exec: open code copy_string_kernel

Currently copy_string_kernel is just a wrapper around copy_strings that
simplifies the calling conventions and uses set_fs to allow passing a
kernel pointer.  But due to the fact the we only need to handle a single
kernel argument pointer, the logic can be sigificantly simplified while
getting rid of the set_fs.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Link: http://lkml.kernel.org/r/20200501104105.2621149-3-hch@lst.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/exec.c b/fs/exec.c
index 4814b26a56fbb0b664b5112dd4990b052f3587fb..03a85e3c49bbfa54c51864f11948969c917494f6 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -592,17 +592,42 @@ out:
  */
 int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
 {
-       int r;
-       mm_segment_t oldfs = get_fs();
-       struct user_arg_ptr argv = {
-               .ptr.native = (const char __user *const  __user *)&arg,
-       };
+       int len = strnlen(arg, MAX_ARG_STRLEN) + 1 /* terminating NUL */;
+       unsigned long pos = bprm->p;
+
+       if (len == 0)
+               return -EFAULT;
+       if (!valid_arg_len(bprm, len))
+               return -E2BIG;
+
+       /* We're going to work our way backwards. */
+       arg += len;
+       bprm->p -= len;
+       if (IS_ENABLED(CONFIG_MMU) && bprm->p < bprm->argmin)
+               return -E2BIG;
+
+       while (len > 0) {
+               unsigned int bytes_to_copy = min_t(unsigned int, len,
+                               min_not_zero(offset_in_page(pos), PAGE_SIZE));
+               struct page *page;
+               char *kaddr;
 
-       set_fs(KERNEL_DS);
-       r = copy_strings(1, argv, bprm);
-       set_fs(oldfs);
+               pos -= bytes_to_copy;
+               arg -= bytes_to_copy;
+               len -= bytes_to_copy;
 
-       return r;
+               page = get_arg_page(bprm, pos, 1);
+               if (!page)
+                       return -E2BIG;
+               kaddr = kmap_atomic(page);
+               flush_arg_page(bprm, pos & PAGE_MASK, page);
+               memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
+               flush_kernel_dcache_page(page);
+               kunmap_atomic(kaddr);
+               put_arg_page(page);
+       }
+
+       return 0;
 }
 EXPORT_SYMBOL(copy_string_kernel);