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SubjectRe: keys: GPF in request_key
On Wed, Feb 1, 2017 at 3:54 PM, David Howells <dhowells@redhat.com> wrote:
> Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> > Can you disassemble this function for me? There are several possible paths
>> > and without the argument to the syscall and whether there's a key that was
>> > matched, it's hard to say which path is being taken - but this might help
>> > determine that.
>>
>> Here it is:
>> https://gist.githubusercontent.com/dvyukov/65efc41d00ef0033f9374853b9265c71/raw/9d8540dfb199b81f3d3534ec4cc6da378d07f5b2/gistfile1.txt
>
> Okay, it's called from here:
>
> ffffffff820490fd: lea -0x1b0(%rbp),%rdi
> ffffffff82049104: callq ffffffff82047800 <construct_get_dest_keyring>
> ffffffff82049109: mov -0x1b0(%rbp),%rdi
> ffffffff82049110: mov %r15,%rsi
> ffffffff82049113: callq ffffffff8203efd0 <key_link> <---
> ffffffff82049118: mov -0x1b0(%rbp),%rdi
> ffffffff8204911f: mov %eax,%r14d
> ffffffff82049122: callq ffffffff82037ab0 <key_put>
>
> Which should correspond to this:
>
> key_ref = search_process_keyrings(&ctx);
>
> if (!IS_ERR(key_ref)) {
> key = key_ref_to_ptr(key_ref);
> if (dest_keyring) {
> construct_get_dest_keyring(&dest_keyring);
> ret = key_link(dest_keyring, key); <---
> key_put(dest_keyring);
> if (ret < 0) {
> key_put(key);
> key = ERR_PTR(ret);
> goto error_free;
> }
> }
>
> which means that the search was successful, the requested key already exists
> and there was a destination keyring nominated by userspace. The first
> conditional clause of construct_get_dest_keyring() must've been true:
>
> struct key *dest_keyring = *_dest_keyring
> ...
> if (dest_keyring) {
> /* the caller supplied one */
> key_get(dest_keyring);
> } else {
>
> because it matches the containing if-condition in the calling function.
>
>> I actually know what were the arguments to the syscall. Since it
>> happened in a user process context, I know what syzkaller program it
>> was running at the time of the crash. It's just they are not
>> reproducible. Here are the 3 programs, and they are almost equivalent
>> as far as I can see. It's in syzkaller format, but I hope you can
>> decipher it, it's just syscall names, address and data in hex:
>> https://gist.githubusercontent.com/dvyukov/19bd59ffa286a74b49ca2371b69d4c5c/raw/004eaaa58a4ca775c008591fbb94eae78f92ef86/gistfile1.txt
>
> add_key(&(0x7f0000d02000)="6465616400", ...
>
> What does the "6465616400" represent? A string containing only numeric
> characters or are these 2-digit hex codes and the string is actually "dead"?

Yes, it is hex. The actual data passed to the syscall is "dead".

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