From Richard Weinberger <> Subject [PATCH] Implement leftpad syscall Date Fri, 1 Apr 2016 00:33:32 +0200 From: David Gstir <david@sigma-star.at>



Implement the leftpad() system call such that userspace,

especially node.js applications, can in the near future directly

use it and no longer depend on fragile npm packages.



Signed-off-by: David Gstir <david@sigma-star.at>

Signed-off-by: Richard Weinberger <richard@nod.at>

---

arch/x86/entry/syscalls/syscall_64.tbl | 1 +

include/linux/syscalls.h | 1 +

kernel/sys.c | 35 ++++++++++++++++++++++++++++++++++

kernel/sys_ni.c | 1 +

4 files changed, 38 insertions(+)



diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl

index cac6d17..f287712 100644

--- a/arch/x86/entry/syscalls/syscall_64.tbl

+++ b/arch/x86/entry/syscalls/syscall_64.tbl

@@ -335,6 +335,7 @@

326 common copy_file_range sys_copy_file_range

327 64 preadv2 sys_preadv2

328 64 pwritev2 sys_pwritev2

+329 common leftpad sys_leftpad



#

# 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 d795472..a0850bb 100644

--- a/include/linux/syscalls.h

+++ b/include/linux/syscalls.h

@@ -898,4 +898,5 @@ asmlinkage long sys_copy_file_range(int fd_in, loff_t __user *off_in,



asmlinkage long sys_mlock2(unsigned long start, size_t len, int flags);



+asmlinkage long sys_leftpad(char *str, char pad, char *dst, size_t dst_len);

#endif

diff --git a/kernel/sys.c b/kernel/sys.c

index cf8ba54..e42d972 100644

--- a/kernel/sys.c

+++ b/kernel/sys.c

@@ -2432,3 +2432,38 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)

return 0;

}

#endif /* CONFIG_COMPAT */

+

+

+SYSCALL_DEFINE4(leftpad, char *, src, char, pad, char *, dst, size_t, dst_len)

+{

+ char *buf;

+ long ret;

+ size_t len = strlen_user(src);

+ size_t pad_len = dst_len - len;

+

+ if (dst_len <= len || dst_len > 4096) {

+ return -EINVAL;

+ }

+

+ buf = kmalloc(dst_len, GFP_KERNEL);

+ if (!buf)

+ return -ENOMEM;

+

+ memset(buf, pad, pad_len);

+ ret = copy_from_user(buf + pad_len, src, len);

+ if (ret) {

+ ret = -EFAULT;

+ goto out;

+ }

+

+ ret = copy_to_user(dst, buf, dst_len);

+ if (ret) {

+ ret = -EFAULT;

+ goto out;

+ }

+

+ ret = pad_len;

+out:

+ kfree(buf);

+ return ret;

+}

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c

index 2c5e3a8..262608d 100644

--- a/kernel/sys_ni.c

+++ b/kernel/sys_ni.c

@@ -175,6 +175,7 @@ cond_syscall(sys_setfsgid);

cond_syscall(sys_capget);

cond_syscall(sys_capset);

cond_syscall(sys_copy_file_range);

+cond_syscall(sys_leftpad);



/* arch-specific weak syscall entries */

cond_syscall(sys_pciconfig_read);

--

1.8.4.5

