[PATCH] reject corrupt swapfiles earlier

The fsfuzzer found this; with a corrupt small swapfile that claims to have
many pages:

  [root]# file swap.741.img
  swap.741.img: Linux/i386 swap file (new style) 1 (4K pages) size 1040191487 pages
  [root]# ls -l swap.741.img
  -rw-r--r-- 1 root root 16777216 Nov 22 05:18 swap.741.img

sys_swapon() will try to vmalloc all those pages, and -then- check to see if
the file is actually that large:

                if (!(p->swap_map = vmalloc(maxpages * sizeof(short)))) {
  <snip>
        if (swapfilesize && maxpages > swapfilesize) {
                printk(KERN_WARNING
                       "Swap area shorter than signature indicates\n");

It seems to me that it would make more sense to move this test up before
the vmalloc, with the other checks, to avoid the OOM-killer in this
situation...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 8e206cea0f5e..f315131db006 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1552,6 +1552,11 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
                 error = -EINVAL;
                 if (!maxpages)
                         goto bad_swap;
+                if (swapfilesize && maxpages > swapfilesize) {
+                        printk(KERN_WARNING
+                               "Swap area shorter than signature indicates\n");
+                        goto bad_swap;
+                }
                 if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
                         goto bad_swap;
                 if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
@@ -1579,12 +1584,6 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
                         goto bad_swap;
         }
 
-        if (swapfilesize && maxpages > swapfilesize) {
-                printk(KERN_WARNING
-                       "Swap area shorter than signature indicates\n");
-                error = -EINVAL;
-                goto bad_swap;
-        }
         if (nr_good_pages) {
                 p->swap_map[0] = SWAP_MAP_BAD;
                 p->max = maxpages;