The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 0da74120c5341389b97c4ee27487a97224999ee1 Mon Sep 17 00:00:00 2001

From: Jann Horn jannh@google.com Date: Thu, 28 Jun 2018 20:39:54 -0400 Subject: [PATCH] selinux: move user accesses in selinuxfs out of locked regions

If a user is accessing a file in selinuxfs with a pointer to a userspace buffer that is backed by e.g. a userfaultfd, the userspace access can stall indefinitely, which can block fsi->mutex if it is held.

For sel_read_policy(), remove the locking, since this method doesn't seem to access anything that requires locking.

For sel_read_bool(), move the user access below the locked region.

For sel_write_bool() and sel_commit_bools_write(), move the user access up above the locked region.

Cc: stable@vger.kernel.org Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Jann Horn jannh@google.com Acked-by: Stephen Smalley sds@tycho.nsa.gov [PM: removed an unused variable in sel_read_policy()] Signed-off-by: Paul Moore paul@paul-moore.com

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c index c0cadbc5f85c..19e35dd695d7 100644 --- a/security/selinux/selinuxfs.c +++ b/security/selinux/selinuxfs.c @@ -441,22 +441,16 @@ static int sel_release_policy(struct inode *inode, struct file *filp) static ssize_t sel_read_policy(struct file *filp, char __user *buf, size_t count, loff_t *ppos) { - struct selinux_fs_info *fsi = file_inode(filp)->i_sb->s_fs_info; struct policy_load_memory *plm = filp->private_data; int ret;

- mutex_lock(&fsi->mutex); - ret = avc_has_perm(&selinux_state, current_sid(), SECINITSID_SECURITY, SECCLASS_SECURITY, SECURITY__READ_POLICY, NULL); if (ret) - goto out; + return ret;

- ret = simple_read_from_buffer(buf, count, ppos, plm->data, plm->len); -out: - mutex_unlock(&fsi->mutex); - return ret; + return simple_read_from_buffer(buf, count, ppos, plm->data, plm->len); }

static vm_fault_t sel_mmap_policy_fault(struct vm_fault *vmf) @@ -1188,25 +1182,29 @@ static ssize_t sel_read_bool(struct file *filep, char __user *buf, ret = -EINVAL; if (index >= fsi->bool_num || strcmp(name, fsi->bool_pending_names[index])) - goto out; + goto out_unlock;

ret = -ENOMEM; page = (char *)get_zeroed_page(GFP_KERNEL); if (!page) - goto out; + goto out_unlock;

cur_enforcing = security_get_bool_value(fsi->state, index); if (cur_enforcing < 0) { ret = cur_enforcing; - goto out; + goto out_unlock; } length = scnprintf(page, PAGE_SIZE, "%d %d", cur_enforcing, fsi->bool_pending_values[index]); - ret = simple_read_from_buffer(buf, count, ppos, page, length); -out: mutex_unlock(&fsi->mutex); + ret = simple_read_from_buffer(buf, count, ppos, page, length); +out_free: free_page((unsigned long)page); return ret; + +out_unlock: + mutex_unlock(&fsi->mutex); + goto out_free; }

static ssize_t sel_write_bool(struct file *filep, const char __user *buf, @@ -1219,6 +1217,17 @@ static ssize_t sel_write_bool(struct file *filep, const char __user *buf, unsigned index = file_inode(filep)->i_ino & SEL_INO_MASK; const char *name = filep->f_path.dentry->d_name.name;

+ if (count >= PAGE_SIZE) + return -ENOMEM; + + /* No partial writes. */ + if (*ppos != 0) + return -EINVAL; + + page = memdup_user_nul(buf, count); + if (IS_ERR(page)) + return PTR_ERR(page); + mutex_lock(&fsi->mutex);

length = avc_has_perm(&selinux_state, @@ -1233,22 +1242,6 @@ static ssize_t sel_write_bool(struct file *filep, const char __user *buf, fsi->bool_pending_names[index])) goto out;

- length = -ENOMEM; - if (count >= PAGE_SIZE) - goto out; - - /* No partial writes. */ - length = -EINVAL; - if (*ppos != 0) - goto out; - - page = memdup_user_nul(buf, count); - if (IS_ERR(page)) { - length = PTR_ERR(page); - page = NULL; - goto out; - } - length = -EINVAL; if (sscanf(page, "%d", &new_value) != 1) goto out; @@ -1280,6 +1273,17 @@ static ssize_t sel_commit_bools_write(struct file *filep, ssize_t length; int new_value;

+ if (count >= PAGE_SIZE) + return -ENOMEM; + + /* No partial writes. */ + if (*ppos != 0) + return -EINVAL; + + page = memdup_user_nul(buf, count); + if (IS_ERR(page)) + return PTR_ERR(page); + mutex_lock(&fsi->mutex);

length = avc_has_perm(&selinux_state, @@ -1289,22 +1293,6 @@ static ssize_t sel_commit_bools_write(struct file *filep, if (length) goto out;

- length = -ENOMEM; - if (count >= PAGE_SIZE) - goto out; - - /* No partial writes. */ - length = -EINVAL; - if (*ppos != 0) - goto out; - - page = memdup_user_nul(buf, count); - if (IS_ERR(page)) { - length = PTR_ERR(page); - page = NULL; - goto out; - } - length = -EINVAL; if (sscanf(page, "%d", &new_value) != 1) goto out;