Re: [RFC][PATCH 2/8] ima: Nest iint mutex for DIGEST_LIST_CHECK hook
From: Roberto Sassu
Date: Fri Mar 08 2024 - 03:01:36 EST
On Thu, 2024-03-07 at 14:42 -0500, Mimi Zohar wrote:
> On Wed, 2024-02-14 at 15:35 +0100, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> >
> > Invoking digest_cache_get() inside the iint->mutex critical region can
> > cause deadlocks due to the fact that IMA can be recursively invoked for
> > reading the digest list. The deadlock would occur if the digest_cache LSM
> > attempts to read the same inode that is already locked by IMA.
> >
> > However, since the digest_cache LSM makes sure that the above situation
> > never happens, as it checks the inodes, it is safe to call
> > digest_cache_get() inside the critical region and nest the iint->mutex
> > when the DIGEST_LIST_CHECK hook is executed.
> >
> > Add a lockdep subclass to the iint->mutex, that is 0 if the IMA hook
> > executed is not DIGEST_LIST_CHECK, and 1 when it is. Since lockdep allows
> > nesting with higher classes and subclasses, that effectively eliminates the
> > warning about the unsafe lock.
> >
> > Pass the new lockdep subclass (nested variable) from ima_inode_get() to
> > ima_iint_init_always() and ima_iint_lockdep_annotate().
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > ---
> > security/integrity/ima/ima.h | 2 +-
> > security/integrity/ima/ima_iint.c | 11 ++++++-----
> > security/integrity/ima/ima_main.c | 6 +++---
> > 3 files changed, 10 insertions(+), 9 deletions(-)
> >
> > diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> > index cea4517e73ab..c9140a57b591 100644
> > --- a/security/integrity/ima/ima.h
> > +++ b/security/integrity/ima/ima.h
> > @@ -216,7 +216,7 @@ static inline void ima_inode_set_iint(const struct inode
> > *inode,
> > }
> >
> > struct ima_iint_cache *ima_iint_find(struct inode *inode);
> > -struct ima_iint_cache *ima_inode_get(struct inode *inode);
> > +struct ima_iint_cache *ima_inode_get(struct inode *inode, bool nested);
> > void ima_inode_free(struct inode *inode);
> > void __init ima_iintcache_init(void);
> >
> > diff --git a/security/integrity/ima/ima_iint.c
> > b/security/integrity/ima/ima_iint.c
> > index e7c9c216c1c6..b4f476fae437 100644
> > --- a/security/integrity/ima/ima_iint.c
> > +++ b/security/integrity/ima/ima_iint.c
> > @@ -41,7 +41,7 @@ struct ima_iint_cache *ima_iint_find(struct inode *inode)
> > * See ovl_lockdep_annotate_inode_mutex_key() for more details.
> > */
> > static inline void ima_iint_lockdep_annotate(struct ima_iint_cache *iint,
> > - struct inode *inode)
> > + struct inode *inode, bool nested)
> > {
> > #ifdef CONFIG_LOCKDEP
> > static struct lock_class_key ima_iint_mutex_key[IMA_MAX_NESTING];
>
>
> "nested" is being pushed all the way down to here, perhaps I'm missing
> something, but I don't see it being used in any of the patches.
Must have gone away during a conflict resolution...
That should have been:
@@ -85,12 +85,13 @@ static inline void iint_lockdep_annotate(struct integrity_iint_cache *iint,
if (WARN_ON_ONCE(depth < 0 || depth >= IMA_MAX_NESTING))
depth = 0;
- lockdep_set_class(&iint->mutex, &iint_mutex_key[depth]);
+ lockdep_set_class_and_subclass(&iint->mutex, &iint_mutex_key[depth],
+ nested);
#endif
}
static void iint_init_always(struct integrity_iint_cache *iint,
- struct inode *inode)
+ struct inode *inode, bool nested)
{
iint->ima_hash = NULL;
iint->version = 0;
Thanks
Roberto
> Mimi
>
> > @@ -56,7 +56,7 @@ static inline void ima_iint_lockdep_annotate(struct
> > ima_iint_cache *iint,
> > }
> >
> > static void ima_iint_init_always(struct ima_iint_cache *iint,
> > - struct inode *inode)
> > + struct inode *inode, bool nested)
> > {
> > iint->ima_hash = NULL;
> > iint->version = 0;
> > @@ -69,7 +69,7 @@ static void ima_iint_init_always(struct ima_iint_cache
> > *iint,
> > iint->ima_creds_status = INTEGRITY_UNKNOWN;
> > iint->measured_pcrs = 0;
> > mutex_init(&iint->mutex);
> > - ima_iint_lockdep_annotate(iint, inode);
> > + ima_iint_lockdep_annotate(iint, inode, nested);
> > }
> >
> > static void ima_iint_free(struct ima_iint_cache *iint)
> > @@ -82,13 +82,14 @@ static void ima_iint_free(struct ima_iint_cache *iint)
> > /**
> > * ima_inode_get - Find or allocate an iint associated with an inode
> > * @inode: Pointer to the inode
> > + * @nested: Whether or not the iint->mutex lock can be nested
> > *
> > * Find an iint associated with an inode, and allocate a new one if not
> > found.
> > * Caller must lock i_mutex.
> > *
> > * Return: An iint on success, NULL on error.
> > */
> > -struct ima_iint_cache *ima_inode_get(struct inode *inode)
> > +struct ima_iint_cache *ima_inode_get(struct inode *inode, bool nested)
> > {
> > struct ima_iint_cache *iint;
> >
> > @@ -100,7 +101,7 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
> > if (!iint)
> > return NULL;
> >
> > - ima_iint_init_always(iint, inode);
> > + ima_iint_init_always(iint, inode, nested);
> >
> > inode->i_flags |= S_IMA;
> > ima_inode_set_iint(inode, iint);
> > diff --git a/security/integrity/ima/ima_main.c
> > b/security/integrity/ima/ima_main.c
> > index 780627b0cde7..18285fc8ac07 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -248,7 +248,7 @@ static int process_measurement(struct file *file, const
> > struct cred *cred,
> > inode_lock(inode);
> >
> > if (action) {
> > - iint = ima_inode_get(inode);
> > + iint = ima_inode_get(inode, func == DIGEST_LIST_CHECK);
> > if (!iint)
> > rc = -ENOMEM;
> > }
> > @@ -699,7 +699,7 @@ static void ima_post_create_tmpfile(struct mnt_idmap
> > *idmap,
> > return;
> >
> > /* Nothing to do if we can't allocate memory */
> > - iint = ima_inode_get(inode);
> > + iint = ima_inode_get(inode, false);
> > if (!iint)
> > return;
> >
> > @@ -731,7 +731,7 @@ static void ima_post_path_mknod(struct mnt_idmap *idmap,
> > struct dentry *dentry)
> > return;
> >
> > /* Nothing to do if we can't allocate memory */
> > - iint = ima_inode_get(inode);
> > + iint = ima_inode_get(inode, false);
> > if (!iint)
> > return;
> >