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Subject[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>

Index: linux-2.6.18/mm/swapfile.c
===================================================================
--- linux-2.6.18.orig/mm/swapfile.c
+++ linux-2.6.18/mm/swapfile.c
@@ -1544,6 +1544,11 @@ asmlinkage long sys_swapon(const char __
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)
@@ -1571,12 +1576,6 @@ asmlinkage long sys_swapon(const char __
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;
-
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