[PATCH] linux: Clear mode_t padding bits (BZ#25623)

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

The kernel might not clear the padding value for the ipc_perm mode
fields in compat mode (32 bit running on a 64 bit kernel).  It was
fixed on v4.14 when the ipc compat code was refactored to move
(commits 553f770ef71b, 469391684626, c0ebccb6fa1e).

Although it is most likely a kernel issue, it was shown only due
BZ#18231 fix which made all the SysVIPC mode_t 32-bit regardless of
the kABI.

This patch fixes it by explicit zeroing the upper bits for such
cases.  The __ASSUME_SYSVIPC_BROKEN_MODE_T case already handles
it with the shift.

(The aarch64 ipc_priv.h is superflous since
__ASSUME_SYSVIPC_DEFAULT_IPC_64 is now defined as default).

Checked on i686-linux-gnu on 3.10 and on 4.15 kernel.
---
 sysdeps/unix/sysv/linux/aarch64/ipc_priv.h | 21 ---------------------
 sysdeps/unix/sysv/linux/msgctl.c           |  9 +++++++--
 sysdeps/unix/sysv/linux/semctl.c           |  9 +++++++--
 sysdeps/unix/sysv/linux/shmctl.c           |  9 +++++++--
 4 files changed, 21 insertions(+), 27 deletions(-)
 delete mode 100644 sysdeps/unix/sysv/linux/aarch64/ipc_priv.h

diff --git a/sysdeps/unix/sysv/linux/aarch64/ipc_priv.h b/sysdeps/unix/sysv/linux/aarch64/ipc_priv.h
deleted file mode 100644
index 07a1c3a7d3..0000000000
--- a/sysdeps/unix/sysv/linux/aarch64/ipc_priv.h
+++ /dev/null
@@ -1,21 +0,0 @@
-/* Old SysV permission definition for Linux.  AArch64 version.
-   Copyright (C) 2016-2020 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <https://www.gnu.org/licenses/>.  */
-
-#include <sys/ipc.h>  /* For __key_t  */
-
-#define __IPC_64	0x0
diff --git a/sysdeps/unix/sysv/linux/msgctl.c b/sysdeps/unix/sysv/linux/msgctl.c
index 27879e76cd..48801a3fba 100644
--- a/sysdeps/unix/sysv/linux/msgctl.c
+++ b/sysdeps/unix/sysv/linux/msgctl.c
@@ -61,7 +61,6 @@ __new_msgctl (int msqid, int cmd, struct msqid_ds *buf)
 
   int ret = msgctl_syscall (msqid, cmd, buf);
 
-#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
   if (ret >= 0)
     {
       switch (cmd)
@@ -69,10 +68,16 @@ __new_msgctl (int msqid, int cmd, struct msqid_ds *buf)
 	case IPC_STAT:
 	case MSG_STAT:
 	case MSG_STAT_ANY:
+#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
 	  buf->msg_perm.mode >>= 16;
+#else
+	  /* Old Linux kernel versions might not clear the mode padding.  */
+	  if (sizeof ((struct msqid_ds){0}.msg_perm.mode
+	      != sizeof ((struct __old_ipc_perm){0}.mode)))
+	    buf->msg_perm.mode &= 0xFFFF;
+#endif
 	}
     }
-#endif
 
   return ret;
 }
diff --git a/sysdeps/unix/sysv/linux/semctl.c b/sysdeps/unix/sysv/linux/semctl.c
index 0c3eb0932f..580a72febe 100644
--- a/sysdeps/unix/sysv/linux/semctl.c
+++ b/sysdeps/unix/sysv/linux/semctl.c
@@ -92,7 +92,6 @@ __new_semctl (int semid, int semnum, int cmd, ...)
 
   int ret = semctl_syscall (semid, semnum, cmd, arg);
 
-#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
   if (ret >= 0)
     {
       switch (cmd)
@@ -100,10 +99,16 @@ __new_semctl (int semid, int semnum, int cmd, ...)
         case IPC_STAT:
         case SEM_STAT:
         case SEM_STAT_ANY:
+#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
           arg.buf->sem_perm.mode >>= 16;
+#else
+	  /* Old Linux kernel versions might not clear the mode padding.  */
+	  if (sizeof ((struct semid_ds){0}.sem_perm.mode
+	      != sizeof ((struct __old_ipc_perm){0}.mode)))
+	    arg.buf->sem_perm.mode &= 0xFFFF;
+#endif
 	}
     }
-#endif
 
   return ret;
 }
diff --git a/sysdeps/unix/sysv/linux/shmctl.c b/sysdeps/unix/sysv/linux/shmctl.c
index 39fa861e17..9a44ad6920 100644
--- a/sysdeps/unix/sysv/linux/shmctl.c
+++ b/sysdeps/unix/sysv/linux/shmctl.c
@@ -63,7 +63,6 @@ __new_shmctl (int shmid, int cmd, struct shmid_ds *buf)
 
   int ret = shmctl_syscall (shmid, cmd, buf);
 
-#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
   if (ret >= 0)
     {
       switch (cmd)
@@ -71,10 +70,16 @@ __new_shmctl (int shmid, int cmd, struct shmid_ds *buf)
         case IPC_STAT:
         case SHM_STAT:
         case SHM_STAT_ANY:
+#ifdef __ASSUME_SYSVIPC_BROKEN_MODE_T
           buf->shm_perm.mode >>= 16;
+#else
+	  /* Old Linux kernel versions might not clear the mode padding.  */
+	  if (sizeof ((struct shmid_ds){0}.shm_perm.mode)
+	      != sizeof ((struct __old_ipc_perm){0}.mode))
+	    buf->shm_perm.mode &= 0xFFFF;
+#endif
 	}
     }
-#endif
 
   return ret;
 }
-- 
2.17.1