From: Hao Lee <haolee.swjtu@xxxxxxxxx>
Subject: 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
[akpm@xxxxxxxxxxxxxxxxxxxx: remove now-unneeded cast]
Link: https://lkml.kernel.org/r/Ye1fCxyZZ0I5lgOL@localhost.localdomain
Signed-off-by: Hao Lee <haolee.swjtu@xxxxxxxxx>
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: James Morris <jamorris@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- a/fs/proc/base.c~proc-alloc-path_max-bytes-for-proc-pid-fd-symlinks
+++ a/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;
}
_
