devmem: check vmalloc address on kmem read/write

Otherwise vmalloc_to_page() will BUG().

This also makes the kmem read/write implementation aligned with mem(4):
"References to nonexistent locations cause errors to be returned." Here we
return -ENXIO (inspired by Hugh) if no bytes have been transfered to/from
user space, otherwise return partial read/write results.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 10 deletions

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index be832b6f8279..1fd4b110d815 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -395,6 +395,7 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
         unsigned long p = *ppos;
         ssize_t low_count, read, sz;
         char * kbuf; /* k-addr because vread() takes vmlist_lock rwlock */
+        int err = 0;
 
         read = 0;
         if (p < (unsigned long) high_memory) {
@@ -441,12 +442,16 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
                         return -ENOMEM;
                 while (count > 0) {
                         sz = size_inside_page(p, count);
+                        if (!is_vmalloc_or_module_addr((void *)p)) {
+                                err = -ENXIO;
+                                break;
+                        }
                         sz = vread(kbuf, (char *)p, sz);
                         if (!sz)
                                 break;
                         if (copy_to_user(buf, kbuf, sz)) {
-                                free_page((unsigned long)kbuf);
-                                return -EFAULT;
+                                err = -EFAULT;
+                                break;
                         }
                         count -= sz;
                         buf += sz;
@@ -455,8 +460,8 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
                 }
                 free_page((unsigned long)kbuf);
         }
-        *ppos = p;
-        return read;
+        *ppos = p;
+        return read ? read : err;
 }
 
 
@@ -520,6 +525,7 @@ static ssize_t write_kmem(struct file * file, const char __user * buf,
         ssize_t wrote = 0;
         ssize_t virtr = 0;
         char * kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
+        int err = 0;
 
         if (p < (unsigned long) high_memory) {
                 unsigned long to_write = min_t(unsigned long, count,
@@ -540,12 +546,14 @@ static ssize_t write_kmem(struct file * file, const char __user * buf,
                         unsigned long sz = size_inside_page(p, count);
                         unsigned long n;
 
+                        if (!is_vmalloc_or_module_addr((void *)p)) {
+                                err = -ENXIO;
+                                break;
+                        }
                         n = copy_from_user(kbuf, buf, sz);
                         if (n) {
-                                if (wrote + virtr)
-                                        break;
-                                free_page((unsigned long)kbuf);
-                                return -EFAULT;
+                                err = -EFAULT;
+                                break;
                         }
                         sz = vwrite(kbuf, (char *)p, sz);
                         count -= sz;
@@ -556,8 +564,8 @@ static ssize_t write_kmem(struct file * file, const char __user * buf,
                 free_page((unsigned long)kbuf);
         }
 
-        *ppos = p;
-        return virtr + wrote;
+        *ppos = p;
+        return virtr + wrote ? : err;
 }
 #endif