[Linux PATCH] fcntl: add new F_OFD_*32 constants and handle them appropriately

[Jeff Layton <jlayton@redhat.com>]

When I originally added OFD lock support, we made the assumption that
userland would always pass in a struct flock64 for an OFD lock. It's
possible however for someone to build a binary without large file
support (aka LFS), which will call down into the kernel with the
standard F_OFD_* constants, but pass in a "legacy" struct flock.

My first thought was to patch glibc to cause a build break if anyone
tries to use OFD locks without LFS, but now I think it might be less
problematic to simply support OFD locks without LFS enabled.

The kernel handles this for classic POSIX locks with a separate set of
constants (postfixed with "64") to indicate that the incoming structure
is an LFS one. We can't do that here since the kernel already assumes
that the structure is an LFS one.

Instead, we can define a new set of constants that are postfixed with
"32" to indicate that the incoming structure is a non-LFS one. This
patch adds the kernel plumbing to handle that case. We'll also need a
small patch for glibc to make it to use these constants when LFS is
disabled.

In the event that someone builds a program with a new glibc, and runs it
on a kernel without support for F_OFD_*32 constants, they will just get
back EINVAL. That's preferable to the current situation which is
undefined behavior due to misinterpretation of the struct flock
argument.

Cc: stable@vger.kernel.org	# v3.15+
Reported-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/compat.c                      | 3 +++
 fs/fcntl.c                       | 4 +++-
 fs/locks.c                       | 4 +++-
 include/uapi/asm-generic/fcntl.h | 4 ++++
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/compat.c b/fs/compat.c
index be6e48b0a46c..a7e9640e9107 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -426,6 +426,9 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd, unsigned int, cmd,
 	case F_GETLK:
 	case F_SETLK:
 	case F_SETLKW:
+	case F_OFD_GETLK32:
+	case F_OFD_SETLK32:
+	case F_OFD_SETLKW32:
 		ret = get_compat_flock(&f, compat_ptr(arg));
 		if (ret != 0)
 			break;
diff --git a/fs/fcntl.c b/fs/fcntl.c
index 350a2c8cfd28..71704aa11170 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -270,6 +270,7 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 	/* 32-bit arches must use fcntl64() */
 	case F_OFD_GETLK:
 #endif
+	case F_OFD_GETLK32:
 	case F_GETLK:
 		err = fcntl_getlk(filp, cmd, (struct flock __user *) arg);
 		break;
@@ -278,7 +279,8 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 	case F_OFD_SETLK:
 	case F_OFD_SETLKW:
 #endif
-		/* Fallthrough */
+	case F_OFD_SETLK32:
+	case F_OFD_SETLKW32:
 	case F_SETLK:
 	case F_SETLKW:
 		err = fcntl_setlk(fd, filp, cmd, (struct flock __user *) arg);
diff --git a/fs/locks.c b/fs/locks.c
index 7e428b78be07..4ffde68322de 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2065,7 +2065,7 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock __user *l)
 	if (error)
 		goto out;
 
-	if (cmd == F_OFD_GETLK) {
+	if (cmd == F_OFD_GETLK || cmd == F_OFD_GETLK32) {
 		error = -EINVAL;
 		if (flock.l_pid != 0)
 			goto out;
@@ -2222,6 +2222,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
 	 */
 	switch (cmd) {
 	case F_OFD_SETLK:
+	case F_OFD_SETLK32:
 		error = -EINVAL;
 		if (flock.l_pid != 0)
 			goto out;
@@ -2231,6 +2232,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
 		file_lock->fl_owner = filp;
 		break;
 	case F_OFD_SETLKW:
+	case F_OFD_SETLKW32:
 		error = -EINVAL;
 		if (flock.l_pid != 0)
 			goto out;
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index e063effe0cc1..b407deee68e1 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -148,6 +148,10 @@
 #define F_OFD_SETLK	37
 #define F_OFD_SETLKW	38
 
+#define F_OFD_GETLK32	39
+#define F_OFD_SETLK32	40
+#define F_OFD_SETLKW32	41
+
 #define F_OWNER_TID	0
 #define F_OWNER_PID	1
 #define F_OWNER_PGRP	2
-- 
2.7.4