diff mbox series

integrity: evm: Fix RCU list related warnings.

Message ID 20200430160205.17798-1-madhuparnabhowmik10@gmail.com (mailing list archive)
State New, archived
Headers show
Series integrity: evm: Fix RCU list related warnings. | expand

Commit Message

Madhuparna Bhowmik April 30, 2020, 4:02 p.m. UTC 
From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

This patch fixes the following warning and few other
instances of traversal of evm_config_xattrnames list:

[   32.848432] =============================
[   32.848707] WARNING: suspicious RCU usage
[   32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted
[   32.849308] -----------------------------
[   32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!!

Since entries are only added to the list and never deleted,
use list_For_each_entry_lockless() instead of
list_for_each_entry_rcu() for traversing the list.
Also, add a relevant comment in evm_secfs.c to indicate this fact.

Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 security/integrity/evm/evm_crypto.c | 2 +-
 security/integrity/evm/evm_main.c   | 4 ++--
 security/integrity/evm/evm_secfs.c  | 9 ++++++++-
 3 files changed, 11 insertions(+), 4 deletions(-)

Comments

Paul E. McKenney April 30, 2020, 4:25 p.m. UTC | #1 
On Thu, Apr 30, 2020 at 09:32:05PM +0530, madhuparnabhowmik10@gmail.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> This patch fixes the following warning and few other
> instances of traversal of evm_config_xattrnames list:
> 
> [   32.848432] =============================
> [   32.848707] WARNING: suspicious RCU usage
> [   32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted
> [   32.849308] -----------------------------
> [   32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!!
> 
> Since entries are only added to the list and never deleted,
> use list_For_each_entry_lockless() instead of
> list_for_each_entry_rcu() for traversing the list.
> Also, add a relevant comment in evm_secfs.c to indicate this fact.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

From an RCU viewpoint:

Acked-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  security/integrity/evm/evm_crypto.c | 2 +-
>  security/integrity/evm/evm_main.c   | 4 ++--
>  security/integrity/evm/evm_secfs.c  | 9 ++++++++-
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index 35682852ddea..b2dc87da5f50 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -207,7 +207,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  	data->hdr.length = crypto_shash_digestsize(desc->tfm);
>  
>  	error = -ENODATA;
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		bool is_ima = false;
>  
>  		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index d361d7fdafc4..0d36259b690d 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -97,7 +97,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
>  	if (!(inode->i_opflags & IOP_XATTR))
>  		return -EOPNOTSUPP;
>  
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
>  		if (error < 0) {
>  			if (error == -ENODATA)
> @@ -228,7 +228,7 @@ static int evm_protected_xattr(const char *req_xattr_name)
>  	struct xattr_list *xattr;
>  
>  	namelen = strlen(req_xattr_name);
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		if ((strlen(xattr->name) == namelen)
>  		    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
>  			found = 1;
> diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> index 39ad1038d45d..cfc3075769bb 100644
> --- a/security/integrity/evm/evm_secfs.c
> +++ b/security/integrity/evm/evm_secfs.c
> @@ -232,7 +232,14 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
>  		goto out;
>  	}
>  
> -	/* Guard against races in evm_read_xattrs */
> +	/*
> +	 * xattr_list_mutex guards against races in evm_read_xattrs().
> +	 * Entries are only added to the evm_config_xattrnames list
> +	 * and never deleted. Therefore, the list is traversed
> +	 * using list_for_each_entry_lockless() without holding
> +	 * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
> +	 * and evm_protected_xattr().
> +	 */
>  	mutex_lock(&xattr_list_mutex);
>  	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
>  		if (strcmp(xattr->name, tmp->name) == 0) {
> -- 
> 2.17.1
>
Stephen Rothwell May 8, 2020, 12:14 a.m. UTC | #2 
Hi all,

On Thu, 30 Apr 2020 21:32:05 +0530 madhuparnabhowmik10@gmail.com wrote:
>
> From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> 
> This patch fixes the following warning and few other
> instances of traversal of evm_config_xattrnames list:
> 
> [   32.848432] =============================
> [   32.848707] WARNING: suspicious RCU usage
> [   32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted
> [   32.849308] -----------------------------
> [   32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!!
> 
> Since entries are only added to the list and never deleted,
> use list_For_each_entry_lockless() instead of
> list_for_each_entry_rcu() for traversing the list.
> Also, add a relevant comment in evm_secfs.c to indicate this fact.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> Acked-by: Paul E. McKenney <paulmck@kernel.org>
> ---
>  security/integrity/evm/evm_crypto.c | 2 +-
>  security/integrity/evm/evm_main.c   | 4 ++--
>  security/integrity/evm/evm_secfs.c  | 9 ++++++++-
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index 35682852ddea..b2dc87da5f50 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -207,7 +207,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  	data->hdr.length = crypto_shash_digestsize(desc->tfm);
>  
>  	error = -ENODATA;
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		bool is_ima = false;
>  
>  		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index d361d7fdafc4..0d36259b690d 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -97,7 +97,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
>  	if (!(inode->i_opflags & IOP_XATTR))
>  		return -EOPNOTSUPP;
>  
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
>  		if (error < 0) {
>  			if (error == -ENODATA)
> @@ -228,7 +228,7 @@ static int evm_protected_xattr(const char *req_xattr_name)
>  	struct xattr_list *xattr;
>  
>  	namelen = strlen(req_xattr_name);
> -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
>  		if ((strlen(xattr->name) == namelen)
>  		    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
>  			found = 1;
> diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> index 39ad1038d45d..cfc3075769bb 100644
> --- a/security/integrity/evm/evm_secfs.c
> +++ b/security/integrity/evm/evm_secfs.c
> @@ -232,7 +232,14 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
>  		goto out;
>  	}
>  
> -	/* Guard against races in evm_read_xattrs */
> +	/*
> +	 * xattr_list_mutex guards against races in evm_read_xattrs().
> +	 * Entries are only added to the evm_config_xattrnames list
> +	 * and never deleted. Therefore, the list is traversed
> +	 * using list_for_each_entry_lockless() without holding
> +	 * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
> +	 * and evm_protected_xattr().
> +	 */
>  	mutex_lock(&xattr_list_mutex);
>  	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
>  		if (strcmp(xattr->name, tmp->name) == 0) {

I will apply this to linux-next today.

Is there something stopping this being applied to a tree?  And does it
need to be sent to Linus soon?
Mimi Zohar May 8, 2020, 12:23 a.m. UTC | #3 
Hi Stephen,

On Fri, 2020-05-08 at 10:14 +1000, Stephen Rothwell wrote:
> Hi all,
> 
> On Thu, 30 Apr 2020 21:32:05 +0530 madhuparnabhowmik10@gmail.com wrote:
> >
> > From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > 
> > This patch fixes the following warning and few other
> > instances of traversal of evm_config_xattrnames list:
> > 
> > [   32.848432] =============================
> > [   32.848707] WARNING: suspicious RCU usage
> > [   32.848966] 5.7.0-rc1-00006-ga8d5875ce5f0b #1 Not tainted
> > [   32.849308] -----------------------------
> > [   32.849567] security/integrity/evm/evm_main.c:231 RCU-list traversed in non-reader section!!
> > 
> > Since entries are only added to the list and never deleted,
> > use list_For_each_entry_lockless() instead of
> > list_for_each_entry_rcu() for traversing the list.
> > Also, add a relevant comment in evm_secfs.c to indicate this fact.
> > 
> > Reported-by: kernel test robot <lkp@intel.com>
> > Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
> > Acked-by: Paul E. McKenney <paulmck@kernel.org>
> > ---
> >  security/integrity/evm/evm_crypto.c | 2 +-
> >  security/integrity/evm/evm_main.c   | 4 ++--
> >  security/integrity/evm/evm_secfs.c  | 9 ++++++++-
> >  3 files changed, 11 insertions(+), 4 deletions(-)
> > 
> > diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> > index 35682852ddea..b2dc87da5f50 100644
> > --- a/security/integrity/evm/evm_crypto.c
> > +++ b/security/integrity/evm/evm_crypto.c
> > @@ -207,7 +207,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
> >  	data->hdr.length = crypto_shash_digestsize(desc->tfm);
> >  
> >  	error = -ENODATA;
> > -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> > +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
> >  		bool is_ima = false;
> >  
> >  		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
> > diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> > index d361d7fdafc4..0d36259b690d 100644
> > --- a/security/integrity/evm/evm_main.c
> > +++ b/security/integrity/evm/evm_main.c
> > @@ -97,7 +97,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
> >  	if (!(inode->i_opflags & IOP_XATTR))
> >  		return -EOPNOTSUPP;
> >  
> > -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> > +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
> >  		error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
> >  		if (error < 0) {
> >  			if (error == -ENODATA)
> > @@ -228,7 +228,7 @@ static int evm_protected_xattr(const char *req_xattr_name)
> >  	struct xattr_list *xattr;
> >  
> >  	namelen = strlen(req_xattr_name);
> > -	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
> > +	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
> >  		if ((strlen(xattr->name) == namelen)
> >  		    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
> >  			found = 1;
> > diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> > index 39ad1038d45d..cfc3075769bb 100644
> > --- a/security/integrity/evm/evm_secfs.c
> > +++ b/security/integrity/evm/evm_secfs.c
> > @@ -232,7 +232,14 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
> >  		goto out;
> >  	}
> >  
> > -	/* Guard against races in evm_read_xattrs */
> > +	/*
> > +	 * xattr_list_mutex guards against races in evm_read_xattrs().
> > +	 * Entries are only added to the evm_config_xattrnames list
> > +	 * and never deleted. Therefore, the list is traversed
> > +	 * using list_for_each_entry_lockless() without holding
> > +	 * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
> > +	 * and evm_protected_xattr().
> > +	 */
> >  	mutex_lock(&xattr_list_mutex);
> >  	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
> >  		if (strcmp(xattr->name, tmp->name) == 0) {
> 
> I will apply this to linux-next today.
> 
> Is there something stopping this being applied to a tree?  And does it
> need to be sent to Linus soon?

Sorry for the delay in pushing this and other fixes to the next-
integrity branch.  It's in my next-integrity-testing branch.

This isn't a bug per-se, just annotating the reason for the lack of
locking.

thanks,

Mimi
Stephen Rothwell May 8, 2020, 1:21 a.m. UTC | #4 
Hi Mimi,

On Thu, 07 May 2020 20:23:41 -0400 Mimi Zohar <zohar@linux.ibm.com> wrote:
>
> Sorry for the delay in pushing this and other fixes to the next-
> integrity branch.  It's in my next-integrity-testing branch.

OK, thanks.

> This isn't a bug per-se, just annotating the reason for the lack of
> locking.

Yes, but these warnings stop the syzbot's testing in its tracks :-(
diff mbox series

Patch

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 35682852ddea..b2dc87da5f50 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -207,7 +207,7 @@  static int evm_calc_hmac_or_hash(struct dentry *dentry,
 	data->hdr.length = crypto_shash_digestsize(desc->tfm);
 
 	error = -ENODATA;
-	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
+	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 		bool is_ima = false;
 
 		if (strcmp(xattr->name, XATTR_NAME_IMA) == 0)
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index d361d7fdafc4..0d36259b690d 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -97,7 +97,7 @@  static int evm_find_protected_xattrs(struct dentry *dentry)
 	if (!(inode->i_opflags & IOP_XATTR))
 		return -EOPNOTSUPP;
 
-	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
+	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 		error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
 		if (error < 0) {
 			if (error == -ENODATA)
@@ -228,7 +228,7 @@  static int evm_protected_xattr(const char *req_xattr_name)
 	struct xattr_list *xattr;
 
 	namelen = strlen(req_xattr_name);
-	list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) {
+	list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
 		if ((strlen(xattr->name) == namelen)
 		    && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
 			found = 1;
diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index 39ad1038d45d..cfc3075769bb 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c
@@ -232,7 +232,14 @@  static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 		goto out;
 	}
 
-	/* Guard against races in evm_read_xattrs */
+	/*
+	 * xattr_list_mutex guards against races in evm_read_xattrs().
+	 * Entries are only added to the evm_config_xattrnames list
+	 * and never deleted. Therefore, the list is traversed
+	 * using list_for_each_entry_lockless() without holding
+	 * the mutex in evm_calc_hmac_or_hash(), evm_find_protected_xattrs()
+	 * and evm_protected_xattr().
+	 */
 	mutex_lock(&xattr_list_mutex);
 	list_for_each_entry(tmp, &evm_config_xattrnames, list) {
 		if (strcmp(xattr->name, tmp->name) == 0) {