netgroup functions have a similar problem, as result, if you
   use netgroups in /etc/passwd, an account is suddenly no longer allowed
   to login or, for /etc/exports, a client is suddenly no longer allowed
   to mount a share.

2. Calling getXXbyYY_r() from concurrent threads could mean, that
   the service pointer in libc could be changed at a time in such a
   way, that the second thread will never get the data from one
   service.


Both failures will happen more often as more programs will use
threads.

  Thorsten

-- 
Thorsten Kukuk       http://www.suse.de/~kukuk/        kukuk@suse.de
SuSE Linux AG        Maxfeldstr. 5                 D-90409 Nuernberg
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