linux-kernel - Re: BUG: unable to handle kernel paging request at virtual address

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 5 Jan 2008 09:10:12 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Alexander Shaduri <ashaduri@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel paging request at virtual address

On Fri, Jan 04, 2008 at 09:38:12PM +0400, Alexander Shaduri wrote:
> 
> I got the following message, shortly followed by a system hang.
> BUG: unable to handle kernel paging request at virtual address 48464443
> 
> (see the oops below).

AFAICS, it's quicklist_alloc() called from pgd_alloc():

static inline void *quicklist_alloc(int nr, gfp_t flags, void (*ctor)(void *))
{
        struct quicklist *q;
        void **p = NULL;

        q =&get_cpu_var(quicklist)[nr];
        p = q->page;
        if (likely(p)) {
                q->page = p[0];

and we have q->page == 0x48464443.  Seeing how we assign that sucker, that
smells like we've got a page on quicklist with {0x43, 0x44, 0x46, 0x48}
in its first 4 bytes.  Instead of having address of the next page stored
in there...

Do other oopsen of the same kind give the same value?  The shortest
scenario I can see for that is
	* something accidentally frees a page
	* pgd_alloc() grabs it
	* pgd_free() releases it and puts on quicklist; the first 4 bytes
are zeroed.
	* whatever used to hold that page modifies it, overwriting its
beginning
	* next pgd_alloc() grabs that page and advances quicklist - sets
it to the first 4 bytes of that page.  At that point we are well and truly
fucked - quicklist is corrupted and once we need more pgd we'll get that
oops.

The question is, what's losing and then overwriting that page in the
first place?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/