proc: alloc PATH_MAX bytes for /proc/${pid}/fd/ symlinks

It's not a standard approach that use __get_free_page() to alloc path
buffer directly.  We'd better use kmalloc and PATH_MAX.

	PAGE_SIZE is different on different archs. An unlinked file
	with very long canonical pathname will readlink differently
	because "(deleted)" eats into a buffer.	--adobriyan

[[email protected]: remove now-unneeded cast]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Hao Lee <[email protected]>
Signed-off-by: Alexey Dobriyan <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: James Morris <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index d654ce7150fd..76bf1aa3cfe8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1764,25 +1764,25 @@ out:
 
 static int do_proc_readlink(struct path *path, char __user *buffer, int buflen)
 {
-	char *tmp = (char *)__get_free_page(GFP_KERNEL);
+	char *tmp = kmalloc(PATH_MAX, GFP_KERNEL);
 	char *pathname;
 	int len;
 
 	if (!tmp)
 		return -ENOMEM;
 
-	pathname = d_path(path, tmp, PAGE_SIZE);
+	pathname = d_path(path, tmp, PATH_MAX);
 	len = PTR_ERR(pathname);
 	if (IS_ERR(pathname))
 		goto out;
-	len = tmp + PAGE_SIZE - 1 - pathname;
+	len = tmp + PATH_MAX - 1 - pathname;
 
 	if (len > buflen)
 		len = buflen;
 	if (copy_to_user(buffer, pathname, len))
 		len = -EFAULT;
  out:
-	free_page((unsigned long)tmp);
+	kfree(tmp);
 	return len;
 }