linux-kernel - [PATCH v4 1/2] mm/memfd: Refactor and cleanup the logic in memfd

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Message-ID: <20250110165904.3437374-2-isaacmanjarres@google.com>
Date: Fri, 10 Jan 2025 08:58:59 -0800
From: "Isaac J. Manjarres" <isaacmanjarres@...gle.com>
To: lorenzo.stoakes@...cle.com, Andrew Morton <akpm@...ux-foundation.org>
Cc: kaleshsingh@...gle.com, jstultz@...gle.com, aliceryhl@...gle.com, 
	surenb@...gle.com, "Isaac J. Manjarres" <isaacmanjarres@...gle.com>, kernel-team@...roid.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/2] mm/memfd: Refactor and cleanup the logic in memfd_create()

memfd_create() is a pretty busy function that could be easier to read
if some of the logic was split out into helper functions.

Therefore, split the flags sanitization, name allocation, and file
structure allocation into their own helper functions.

No functional change.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
---
 mm/memfd.c | 81 ++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 58 insertions(+), 23 deletions(-)

diff --git a/mm/memfd.c b/mm/memfd.c
index 5f5a23c9051d..04d9e2a23df8 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -369,15 +369,9 @@ int memfd_check_seals_mmap(struct file *file, unsigned long *vm_flags_ptr)
 	return err;
 }
 
-SYSCALL_DEFINE2(memfd_create,
-		const char __user *, uname,
-		unsigned int, flags)
+static int sanitize_flags(unsigned int *flags_ptr)
 {
-	unsigned int *file_seals;
-	struct file *file;
-	int fd, error;
-	char *name;
-	long len;
+	unsigned int flags = *flags_ptr;
 
 	if (!(flags & MFD_HUGETLB)) {
 		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
@@ -393,20 +387,25 @@ SYSCALL_DEFINE2(memfd_create,
 	if ((flags & MFD_EXEC) && (flags & MFD_NOEXEC_SEAL))
 		return -EINVAL;
 
-	error = check_sysctl_memfd_noexec(&flags);
-	if (error < 0)
-		return error;
+	return check_sysctl_memfd_noexec(flags_ptr);
+}
+
+static char *alloc_name(const char __user *uname)
+{
+	int error;
+	char *name;
+	long len;
 
 	/* length includes terminating zero */
 	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
 	if (len <= 0)
-		return -EFAULT;
+		return ERR_PTR(-EFAULT);
 	if (len > MFD_NAME_MAX_LEN + 1)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
 
 	name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
 	if (!name)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	strcpy(name, MFD_NAME_PREFIX);
 	if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
@@ -420,23 +419,28 @@ SYSCALL_DEFINE2(memfd_create,
 		goto err_name;
 	}
 
-	fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
-	if (fd < 0) {
-		error = fd;
-		goto err_name;
-	}
+	return name;
+
+err_name:
+	kfree(name);
+	return ERR_PTR(error);
+}
+
+static struct file *alloc_file(const char *name, unsigned int flags)
+{
+	unsigned int *file_seals;
+	struct file *file;
 
 	if (flags & MFD_HUGETLB) {
 		file = hugetlb_file_setup(name, 0, VM_NORESERVE,
 					HUGETLB_ANONHUGE_INODE,
 					(flags >> MFD_HUGE_SHIFT) &
 					MFD_HUGE_MASK);
-	} else
+	} else {
 		file = shmem_file_setup(name, 0, VM_NORESERVE);
-	if (IS_ERR(file)) {
-		error = PTR_ERR(file);
-		goto err_fd;
 	}
+	if (IS_ERR(file))
+		return file;
 	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
 	file->f_flags |= O_LARGEFILE;
 
@@ -456,6 +460,37 @@ SYSCALL_DEFINE2(memfd_create,
 			*file_seals &= ~F_SEAL_SEAL;
 	}
 
+	return file;
+}
+
+SYSCALL_DEFINE2(memfd_create,
+		const char __user *, uname,
+		unsigned int, flags)
+{
+	struct file *file;
+	int fd, error;
+	char *name;
+
+	error = sanitize_flags(&flags);
+	if (error < 0)
+		return error;
+
+	name = alloc_name(uname);
+	if (IS_ERR(name))
+		return PTR_ERR(name);
+
+	fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
+	if (fd < 0) {
+		error = fd;
+		goto err_name;
+	}
+
+	file = alloc_file(name, flags);
+	if (IS_ERR(file)) {
+		error = PTR_ERR(file);
+		goto err_fd;
+	}
+
 	fd_install(fd, file);
 	kfree(name);
 	return fd;
-- 
2.47.1.613.gc27f4b7a9f-goog