CVE-2023-52739

In the Linux kernel, the following vulnerability has been resolved:

Fix page corruption caused by racy check in _freepages

When we upgraded our kernel, we started seeing some page corruption like the following consistently:

BUG: Bad page state in process ganesha.nfsd pfn:1304ca page:0000000022261c55 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x0 pfn:0x1304ca flags: 0x17ffffc0000000() raw: 0017ffffc0000000 ffff8a513ffd4c98 ffffeee24b35ec08 0000000000000000 raw: 0000000000000000 0000000000000001 00000000ffffff7f 0000000000000000 page dumped because: nonzero mapcount CPU: 0 PID: 15567 Comm: ganesha.nfsd Kdump: loaded Tainted: P B O 5.10.158-1.nutanix.20221209.el7.x8664 #1 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 04/05/2016 Call Trace: dumpstack+0x74/0x96 badpage.cold+0x63/0x94 checknewpagebad+0x6d/0x80 rmqueue+0x46e/0x970 getpagefrom_freelist+0xcb/0x3f0 ? condresched+0x19/0x40 _allocpagesnodemask+0x164/0x300 allocpagescurrent+0x87/0xf0 skbpagefragrefill+0x84/0x110 ...

Sometimes, it would also show up as corruption in the free list pointer and cause crashes.

After bisecting the issue, we found the issue started from commit e320d3012d25 ("mm/page_alloc.c: fix freeing non-compound pages"):

if (put_page_testzero(page))
    free_the_page(page, order);
else if (!PageHead(page))
    while (order-- > 0)
        free_the_page(page + (1 << order), order);

So the problem is the check PageHead is racy because at this point we already dropped our reference to the page. So even if we came in with compound page, the page can already be freed and PageHead can return false and we will end up freeing all the tail pages causing double free.