linux-kernel - Re: [PATCH v2] KEYS: always initialize keyring_index_key::desc

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Date:   Tue, 19 Feb 2019 15:04:35 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     James Morris <jmorris@...ei.org>
Cc:     keyrings@...r.kernel.org, David Howells <dhowells@...hat.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v2] KEYS: always initialize keyring_index_key::desc_len

On Thu, Feb 07, 2019 at 03:35:29PM -0800, Eric Biggers wrote:
> On Thu, Jan 10, 2019 at 12:27:46PM -0800, Eric Biggers wrote:
> > On Wed, Nov 28, 2018 at 03:19:41PM -0800, Eric Biggers wrote:
> > > On Fri, Nov 02, 2018 at 06:58:54PM -0700, Eric Biggers wrote:
> > > > From: Eric Biggers <ebiggers@...gle.com>
> > > > 
> > > > syzbot hit the 'BUG_ON(index_key->desc_len == 0);' in __key_link_begin()
> > > > called from construct_alloc_key() during sys_request_key(), because the
> > > > length of the key description was never calculated.
> > > > 
> > > > The problem is that we rely on ->desc_len being initialized by
> > > > search_process_keyrings(), specifically by search_nested_keyrings().
> > > > But, if the process isn't subscribed to any keyrings that never happens.
> > > > 
> > > > Fix it by always initializing keyring_index_key::desc_len as soon as the
> > > > description is set, like we already do in some places.
> > > > 
> > > > The following program reproduces the BUG_ON() when it's run as root and
> > > > no session keyring has been installed.  If it doesn't work, try removing
> > > > pam_keyinit.so from /etc/pam.d/login and rebooting.
> > > > 
> > > >     #include <stdlib.h>
> > > >     #include <unistd.h>
> > > >     #include <keyutils.h>
> > > > 
> > > >     int main(void)
> > > >     {
> > > >             int id = add_key("keyring", "syz", NULL, 0, KEY_SPEC_USER_KEYRING);
> > > > 
> > > >             keyctl_setperm(id, KEY_OTH_WRITE);
> > > >             setreuid(5000, 5000);
> > > >             request_key("user", "desc", "", id);
> > > >     }
> > > > 
> > > > Reported-by: syzbot+ec24e95ea483de0a24da@...kaller.appspotmail.com
> > > > Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
> > > > Cc: <stable@...r.kernel.org> # v3.13+
> > > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > > ---
> > > > 
> > > > v2: In proc_keys_show(), assign index_key directly
> > > > 
> > > >  security/keys/keyring.c          | 4 +---
> > > >  security/keys/proc.c             | 3 +--
> > > >  security/keys/request_key.c      | 1 +
> > > >  security/keys/request_key_auth.c | 2 +-
> > > >  4 files changed, 4 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> > > > index 41bcf57e96f21..99a55145ddcd2 100644
> > > > --- a/security/keys/keyring.c
> > > > +++ b/security/keys/keyring.c
> > > > @@ -661,9 +661,6 @@ static bool search_nested_keyrings(struct key *keyring,
> > > >  	BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
> > > >  	       (ctx->flags & STATE_CHECKS) == STATE_CHECKS);
> > > >  
> > > > -	if (ctx->index_key.description)
> > > > -		ctx->index_key.desc_len = strlen(ctx->index_key.description);
> > > > -
> > > >  	/* Check to see if this top-level keyring is what we are looking for
> > > >  	 * and whether it is valid or not.
> > > >  	 */
> > > > @@ -914,6 +911,7 @@ key_ref_t keyring_search(key_ref_t keyring,
> > > >  	struct keyring_search_context ctx = {
> > > >  		.index_key.type		= type,
> > > >  		.index_key.description	= description,
> > > > +		.index_key.desc_len	= strlen(description),
> > > >  		.cred			= current_cred(),
> > > >  		.match_data.cmp		= key_default_cmp,
> > > >  		.match_data.raw_data	= description,
> > > > diff --git a/security/keys/proc.c b/security/keys/proc.c
> > > > index 5af2934965d80..d38be9db2cc07 100644
> > > > --- a/security/keys/proc.c
> > > > +++ b/security/keys/proc.c
> > > > @@ -166,8 +166,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
> > > >  	int rc;
> > > >  
> > > >  	struct keyring_search_context ctx = {
> > > > -		.index_key.type		= key->type,
> > > > -		.index_key.description	= key->description,
> > > > +		.index_key		= key->index_key,
> > > >  		.cred			= m->file->f_cred,
> > > >  		.match_data.cmp		= lookup_user_key_possessed,
> > > >  		.match_data.raw_data	= key,
> > > > diff --git a/security/keys/request_key.c b/security/keys/request_key.c
> > > > index 114f7408feee6..7385536986497 100644
> > > > --- a/security/keys/request_key.c
> > > > +++ b/security/keys/request_key.c
> > > > @@ -545,6 +545,7 @@ struct key *request_key_and_link(struct key_type *type,
> > > >  	struct keyring_search_context ctx = {
> > > >  		.index_key.type		= type,
> > > >  		.index_key.description	= description,
> > > > +		.index_key.desc_len	= strlen(description),
> > > >  		.cred			= current_cred(),
> > > >  		.match_data.cmp		= key_default_cmp,
> > > >  		.match_data.raw_data	= description,
> > > > diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
> > > > index 424e1d90412ea..6797843154f03 100644
> > > > --- a/security/keys/request_key_auth.c
> > > > +++ b/security/keys/request_key_auth.c
> > > > @@ -246,7 +246,7 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id)
> > > >  	struct key *authkey;
> > > >  	key_ref_t authkey_ref;
> > > >  
> > > > -	sprintf(description, "%x", target_id);
> > > > +	ctx.index_key.desc_len = sprintf(description, "%x", target_id);
> > > >  
> > > >  	authkey_ref = search_process_keyrings(&ctx);
> > > >  
> > > > -- 
> > > > 2.19.1
> > > > 
> > > 
> > > Ping.  David, are you planning to apply this?
> > > 
> > > - Eric
> > > 
> > > -- 
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> > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/20181128231940.GB131170%40gmail.com.
> > > For more options, visit https://groups.google.com/d/optout.
> > 
> > Ping.
> > 
> 
> Ping.  David, are you planning to apply this?
> 
> - Eric

Hi James, can you please apply this for v5.1?  This has been ignored by David
for over 3 months with repeated pings.

- Eric