Re: [PATCH v3 3/7] shm: add memfd_create() syscall

Signed-off-by: David Herrmann <redacted>
---
 arch/x86/syscalls/syscall_32.tbl |  1 +
 arch/x86/syscalls/syscall_64.tbl |  1 +
 include/linux/syscalls.h         |  1 +
 include/uapi/linux/memfd.h       |  8 +++++
 kernel/sys_ni.c                  |  1 +
 mm/shmem.c                       | 72 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 84 insertions(+)
 create mode 100644 include/uapi/linux/memfd.h

diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
index d6b8679..e7495b4 100644
--- a/arch/x86/syscalls/syscall_32.tbl
+++ b/arch/x86/syscalls/syscall_32.tbl

@@ -360,3 +360,4 @@
 351    i386    sched_setattr           sys_sched_setattr
 352    i386    sched_getattr           sys_sched_getattr
 353    i386    renameat2               sys_renameat2
+354    i386    memfd_create            sys_memfd_create

diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
index ec255a1..28be0e1 100644
--- a/arch/x86/syscalls/syscall_64.tbl
+++ b/arch/x86/syscalls/syscall_64.tbl

@@ -323,6 +323,7 @@
 314    common  sched_setattr           sys_sched_setattr
 315    common  sched_getattr           sys_sched_getattr
 316    common  renameat2               sys_renameat2
+317    common  memfd_create            sys_memfd_create

 #
 # x32-specific system call numbers start at 512 to avoid cache impact

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index b0881a0..0be5d4d 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -802,6 +802,7 @@ asmlinkage long sys_timerfd_settime(int ufd, int flags,
 asmlinkage long sys_timerfd_gettime(int ufd, struct itimerspec __user *otmr);
 asmlinkage long sys_eventfd(unsigned int count);
 asmlinkage long sys_eventfd2(unsigned int count, int flags);
+asmlinkage long sys_memfd_create(const char *uname_ptr, unsigned int flags);
 asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len);
 asmlinkage long sys_old_readdir(unsigned int, struct old_linux_dirent __user *, unsigned int);
 asmlinkage long sys_pselect6(int, fd_set __user *, fd_set __user *,

diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h
new file mode 100644
index 0000000..534e364
--- /dev/null
+++ b/include/uapi/linux/memfd.h

@@ -0,0 +1,8 @@
+#ifndef _UAPI_LINUX_MEMFD_H
+#define _UAPI_LINUX_MEMFD_H
+
+/* flags for memfd_create(2) (unsigned int) */
+#define MFD_CLOEXEC            0x0001U
+#define MFD_ALLOW_SEALING      0x0002U
+
+#endif /* _UAPI_LINUX_MEMFD_H */

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 36441b5..489a4e6 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c

@@ -197,6 +197,7 @@ cond_syscall(compat_sys_timerfd_settime);
 cond_syscall(compat_sys_timerfd_gettime);
 cond_syscall(sys_eventfd);
 cond_syscall(sys_eventfd2);
+cond_syscall(sys_memfd_create);

 /* performance counters: */
 cond_syscall(sys_perf_event_open);

diff --git a/mm/shmem.c b/mm/shmem.c
index 1438b3e..e7c5fe1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c

@@ -66,7 +66,9 @@ static struct vfsmount *shm_mnt;
 #include <linux/highmem.h>
 #include <linux/seq_file.h>
 #include <linux/magic.h>
+#include <linux/syscalls.h>
 #include <linux/fcntl.h>
+#include <uapi/linux/memfd.h>

 #include <asm/uaccess.h>
 #include <asm/pgtable.h>

@@ -2662,6 +2664,76 @@ static int shmem_show_options(struct seq_file *seq, struct dentry *root)
        shmem_show_mpol(seq, sbinfo->mpol);
        return 0;
 }
+
+#define MFD_NAME_PREFIX "memfd:"
+#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
+#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
+
+#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING)
+
+SYSCALL_DEFINE2(memfd_create,
+               const char*, uname,
+               unsigned int, flags)
+{
+       struct shmem_inode_info *info;
+       struct file *file;
+       int fd, error;
+       char *name;
+       long len;
+
+       if (flags & ~(unsigned int)MFD_ALL_FLAGS)
+               return -EINVAL;
+
+       /* length includes terminating zero */
+       len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
+       if (len <= 0)
+               return -EFAULT;
+       if (len > MFD_NAME_MAX_LEN + 1)
+               return -EINVAL;
+
+       name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_TEMPORARY);
+       if (!name)
+               return -ENOMEM;
+
+       strcpy(name, MFD_NAME_PREFIX);
+       if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
+               error = -EFAULT;
+               goto err_name;
+       }
+
+       /* terminating-zero may have changed after strnlen_user() returned */
+       if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
+               error = -EFAULT;
+               goto err_name;
+       }
+
+       fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
+       if (fd < 0) {
+               error = fd;
+               goto err_name;
+       }
+
+       file = shmem_file_setup(name, 0, VM_NORESERVE);
+       if (IS_ERR(file)) {
+               error = PTR_ERR(file);
+               goto err_fd;
+       }
+       info = SHMEM_I(file_inode(file));
+       file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
+       if (flags & MFD_ALLOW_SEALING)
+               info->seals &= ~F_SEAL_SEAL;
+
+       fd_install(fd, file);
+       kfree(name);
+       return fd;
+
+err_fd:
+       put_unused_fd(fd);
+err_name:
+       kfree(name);
+       return error;
+}
+
 #endif /* CONFIG_TMPFS */

 static void shmem_put_super(struct super_block *sb)
--

2.0.0