[PATCH v2 01/13] ftruncate: pass a signed offset

Arnd Bergmann
2024-06-24T16:37:26Z

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@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.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