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Subject[PATCH 4.17 215/220] selinux: move user accesses in selinuxfs out of locked regions
Date
4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@google.com>

commit 0da74120c5341389b97c4ee27487a97224999ee1 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/selinux/selinuxfs.c | 78 ++++++++++++++++++-------------------------
1 file changed, 33 insertions(+), 45 deletions(-)

--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -435,22 +435,16 @@ static int sel_release_policy(struct ino
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 int sel_mmap_policy_fault(struct vm_fault *vmf)
@@ -1182,25 +1176,29 @@ static ssize_t sel_read_bool(struct file
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,
@@ -1213,6 +1211,17 @@ static ssize_t sel_write_bool(struct fil
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,
@@ -1227,22 +1236,6 @@ static ssize_t sel_write_bool(struct fil
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;
@@ -1274,6 +1267,17 @@ static ssize_t sel_commit_bools_write(st
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,
@@ -1283,22 +1287,6 @@ static ssize_t sel_commit_bools_write(st
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;

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