nss_compat: internal_end*ent may clobber errno, hiding ERANGE [BZ #25976]

During cleanup, before returning from get*_r functions, the end*ent
calls must not change errno.  Otherwise, an ERANGE error from the
underlying implementation can be hidden, causing unexpected lookup
failures.  This commit introduces an internal_end*ent_noerror
function which saves and restore errno, and marks the original
internal_end*ent function as warn_unused_result, so that it is used
only in contexts were errors from it can be handled explicitly.

Reviewed-by: DJ Delorie <dj@redhat.com>
(cherry picked from commit 790b8dda4455865cb8c3a47801f4304c1a43baf6)
(cherry picked from commit 3a44844c97a8ca1d0798c45b5252e6a49f9cf8e1)

5 files changed, 47 insertions, 11 deletions

diff --git a/NEWS b/NEWS
index 9bfd01ccb1..24371e5745 100644
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,7 @@ The following bugs are resolved with this release:
   [25896] Incorrect prctl
   [25902] Bad LOADARGS_N
   [25966] Incorrect access of __x86_shared_non_temporal_threshold for x32
+  [25976] nss_compat: internal_end*ent may clobber errno, hiding ERANGE
 
 Security related changes:
 
diff --git a/nss/nss_compat/compat-grp.c b/nss/nss_compat/compat-grp.c
index a8de1e03b3..f8b19a5cf0 100644
--- a/nss/nss_compat/compat-grp.c
+++ b/nss/nss_compat/compat-grp.c
@@ -142,7 +142,7 @@ _nss_compat_setgrent (int stayopen)
 }
 
 
-static enum nss_status
+static enum nss_status __attribute_warn_unused_result__
 internal_endgrent (ent_t *ent)
 {
   if (ent->stream != NULL)
@@ -163,6 +163,15 @@ internal_endgrent (ent_t *ent)
   return NSS_STATUS_SUCCESS;
 }
 
+/* Like internal_endgrent, but preserve errno in all cases.  */
+static void
+internal_endgrent_noerror (ent_t *ent)
+{
+  int saved_errno = errno;
+  enum nss_status unused __attribute__ ((unused)) = internal_endgrent (ent);
+  __set_errno (saved_errno);
+}
+
 enum nss_status
 _nss_compat_endgrent (void)
 {
@@ -483,7 +492,7 @@ _nss_compat_getgrnam_r (const char *name, struct group *grp,
   if (result == NSS_STATUS_SUCCESS)
     result = internal_getgrnam_r (name, grp, &ent, buffer, buflen, errnop);
 
-  internal_endgrent (&ent);
+  internal_endgrent_noerror (&ent);
 
   return result;
 }
@@ -612,7 +621,7 @@ _nss_compat_getgrgid_r (gid_t gid, struct group *grp,
   if (result == NSS_STATUS_SUCCESS)
     result = internal_getgrgid_r (gid, grp, &ent, buffer, buflen, errnop);
 
-  internal_endgrent (&ent);
+  internal_endgrent_noerror (&ent);
 
   return result;
 }
diff --git a/nss/nss_compat/compat-initgroups.c b/nss/nss_compat/compat-initgroups.c
index 939b25b33b..7591442ff9 100644
--- a/nss/nss_compat/compat-initgroups.c
+++ b/nss/nss_compat/compat-initgroups.c
@@ -133,7 +133,7 @@ internal_setgrent (ent_t *ent)
 }
 
 
-static enum nss_status
+static enum nss_status __attribute_warn_unused_result__
 internal_endgrent (ent_t *ent)
 {
   if (ent->stream != NULL)
@@ -157,6 +157,15 @@ internal_endgrent (ent_t *ent)
   return NSS_STATUS_SUCCESS;
 }
 
+/* Like internal_endgrent, but preserve errno in all cases.  */
+static void
+internal_endgrent_noerror (ent_t *ent)
+{
+  int saved_errno = errno;
+  enum nss_status unused __attribute__ ((unused)) = internal_endgrent (ent);
+  __set_errno (saved_errno);
+}
+
 /* Add new group record.  */
 static void
 add_group (long int *start, long int *size, gid_t **groupsp, long int limit,
@@ -501,7 +510,7 @@ _nss_compat_initgroups_dyn (const char *user, gid_t group, long int *start,
  done:
   scratch_buffer_free (&tmpbuf);
 
-  internal_endgrent (&intern);
+  internal_endgrent_noerror (&intern);
 
   return status;
 }
diff --git a/nss/nss_compat/compat-pwd.c b/nss/nss_compat/compat-pwd.c
index ec3f35c594..bd5e707da0 100644
--- a/nss/nss_compat/compat-pwd.c
+++ b/nss/nss_compat/compat-pwd.c
@@ -259,7 +259,7 @@ _nss_compat_setpwent (int stayopen)
 }
 
 
-static enum nss_status
+static enum nss_status __attribute_warn_unused_result__
 internal_endpwent (ent_t *ent)
 {
   if (ent->stream != NULL)
@@ -287,6 +287,15 @@ internal_endpwent (ent_t *ent)
   return NSS_STATUS_SUCCESS;
 }
 
+/* Like internal_endpwent, but preserve errno in all cases.  */
+static void
+internal_endpwent_noerror (ent_t *ent)
+{
+  int saved_errno = errno;
+  enum nss_status unused __attribute__ ((unused)) = internal_endpwent (ent);
+  __set_errno (saved_errno);
+}
+
 enum nss_status
 _nss_compat_endpwent (void)
 {
@@ -822,7 +831,7 @@ _nss_compat_getpwnam_r (const char *name, struct passwd *pwd,
   if (result == NSS_STATUS_SUCCESS)
     result = internal_getpwnam_r (name, pwd, &ent, buffer, buflen, errnop);
 
-  internal_endpwent (&ent);
+  internal_endpwent_noerror (&ent);
 
   return result;
 }
@@ -1061,7 +1070,7 @@ _nss_compat_getpwuid_r (uid_t uid, struct passwd *pwd,
   if (result == NSS_STATUS_SUCCESS)
     result = internal_getpwuid_r (uid, pwd, &ent, buffer, buflen, errnop);
 
-  internal_endpwent (&ent);
+  internal_endpwent_noerror (&ent);
 
   return result;
 }
diff --git a/nss/nss_compat/compat-spwd.c b/nss/nss_compat/compat-spwd.c
index f6b7a1ef15..d0e3c51b45 100644
--- a/nss/nss_compat/compat-spwd.c
+++ b/nss/nss_compat/compat-spwd.c
@@ -215,7 +215,7 @@ _nss_compat_setspent (int stayopen)
 }
 
 
-static enum nss_status
+static enum nss_status __attribute_warn_unused_result__
 internal_endspent (ent_t *ent)
 {
   if (ent->stream != NULL)
@@ -244,6 +244,15 @@ internal_endspent (ent_t *ent)
   return NSS_STATUS_SUCCESS;
 }
 
+/* Like internal_endspent, but preserve errno in all cases.  */
+static void
+internal_endspent_noerror (ent_t *ent)
+{
+  int saved_errno = errno;
+  enum nss_status unused __attribute__ ((unused)) = internal_endspent (ent);
+  __set_errno (saved_errno);
+}
+
 enum nss_status
 _nss_compat_endspent (void)
 {
@@ -261,7 +270,6 @@ _nss_compat_endspent (void)
   return result;
 }
 
-
 static enum nss_status
 getspent_next_nss_netgr (const char *name, struct spwd *result, ent_t *ent,
 			 char *group, char *buffer, size_t buflen,
@@ -786,7 +794,7 @@ _nss_compat_getspnam_r (const char *name, struct spwd *pwd,
   if (result == NSS_STATUS_SUCCESS)
     result = internal_getspnam_r (name, pwd, &ent, buffer, buflen, errnop);
 
-  internal_endspent (&ent);
+  internal_endspent_noerror (&ent);
 
   return result;
 }