[PATCH] Implement leftpad syscall

Richard Weinberger
2016-03-31T22:33:58Z

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