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Date: Thu, 20 Jun 2024 18:23:02 +0200
From: Arnd Bergmann <>
Cc: Arnd Bergmann <>,
	Thomas Bogendoerfer <>,,
	Helge Deller <>,,
	"David S. Miller" <>,
	Andreas Larsson <>,,
	Michael Ellerman <>,
	Nicholas Piggin <>,
	Christophe Leroy <>,
	"Naveen N . Rao" <>,,
	Brian Cain <>,,
	Guo Ren <>,,
	Heiko Carstens <>,,
	Rich Felker <>,
	John Paul Adrian Glaubitz <>,,
	"H. Peter Anvin" <>,
	Alexander Viro <>,
	Christian Brauner <>,,,,,
Subject: [PATCH 01/15] ftruncate: pass a signed offset

From: Arnd Bergmann <>

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")
Signed-off-by: Arnd Bergmann <>
 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);
-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);

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