Initialize all of datahead structure in nscd (BZ #16791)

The datahead structure has an unused padding field that remains
uninitialized.  Valgrind prints out a warning for it on querying a
netgroups entry.  This is harmless, but is a potential data leak since
it would result in writing out an uninitialized byte to the cache
file.  Besides, this happens only when there is a cache miss, so we're
not adding computation to any fast path.

3 files changed, 23 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 942fb80..2b0821f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2014-04-30  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
+	[BZ #16791]
+	* nscd/nscd-client.h (datahead_init_common): Initialize entire
+	structure.
+	(datahead_init_pos): Call datahead_init_common early.
+	(datahead_init_neg): Likewise.
+
 	* nscd/nscd-client.h (datahead_init_common, datahead_init_pos,
 	datahead_init_neg): New functions.
 	* nscd/aicache.c (addhstaiX): Use them.
diff --git a/NEWS b/NEWS
index 10d2626..953f5ee 100644
--- a/NEWS
+++ b/NEWS
@@ -15,7 +15,7 @@ Version 2.20
   16632, 16634, 16639, 16642, 16648, 16649, 16670, 16674, 16677, 16680,
   16683, 16689, 16695, 16701, 16706, 16707, 16712, 16713, 16714, 16731,
   16739, 16740, 16743, 16754, 16758, 16759, 16760, 16770, 16786, 16789,
-  16799, 16800, 16815, 16823, 16824, 16831, 16838, 16854.
+  16791, 16799, 16800, 16815, 16823, 16824, 16831, 16838, 16854.
 
 * Running the testsuite no longer terminates as soon as a test fails.
   Instead, a file tests.sum (xtests.sum from "make xcheck") is generated,
diff --git a/nscd/nscd-client.h b/nscd/nscd-client.h
index c069bf6..ee16df6 100644
--- a/nscd/nscd-client.h
+++ b/nscd/nscd-client.h
@@ -240,12 +240,17 @@ static inline time_t
 datahead_init_common (struct datahead *head, nscd_ssize_t allocsize,
 		      nscd_ssize_t recsize, uint32_t ttl)
 {
+  /* Initialize so that we don't write out junk in uninitialized data to the
+     cache.  */
+  memset (head, 0, sizeof (*head));
+
   head->allocsize = allocsize;
   head->recsize = recsize;
   head->usable = true;
 
   head->ttl = ttl;
-  /* Compute the timeout time.  */
+
+  /* Compute and return the timeout time.  */
   return head->timeout = time (NULL) + ttl;
 }
 
@@ -253,18 +258,25 @@ static inline time_t
 datahead_init_pos (struct datahead *head, nscd_ssize_t allocsize,
 		   nscd_ssize_t recsize, uint8_t nreloads, uint32_t ttl)
 {
+  time_t ret = datahead_init_common (head, allocsize, recsize, ttl);
+
   head->notfound = false;
   head->nreloads = nreloads;
-  return datahead_init_common (head, allocsize, recsize, ttl);
+
+  return ret;
 }
 
 static inline time_t
 datahead_init_neg (struct datahead *head, nscd_ssize_t allocsize,
 		   nscd_ssize_t recsize, uint32_t ttl)
 {
+  time_t ret = datahead_init_common (head, allocsize, recsize, ttl);
+
+  /* We don't need to touch nreloads here since it is set to our desired value
+     (0) when we clear the structure.  */
   head->notfound = true;
-  head->nreloads = 0;
-  return datahead_init_common (head, allocsize, recsize, ttl);
+
+  return ret;
 }
 
 /* Structure for one hash table entry.  */