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Date: Mon, 24 Jun 2024 18:36:59 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	linux-mips@...r.kernel.org,
	Helge Deller <deller@....de>,
	linux-parisc@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Andreas Larsson <andreas@...sler.com>,
	sparclinux@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org,
	Brian Cain <bcain@...cinc.com>,
	linux-hexagon@...r.kernel.org,
	Guo Ren <guoren@...nel.org>,
	linux-csky@...r.kernel.org,
	Heiko Carstens <hca@...ux.ibm.com>,
	linux-s390@...r.kernel.org,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	linux-sh@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org,
	libc-alpha@...rceware.org,
	musl@...ts.openwall.com,
	stable@...r.kernel.org
Subject: [PATCH v2 01/13] ftruncate: pass a signed offset

From: Arnd Bergmann <arnd@...db.de>

The old ftruncate() syscall, using the 32-bit off_t misses a sign
extension when called in compat mode on 64-bit architectures.  As a
result, passing a negative length accidentally succeeds in truncating
to file size between 2GiB and 4GiB.

Changing the type of the compat syscall to the signed compat_off_t
changes the behavior so it instead returns -EINVAL.

The native entry point, the truncate() syscall and the corresponding
loff_t based variants are all correct already and do not suffer
from this mistake.

Fixes: 3f6d078d4acc ("fix compat truncate/ftruncate")
Reviewed-by: Christian Brauner <brauner@...nel.org>
Cc: stable@...r.kernel.org
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/open.c                | 4 ++--
 include/linux/compat.h   | 2 +-
 include/linux/syscalls.h | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 89cafb572061..50e45bc7c4d8 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -202,13 +202,13 @@ long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
 	return error;
 }
 
-SYSCALL_DEFINE2(ftruncate, unsigned int, fd, unsigned long, length)
+SYSCALL_DEFINE2(ftruncate, unsigned int, fd, off_t, length)
 {
 	return do_sys_ftruncate(fd, length, 1);
 }
 
 #ifdef CONFIG_COMPAT
-COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_ulong_t, length)
+COMPAT_SYSCALL_DEFINE2(ftruncate, unsigned int, fd, compat_off_t, length)
 {
 	return do_sys_ftruncate(fd, length, 1);
 }
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 233f61ec8afc..56cebaff0c91 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -608,7 +608,7 @@ asmlinkage long compat_sys_fstatfs(unsigned int fd,
 asmlinkage long compat_sys_fstatfs64(unsigned int fd, compat_size_t sz,
 				     struct compat_statfs64 __user *buf);
 asmlinkage long compat_sys_truncate(const char __user *, compat_off_t);
-asmlinkage long compat_sys_ftruncate(unsigned int, compat_ulong_t);
+asmlinkage long compat_sys_ftruncate(unsigned int, compat_off_t);
 /* No generic prototype for truncate64, ftruncate64, fallocate */
 asmlinkage long compat_sys_openat(int dfd, const char __user *filename,
 				  int flags, umode_t mode);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 9104952d323d..ba9337709878 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -418,7 +418,7 @@ asmlinkage long sys_listmount(const struct mnt_id_req __user *req,
 			      u64 __user *mnt_ids, size_t nr_mnt_ids,
 			      unsigned int flags);
 asmlinkage long sys_truncate(const char __user *path, long length);
-asmlinkage long sys_ftruncate(unsigned int fd, unsigned long length);
+asmlinkage long sys_ftruncate(unsigned int fd, off_t length);
 #if BITS_PER_LONG == 32
 asmlinkage long sys_truncate64(const char __user *path, loff_t length);
 asmlinkage long sys_ftruncate64(unsigned int fd, loff_t length);
-- 
2.39.2

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