ipc: compat: use signed size_t types for msgsnd and msgrcv

The msgsnd and msgrcv system calls use size_t to represent the size of the
message being transferred.  POSIX states that values of msgsz greater than
SSIZE_MAX cause the result to be implementation-defined.  On Linux, this
equates to returning -EINVAL if (long) msgsz < 0.

For compat tasks where !CONFIG_ARCH_WANT_OLD_COMPAT_IPC and compat_size_t
is smaller than size_t, negative size values passed from userspace will be
interpreted as positive values by do_msg{rcv,snd} and will fail to exit
early with -EINVAL.

This patch changes the compat prototypes for msg{rcv,snd} so that the
message size is represented as a compat_ssize_t, which we cast to the
native ssize_t type for the core IPC code.

Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Chris Metcalf <cmetcalf@tilera.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 9f68e90a14e..f2b8fe20cc8 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -266,9 +266,9 @@ long compat_sys_shmat(int first, int second, compat_uptr_t third, int version,
 #else
 long compat_sys_semctl(int semid, int semnum, int cmd, int arg);
 long compat_sys_msgsnd(int msqid, struct compat_msgbuf __user *msgp,
-		size_t msgsz, int msgflg);
+		compat_ssize_t msgsz, int msgflg);
 long compat_sys_msgrcv(int msqid, struct compat_msgbuf __user *msgp,
-		size_t msgsz, long msgtyp, int msgflg);
+		compat_ssize_t msgsz, long msgtyp, int msgflg);
 long compat_sys_shmat(int shmid, compat_uptr_t shmaddr, int shmflg);
 #endif
 long compat_sys_msgctl(int first, int second, void __user *uptr);