[PATCH 02/11] UBUNTU: SAUCE: apparmor: fix replacement race in reading rawdata

John Johansen john.johansen at canonical.com
Fri Mar 31 12:57:35 UTC 2017

The reading of rawdata is subject to a replacement race when the
rawdata is read in chunks smaller than the data size.

For each read the profile proxy is rechecked for the newest profile;
Which means if a profile is replaced between reads later chunks will
contain data from the new version of the profile while the earlier
reads will contain data from the previous version. This can result in
data that is inconsistent and corrupt.

Instead of rechecking for the current profile at each read. Get the
current profile at the time of the open and use the rawdata of the
profile for the lifetime that the file handle is open.

BugLink: http://bugs.launchpad.net/bugs/1638996
Signed-off-by: John Johansen <john.johansen at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
Acked-by: Tim Gardner <tim.gardner at canonical.com>
Acked-by: Brad Figg <brad.figg at canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
 security/apparmor/apparmorfs.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 28c95b3..b8ba1bb 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -766,7 +766,7 @@ static const struct file_operations aa_fs_ns_name = {
 static int rawdata_release(struct inode *inode, struct file *file)
 	/* TODO: switch to loaddata when profile switched to symlink */
-	aa_put_proxy(file->private_data);
+	aa_put_loaddata(file->private_data);
 	return 0;
@@ -832,22 +832,24 @@ static const struct file_operations aa_fs_seq_raw_hash_fops = {
 static ssize_t rawdata_read(struct file *file, char __user *buf, size_t size,
 			    loff_t *ppos)
-	struct aa_proxy *proxy = file->private_data;
-	struct aa_label *label = aa_get_label_rcu(&proxy->label);
-	struct aa_profile *profile = labels_profile(label);
+	struct aa_loaddata *rawdata = file->private_data;
-	ssize_t ret = simple_read_from_buffer(buf, size, ppos, profile->rawdata->data, profile->rawdata->size);
-	aa_put_label(label);
-	return ret;
+	return simple_read_from_buffer(buf, size, ppos, rawdata->data,
+				       rawdata->size);
 static int rawdata_open(struct inode *inode, struct file *file)
+	struct aa_proxy *proxy = inode->i_private;
+	struct aa_label *label;
+	struct aa_profile *profile;
 	if (!policy_view_capable(NULL))
 		return -EACCES;
-	file->private_data = aa_get_proxy(inode->i_private);
+	label = aa_get_label_rcu(&proxy->label);
+	profile = labels_profile(label);
+	file->private_data = aa_get_loaddata(profile->rawdata);
+	aa_put_label(label);
 	return 0;

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