[hurd] 07/98: proc: fix a use-after-free error

[Samuel Thibault]

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sthibault pushed a commit to branch upstream
in repository hurd.

commit 20fdd28047bfe8fabb7cebbda49386f4cab3c020
Author: Justus Winter <address@hidden>
Date:   Wed Nov 6 14:55:47 2013 +0100

    proc: fix a use-after-free error
    
    If we have to create a new process group, we have to do this before
    leaving the current one. The current process group is deallocated if
    the process is the last process in that group. Likewise, if the
    current group was the last group in the current groups session, the
    session is deallocated.
    
    Found using the Clang Static Analyzer.
    
    * proc/pgrp.c (S_proc_setpgrp): Fix use-after-free error.
---
 proc/pgrp.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/proc/pgrp.c b/proc/pgrp.c
index d4ea9ee..a828e17 100644
--- a/proc/pgrp.c
+++ b/proc/pgrp.c
@@ -341,8 +341,14 @@ S_proc_setpgrp (struct proc *callerp,
 
   if (p->p_pgrp != pg)
     {
+      /* If we have to create a new pgrp, we have to do this before
+        leaving the current one.  p->p_pgrp is deallocated if p is
+        the last process in that group.  Likewise, if p->p_pgrp was
+        the last group in p->p_pgrp->pg_session, the session is
+        deallocated.  */
+      struct pgrp *new = pg ? pg : new_pgrp (pgid, p->p_pgrp->pg_session);
       leave_pgrp (p);
-      p->p_pgrp = pg ? pg : new_pgrp (pgid, p->p_pgrp->pg_session);
+      p->p_pgrp = new;
       join_pgrp (p);
     }
   else

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