selinux: Convert isec->lock into a spinlock

Convert isec->lock from a mutex into a spinlock.  Instead of holding
the lock while sleeping in inode_doinit_with_dentry, set
isec->initialized to LABEL_PENDING and release the lock.  Then, when
the sid has been determined, re-acquire the lock.  If isec->initialized
is still set to LABEL_PENDING, set isec->sid; otherwise, the sid has
been set by another task (LABEL_INITIALIZED) or invalidated
(LABEL_INVALID) in the meantime.

This fixes a deadlock on gfs2 where

 * one task is in inode_doinit_with_dentry -> gfs2_getxattr, holds
   isec->lock, and tries to acquire the inode's glock, and

 * another task is in do_xmote -> inode_go_inval ->
   selinux_inode_invalidate_secctx, holds the inode's glock, and
   tries to acquire isec->lock.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
[PM: minor tweaks to keep checkpatch.pl happy]
Signed-off-by: Paul Moore <paul@paul-moore.com>

2 files changed, 66 insertions, 40 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 2a506861a772..98a2e92b3168 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -231,7 +231,7 @@ static int inode_alloc_security(struct inode *inode)
         if (!isec)
                 return -ENOMEM;
 
-        mutex_init(&isec->lock);
+        spin_lock_init(&isec->lock);
         INIT_LIST_HEAD(&isec->list);
         isec->inode = inode;
         isec->sid = SECINITSID_UNLABELED;
@@ -1382,7 +1382,8 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
 {
         struct superblock_security_struct *sbsec = NULL;
         struct inode_security_struct *isec = inode->i_security;
-        u32 sid;
+        u32 task_sid, sid = 0;
+        u16 sclass;
         struct dentry *dentry;
 #define INITCONTEXTLEN 255
         char *context = NULL;
@@ -1392,7 +1393,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
         if (isec->initialized == LABEL_INITIALIZED)
                 return 0;
 
-        mutex_lock(&isec->lock);
+        spin_lock(&isec->lock);
         if (isec->initialized == LABEL_INITIALIZED)
                 goto out_unlock;
 
@@ -1411,12 +1412,18 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                 goto out_unlock;
         }
 
+        sclass = isec->sclass;
+        task_sid = isec->task_sid;
+        sid = isec->sid;
+        isec->initialized = LABEL_PENDING;
+        spin_unlock(&isec->lock);
+
         switch (sbsec->behavior) {
         case SECURITY_FS_USE_NATIVE:
                 break;
         case SECURITY_FS_USE_XATTR:
                 if (!(inode->i_opflags & IOP_XATTR)) {
-                        isec->sid = sbsec->def_sid;
+                        sid = sbsec->def_sid;
                         break;
                 }
                 /* Need a dentry, since the xattr API requires one.
@@ -1438,7 +1445,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                          * inode_doinit with a dentry, before these inodes could
                          * be used again by userspace.
                          */
-                        goto out_unlock;
+                        goto out;
                 }
 
                 len = INITCONTEXTLEN;
@@ -1446,7 +1453,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                 if (!context) {
                         rc = -ENOMEM;
                         dput(dentry);
-                        goto out_unlock;
+                        goto out;
                 }
                 context[len] = '\0';
                 rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
@@ -1457,14 +1464,14 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                         rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, NULL, 0);
                         if (rc < 0) {
                                 dput(dentry);
-                                goto out_unlock;
+                                goto out;
                         }
                         len = rc;
                         context = kmalloc(len+1, GFP_NOFS);
                         if (!context) {
                                 rc = -ENOMEM;
                                 dput(dentry);
-                                goto out_unlock;
+                                goto out;
                         }
                         context[len] = '\0';
                         rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
@@ -1476,7 +1483,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                                        "%d for dev=%s ino=%ld\n", __func__,
                                        -rc, inode->i_sb->s_id, inode->i_ino);
                                 kfree(context);
-                                goto out_unlock;
+                                goto out;
                         }
                         /* Map ENODATA to the default file SID */
                         sid = sbsec->def_sid;
@@ -1506,28 +1513,25 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                         }
                 }
                 kfree(context);
-                isec->sid = sid;
                 break;
         case SECURITY_FS_USE_TASK:
-                isec->sid = isec->task_sid;
+                sid = task_sid;
                 break;
         case SECURITY_FS_USE_TRANS:
                 /* Default to the fs SID. */
-                isec->sid = sbsec->sid;
+                sid = sbsec->sid;
 
                 /* Try to obtain a transition SID. */
-                rc = security_transition_sid(isec->task_sid, sbsec->sid,
-                                             isec->sclass, NULL, &sid);
+                rc = security_transition_sid(task_sid, sid, sclass, NULL, &sid);
                 if (rc)
-                        goto out_unlock;
-                isec->sid = sid;
+                        goto out;
                 break;
         case SECURITY_FS_USE_MNTPOINT:
-                isec->sid = sbsec->mntpoint_sid;
+                sid = sbsec->mntpoint_sid;
                 break;
         default:
                 /* Default to the fs superblock SID. */
-                isec->sid = sbsec->sid;
+                sid = sbsec->sid;
 
                 if ((sbsec->flags & SE_SBGENFS) && !S_ISLNK(inode->i_mode)) {
                         /* We must have a dentry to determine the label on
@@ -1550,21 +1554,30 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                          * could be used again by userspace.
                          */
                         if (!dentry)
-                                goto out_unlock;
-                        rc = selinux_genfs_get_sid(dentry, isec->sclass,
+                                goto out;
+                        rc = selinux_genfs_get_sid(dentry, sclass,
                                                    sbsec->flags, &sid);
                         dput(dentry);
                         if (rc)
-                                goto out_unlock;
-                        isec->sid = sid;
+                                goto out;
                 }
                 break;
         }
 
-        isec->initialized = LABEL_INITIALIZED;
+out:
+        spin_lock(&isec->lock);
+        if (isec->initialized == LABEL_PENDING) {
+                if (!sid || rc) {
+                        isec->initialized = LABEL_INVALID;
+                        goto out_unlock;
+                }
+
+                isec->initialized = LABEL_INITIALIZED;
+                isec->sid = sid;
+        }
 
 out_unlock:
-        mutex_unlock(&isec->lock);
+        spin_unlock(&isec->lock);
         return rc;
 }
 
@@ -3195,9 +3208,11 @@ static void selinux_inode_post_setxattr(struct dentry *dentry, const char *name,
         }
 
         isec = backing_inode_security(dentry);
+        spin_lock(&isec->lock);
         isec->sclass = inode_mode_to_security_class(inode->i_mode);
         isec->sid = newsid;
         isec->initialized = LABEL_INITIALIZED;
+        spin_unlock(&isec->lock);
 
         return;
 }
@@ -3290,9 +3305,11 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name,
         if (rc)
                 return rc;
 
+        spin_lock(&isec->lock);
         isec->sclass = inode_mode_to_security_class(inode->i_mode);
         isec->sid = newsid;
         isec->initialized = LABEL_INITIALIZED;
+        spin_unlock(&isec->lock);
         return 0;
 }
 
@@ -3953,9 +3970,11 @@ static void selinux_task_to_inode(struct task_struct *p,
         struct inode_security_struct *isec = inode->i_security;
         u32 sid = task_sid(p);
 
+        spin_lock(&isec->lock);
         isec->sclass = inode_mode_to_security_class(inode->i_mode);
         isec->sid = sid;
         isec->initialized = LABEL_INITIALIZED;
+        spin_unlock(&isec->lock);
 }
 
 /* Returns error only if unable to parse addresses */
@@ -4274,24 +4293,24 @@ static int selinux_socket_post_create(struct socket *sock, int family,
         const struct task_security_struct *tsec = current_security();
         struct inode_security_struct *isec = inode_security_novalidate(SOCK_INODE(sock));
         struct sk_security_struct *sksec;
+        u16 sclass = socket_type_to_security_class(family, type, protocol);
+        u32 sid = SECINITSID_KERNEL;
         int err = 0;
 
-        isec->sclass = socket_type_to_security_class(family, type, protocol);
-
-        if (kern)
-                isec->sid = SECINITSID_KERNEL;
-        else {
-                err = socket_sockcreate_sid(tsec, isec->sclass, &(isec->sid));
+        if (!kern) {
+                err = socket_sockcreate_sid(tsec, sclass, &sid);
                 if (err)
                         return err;
         }
 
+        isec->sclass = sclass;
+        isec->sid = sid;
         isec->initialized = LABEL_INITIALIZED;
 
         if (sock->sk) {
                 sksec = sock->sk->sk_security;
-                sksec->sid = isec->sid;
-                sksec->sclass = isec->sclass;
+                sksec->sclass = sclass;
+                sksec->sid = sid;
                 err = selinux_netlbl_socket_post_create(sock->sk, family);
         }
 
@@ -4467,16 +4486,22 @@ static int selinux_socket_accept(struct socket *sock, struct socket *newsock)
         int err;
         struct inode_security_struct *isec;
         struct inode_security_struct *newisec;
+        u16 sclass;
+        u32 sid;
 
         err = sock_has_perm(current, sock->sk, SOCKET__ACCEPT);
         if (err)
                 return err;
 
-        newisec = inode_security_novalidate(SOCK_INODE(newsock));
-
         isec = inode_security_novalidate(SOCK_INODE(sock));
-        newisec->sclass = isec->sclass;
-        newisec->sid = isec->sid;
+        spin_lock(&isec->lock);
+        sclass = isec->sclass;
+        sid = isec->sid;
+        spin_unlock(&isec->lock);
+
+        newisec = inode_security_novalidate(SOCK_INODE(newsock));
+        newisec->sclass = sclass;
+        newisec->sid = sid;
         newisec->initialized = LABEL_INITIALIZED;
 
         return 0;
@@ -5979,9 +6004,9 @@ static void selinux_inode_invalidate_secctx(struct inode *inode)
 {
         struct inode_security_struct *isec = inode->i_security;
 
-        mutex_lock(&isec->lock);
+        spin_lock(&isec->lock);
         isec->initialized = LABEL_INVALID;
-        mutex_unlock(&isec->lock);
+        spin_unlock(&isec->lock);
 }
 
 /*
diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
index c21e135460a5..e8dab0f02c72 100644
--- a/security/selinux/include/objsec.h
+++ b/security/selinux/include/objsec.h
@@ -39,7 +39,8 @@ struct task_security_struct {
 
 enum label_initialized {
         LABEL_INVALID,          /* invalid or not initialized */
-        LABEL_INITIALIZED       /* initialized */
+        LABEL_INITIALIZED,      /* initialized */
+        LABEL_PENDING
 };
 
 struct inode_security_struct {
@@ -52,7 +53,7 @@ struct inode_security_struct {
         u32 sid;                /* SID of this object */
         u16 sclass;             /* security class of this object */
         unsigned char initialized;      /* initialization flag */
-        struct mutex lock;
+        spinlock_t lock;
 };
 
 struct file_security_struct {