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commit 31d0a4fa646db8b8c97ce24e0ec0a7b73de4fca1
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Author: Florian Weimer <fweimer@redhat.com>
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Date:   Sat Jun 11 12:12:56 2016 +0200
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    nss_db: Fix initialization of iteration position [BZ #20237]
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    When get*ent is called without a preceding set*ent, we need
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    to set the initial iteration position in get*ent.
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    Reproducer: Add “services: db files” to /etc/nsswitch.conf, then run
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    “perl -e getservent”.  It will segfault before this change, and exit
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    silently after it.
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Index: b/nss/nss_db/db-XXX.c
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===================================================================
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--- a/nss/nss_db/db-XXX.c
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+++ b/nss/nss_db/db-XXX.c
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@@ -76,7 +76,7 @@ CONCAT(_nss_db_set,ENTNAME) (int stayope
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       keep_db |= stayopen;
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       /* Reset the sequential index.  */
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-      entidx  = (const char *) state.header + state.header->valstroffset;
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+      entidx  = NULL;
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     }
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   __libc_lock_unlock (lock);
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@@ -249,8 +249,14 @@ CONCAT(_nss_db_get,ENTNAME_r) (struct ST
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 	  H_ERRNO_SET (NETDB_INTERNAL);
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 	  goto out;
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 	}
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+      entidx = NULL;
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     }
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+  /* Start from the beginning if freshly initialized or reset
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+     requested by set*ent.  */
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+  if (entidx == NULL)
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+    entidx = (const char *) state.header + state.header->valstroffset;
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+
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   status = NSS_STATUS_UNAVAIL;
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   if (state.header != MAP_FAILED)
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     {