overlayfs: Do not lose security.capability xattr over metadata file copy-up

From a user's point of view, this is just a file copy-up and that should

If a file has been copied up metadata only, and later data is copied up, upper loses any security.capability xattr it has (underlying filesystem clears it as upon file write).

From a user's point of view, this is just a file copy-up and that should not result in losing security.capability xattr. Hence, before data copy up, save security.capability xattr (if any) and restore it on upper after data copy up is complete.

Signed-off-by Vivek Goyal <[email protected]>

---
 fs/overlayfs/copy_up.c   |   24 ++++++++++++++++++-
 fs/overlayfs/overlayfs.h |    1
 fs/overlayfs/util.c      |   58 +++++++++++++++++++++++++++++++++--------------
 3 files changed, 65 insertions(+), 18 deletions(-)

Index: rhvgoyal-linux/fs/overlayfs/util.c
===================================================================

fs/overlayfs/util.c 2019-01-30 13:48:50.433840084 -0500 renamed from fs/overlayfs/util.c 2019-01-30 13:44:46.123840084 -0500 +41 -17

@@ -863,31 +863,61 @@ bool ovl_is_metacopy_dentry(struct dentr
        return (oe->numlower > 1);
 }
 
-char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+size_t ovl_getxattr(struct dentry *dentry, char *name, void **value,
+                               size_t *size, int padding)
 {
        int res;
-       char *s, *next, *buf = NULL;
+       void *buf = NULL;
 
-       res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
+       res = vfs_getxattr(dentry, name, NULL, 0);
        if (res < 0) {
                if (res == -ENODATA || res == -EOPNOTSUPP)
-                       return NULL;
+                       return 0;
                goto fail;
        }
 
-       buf = kzalloc(res + padding + 1, GFP_KERNEL);
-       if (!buf)
-               return ERR_PTR(-ENOMEM);
-
        if (res == 0)
                goto invalid;
 
-       res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
+       buf = kzalloc(res + padding, GFP_KERNEL);
+       if (!buf)
+               return -ENOMEM;
+
+       res = vfs_getxattr(dentry, name, buf, res);
        if (res < 0)
                goto fail;
+
        if (res == 0)
                goto invalid;
 
+       *value = buf;
+       if (size)
+               *size = res;
+
+       return res;
+
+err_free:
+       kfree(buf);
+       return res;
+fail:
+       pr_warn_ratelimited("overlayfs: failed to get xattr %s: err=%i)\n", name, res);
+       goto err_free;
+invalid:
+       pr_warn_ratelimited("overlayfs: invalid xattr %s \n", name);
+       res = -EINVAL;
+       goto err_free;
+}
+
+char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+{
+       int res;
+       char *s, *next, *buf = NULL;
+
+       res = ovl_getxattr(dentry, OVL_XATTR_REDIRECT, (void **)&buf, NULL,
+               padding + 1);
+       if (res <= 0)
+               return ERR_PTR(res);
+
        if (buf[0] == '/') {
                for (s = buf; *s++ == '/'; s = next) {
                        next = strchrnul(s, '/');

@@ -900,15 +930,9 @@ char *ovl_get_redirect_xattr(struct dent
        }
 
        return buf;
-
-err_free:
-       kfree(buf);
-       return ERR_PTR(res);
-fail:
-       pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
-       goto err_free;
 invalid:
        pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
        res = -EINVAL;
-       goto err_free;
+       kfree(buf);
+       return ERR_PTR(res);
 }

Index: rhvgoyal-linux/fs/overlayfs/overlayfs.h
===================================================================

fs/overlayfs/overlayfs.h 2019-01-30 13:44:48.623840084 -0500 renamed from fs/overlayfs/overlayfs.h 2019-01-30 13:44:46.121840084 -0500 +1 -0

@@ -277,6 +277,7 @@ int ovl_lock_rename_workdir(struct dentr
 int ovl_check_metacopy_xattr(struct dentry *dentry);
 bool ovl_is_metacopy_dentry(struct dentry *dentry);
 char *ovl_get_redirect_xattr(struct dentry *dentry, int padding);
+size_t ovl_getxattr(struct dentry *dentry, char *name, void **value, size_t *size, int padding);
 
 static inline bool ovl_is_impuredir(struct dentry *dentry)
 {

Index: rhvgoyal-linux/fs/overlayfs/copy_up.c
===================================================================

fs/overlayfs/copy_up.c 2019-01-30 13:44:48.624840084 -0500 renamed from fs/overlayfs/copy_up.c 2019-01-30 13:44:46.119840084 -0500 +23 -1

@@ -742,6 +742,8 @@ static int ovl_copy_up_meta_inode_data(s
 {
        struct path upperpath, datapath;
        int err;
+       void *capability = NULL;
+       size_t cap_size;
 
        ovl_path_upper(c->dentry, &upperpath);
        if (WARN_ON(upperpath.dentry == NULL))

@@ -751,9 +753,29 @@ static int ovl_copy_up_meta_inode_data(s
        if (WARN_ON(datapath.dentry == NULL))
                return -EIO;
 
+       if (c->stat.size) {
+               cap_size = ovl_getxattr(upperpath.dentry, XATTR_NAME_CAPS, &capability, &cap_size, 0);
+               if (cap_size < 0)
+                       return cap_size;
+       }
+
        err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
-       if (err)
+       if (err) {
+               kfree(capability);
                return err;
+       }
+
+       /*
+        * Writing to upper file will clear security.capability xattr. We
+        * don't want that to happen for normal copy-up operation.
+        */
+       if (capability) {
+               err = ovl_do_setxattr(upperpath.dentry, XATTR_NAME_CAPS, capability, cap_size, 0);
+               kfree(capability);
+               if (err)
+                       return err;
+       }
+
 
        err = vfs_removexattr(upperpath.dentry, OVL_XATTR_METACOPY);
        if (err)

If a file has been copied up metadata only, and later data is copied up, upper loses any security.capability xattr it has (underlying filesystem clears it as upon file write).

From a user's point of view, this is just a file copy-up and that should not result in losing security.capability xattr. Hence, before data copy up, save security.capability xattr (if any) and restore it on upper after data copy up is complete.

Signed-off-by Vivek Goyal <[email protected]>

Quoted 9 lines · Vivek Goyal

If a file has been copied up metadata only, and later data is copied up, upper loses any security.capability xattr it has (underlying filesystem clears it as upon file write).

From a user's point of view, this is just a file copy-up and that should not result in losing security.capability xattr. Hence, before data copy up, save security.capability xattr (if any) and restore it on upper after data copy up is complete.

Quoted 1 line

Signed-off-by Vivek Goyal <[email protected]>

Cleaned it up a bit. Hope I didn't break it...

Thanks,
Miklos

---
 fs/overlayfs/copy_up.c   |   27 +++++++++++++++++++++--
 fs/overlayfs/overlayfs.h |    2 +
 fs/overlayfs/util.c      |   55 +++++++++++++++++++++++++++++------------------
 3 files changed, 62 insertions(+), 22 deletions(-)

fs/overlayfs/util.c +35 -20

@@ -863,28 +863,49 @@ bool ovl_is_metacopy_dentry(struct dentr
 	return (oe->numlower > 1);
 }
 
-char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
+		     size_t padding)
 {
-	int res;
-	char *s, *next, *buf = NULL;
+	ssize_t res;
+	char *buf = NULL;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
+	res = vfs_getxattr(dentry, name, NULL, 0);
 	if (res < 0) {
 		if (res == -ENODATA || res == -EOPNOTSUPP)
-			return NULL;
+			return -ENODATA;
 		goto fail;
 	}
 
-	buf = kzalloc(res + padding + 1, GFP_KERNEL);
-	if (!buf)
-		return ERR_PTR(-ENOMEM);
+	if (res != 0) {
+		buf = kzalloc(res + padding, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+
+		res = vfs_getxattr(dentry, name, buf, res);
+		if (res < 0)
+			goto fail;
+	}
+	*value = buf;
 
-	if (res == 0)
-		goto invalid;
+	return res;
+
+fail:
+	pr_warn_ratelimited("overlayfs: failed to get xattr %s: err=%zi)\n",
+			    name, res);
+	kfree(buf);
+	return res;
+}
+
+char *ovl_get_redirect_xattr(struct dentry *dentry, int padding)
+{
+	int res;
+	char *s, *next, *buf = NULL;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
+	res = ovl_getxattr(dentry, OVL_XATTR_REDIRECT, &buf, padding + 1);
+	if (res == -ENODATA)
+		return NULL;
 	if (res < 0)
-		goto fail;
+		return ERR_PTR(res);
 	if (res == 0)
 		goto invalid;
 

@@ -900,15 +921,9 @@ char *ovl_get_redirect_xattr(struct dent
 	}
 
 	return buf;
-
-err_free:
-	kfree(buf);
-	return ERR_PTR(res);
-fail:
-	pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
-	goto err_free;
 invalid:
 	pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
 	res = -EINVAL;
-	goto err_free;
+	kfree(buf);
+	return ERR_PTR(res);
 }

fs/overlayfs/overlayfs.h +2 -0

@@ -277,6 +277,8 @@ int ovl_lock_rename_workdir(struct dentr
 int ovl_check_metacopy_xattr(struct dentry *dentry);
 bool ovl_is_metacopy_dentry(struct dentry *dentry);
 char *ovl_get_redirect_xattr(struct dentry *dentry, int padding);
+ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
+		     size_t padding);
 
 static inline bool ovl_is_impuredir(struct dentry *dentry)
 {

fs/overlayfs/copy_up.c +25 -2

@@ -742,6 +742,8 @@ static int ovl_copy_up_meta_inode_data(s
 {
 	struct path upperpath, datapath;
 	int err;
+	char *capability = NULL;
+	ssize_t uninitialized_var(cap_size);
 
 	ovl_path_upper(c->dentry, &upperpath);
 	if (WARN_ON(upperpath.dentry == NULL))

@@ -751,15 +753,36 @@ static int ovl_copy_up_meta_inode_data(s
 	if (WARN_ON(datapath.dentry == NULL))
 		return -EIO;
 
+	if (c->stat.size) {
+		err = cap_size = ovl_getxattr(upperpath.dentry, XATTR_NAME_CAPS,
+					      &capability, 0);
+		if (err < 0 && err != -ENODATA)
+			goto out;
+	}
+
 	err = ovl_copy_up_data(&datapath, &upperpath, c->stat.size);
 	if (err)
-		return err;
+		goto out_free;
+
+	/*
+	 * Writing to upper file will clear security.capability xattr. We
+	 * don't want that to happen for normal copy-up operation.
+	 */
+	if (capability) {
+		err = ovl_do_setxattr(upperpath.dentry, XATTR_NAME_CAPS, capability, cap_size, 0);
+		if (err)
+			goto out_free;
+	}
+
 
 	err = vfs_removexattr(upperpath.dentry, OVL_XATTR_METACOPY);
 	if (err)
-		return err;
+		goto out_free;
 
 	ovl_set_upperdata(d_inode(c->dentry));
+out_free:
+	kfree(capability);
+out:
 	return err;
 }