[Bug network/31476] New: Automatic activation of single-request options break resolv.conf reloading

[Bug network/31476] New: Automatic activation of single-request options break resolv.conf reloading

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31476

            Bug ID: 31476
           Summary: Automatic activation of single-request options break
                    resolv.conf reloading
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: network
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---
             Flags: security-

Initial report from John Levon:

Issue with stale resolv.conf state
<https://inbox.sourceware.org/libc-alpha/Ze7KCkIzR5PuErba@movementarian.org/>

John traced the lack of reloading to a change in _res.options:

“
I don't understand the first part of the comment, but indeed, ->resp doesn't
match. In particular:

 62   return ctx->resp->options == ctx->conf->options                           

and ctx->resp (aka _resp) has 0x47002c1 whereas ctx->conf has 0x41002c1.

I'm not sure but I suspect the additional RES_SNGLKUP|RES_SNGLKUPREOP may be
due
to this code:

1000                     /* There are quite a few broken name servers out       
1001                        there which don't handle two outstanding            
1002                        requests from the same source.  There are also      
1003                        broken firewall settings.  If we time out after     
1004                        having received one answer switch to the mode       
1005                        where we send the second request only once we       
1006                        have received the first answer.  */                 
1007                     if (!single_request)                                   
1008                       {                                                    
1009                         statp->options |= RES_SNGLKUP;                     
1010                         single_request = true;                             
1011                         *gotsomewhere = save_gotsomewhere;                 
1012                         goto retry;                                        
1013                       }                                                    
1014                     else if (!single_request_reopen)                       
1015                       {                                                    
1016                         statp->options |= RES_SNGLKUPREOP;                 
1017                         single_request_reopen = true;                      
1018                         *gotsomewhere = save_gotsomewhere;                 
1019                         __res_iclose (statp, false);                       
1020                         goto retry_reopen;                                 
1021                       }                                                    

I'm guessing these got set when the VPN dropped routing to the old nameservers,
but before the next getaddrinfo() came in, thus leading to the match failing.
”

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[Bug network/31476] Automatic activation of single-request options break resolv.conf reloading

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=31476

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=29017

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[Bug network/31476] Automatic activation of single-request options break resolv.conf reloading

[levon at movementarian dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31476

John Levon <levon at movementarian dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |levon at movementarian dot org

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