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mm/memfd: refactor and cleanup the logic in memfd_create()

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Patch series "Cleanup for memfd_create()", v4.

memfd_create() handles all of its logic in a single function.  Some of the
logic in the function is also somewhat contrived (i.e.  copying the memfd
name from userpace).

This series aims to cleanup memfd_create() by splitting out the logic into
helper functions, and simplifying the memfd name copying to make the code
easier to follow.

This has no intended functional changes.

Thank you Alice and Lorenzo for reviewing v3 of this series and for your
feedback!


This patch (of 2):

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.

Link: https://lkml.kernel.org/r/20250110165904.3437374-1-isaacmanjarres@google.com
Link: https://lkml.kernel.org/r/20250110165904.3437374-2-isaacmanjarres@google.com
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Isaac J. Manjarres <isaacmanjarres@google.com>
Cc: John Stultz <jstultz@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Isaac J. Manjarres 2025-01-10 08:58:59 -08:00 committed by Andrew Morton
parent d783cc5913
commit f5dbcd90da
1 changed files with 58 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

81
mm/memfd.c
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@ -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;