syzbot has reported a crash in a test case where overlayfs uses
hugetlbfs as upper fs.
Since hugetlbfs has no write() nor write_iter() file ops, there seems
to be little value in supporting this configuration, however, we do not
want to regress strange use cases that me be using such configuration.
As a minimum, check for this case and warn about it on mount time as
well as adding this check for the strict requirements set of remote
upper fs.
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/overlayfs/super.c | 60 ++++++++++++++++++++++++++++----------------
1 file changed, 39 insertions(+), 21 deletions(-)
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 91476bc422f9..5bee70eb8f64 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -6,6 +6,7 @@
#include <uapi/linux/magic.h>
#include <linux/fs.h>
+#include <linux/file.h>
#include <linux/namei.h>
#include <linux/xattr.h>
#include <linux/mount.h>
@@ -1131,42 +1132,61 @@ static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
}
/*
- * Returns 1 if RENAME_WHITEOUT is supported, 0 if not supported and
+ * Returns 1 if required ops are supported, 0 if not supported and
* negative values if error is encountered.
*/
-static int ovl_check_rename_whiteout(struct dentry *workdir)
+static int ovl_check_supported_ops(struct ovl_fs *ofs)
{
- struct inode *dir = d_inode(workdir);
- struct dentry *temp;
+ struct inode *dir = d_inode(ofs->workdir);
+ struct dentry *temp = NULL;
struct dentry *dest;
struct dentry *whiteout;
struct name_snapshot name;
+ struct path path;
+ struct file *file;
+ unsigned int unsupported;
int err;
inode_lock_nested(dir, I_MUTEX_PARENT);
- temp = ovl_create_temp(workdir, OVL_CATTR(S_IFREG | 0));
- err = PTR_ERR(temp);
- if (IS_ERR(temp))
+ path.mnt = ovl_upper_mnt(ofs);
+ path.dentry = ovl_create_temp(ofs->workdir, OVL_CATTR(S_IFREG | 0));
+ err = PTR_ERR(path.dentry);
+ if (IS_ERR(path.dentry))
goto out_unlock;
- dest = ovl_lookup_temp(workdir);
- err = PTR_ERR(dest);
- if (IS_ERR(dest)) {
- dput(temp);
+ temp = path.dentry;
+ file = dentry_open(&path, O_RDWR, current_cred());
+ err = PTR_ERR(file);
+ if (IS_ERR(file))
+ goto out_unlock;
+
+ unsupported = OVL_UPPER_FMODE_MASK & ~file->f_mode;
+ fput(file);
+ if (unsupported) {
+ err = 0;
+ pr_warn("upper fs does not support required file operations (%x).\n",
+ unsupported);
goto out_unlock;
}
+ dest = ovl_lookup_temp(ofs->workdir);
+ err = PTR_ERR(dest);
+ if (IS_ERR(dest))
+ goto out_unlock;
+
/* Name is inline and stable - using snapshot as a copy helper */
take_dentry_name_snapshot(&name, temp);
err = ovl_do_rename(dir, temp, dir, dest, RENAME_WHITEOUT);
if (err) {
- if (err == -EINVAL)
+ if (err == -EINVAL) {
err = 0;
+ pr_warn("upper fs does not support RENAME_WHITEOUT.\n");
+ }
goto cleanup_temp;
}
- whiteout = lookup_one_len(name.name.name, workdir, name.name.len);
+ whiteout = lookup_one_len(name.name.name, ofs->workdir, name.name.len);
err = PTR_ERR(whiteout);
if (IS_ERR(whiteout))
goto cleanup_temp;
@@ -1181,10 +1201,10 @@ static int ovl_check_rename_whiteout(struct dentry *workdir)
cleanup_temp:
ovl_cleanup(dir, temp);
release_dentry_name_snapshot(&name);
- dput(temp);
dput(dest);
out_unlock:
+ dput(temp);
inode_unlock(dir);
return err;
@@ -1195,7 +1215,7 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
{
struct vfsmount *mnt = ovl_upper_mnt(ofs);
struct dentry *temp;
- bool rename_whiteout;
+ bool supported_ops;
bool d_type;
int fh_type;
int err;
@@ -1235,14 +1255,12 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
pr_warn("upper fs does not support tmpfile.\n");
- /* Check if upper/work fs supports RENAME_WHITEOUT */
- err = ovl_check_rename_whiteout(ofs->workdir);
+ /* Check if upper/work fs supports required ops */
+ err = ovl_check_supported_ops(ofs);
if (err < 0)
goto out;
- rename_whiteout = err;
- if (!rename_whiteout)
- pr_warn("upper fs does not support RENAME_WHITEOUT.\n");
+ supported_ops = err;
/*
* Check if upper/work fs supports trusted.overlay.* xattr
@@ -1264,7 +1282,7 @@ static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
* we can enforce strict requirements for remote upper fs.
*/
if (ovl_dentry_remote(ofs->workdir) &&
- (!d_type || !rename_whiteout || ofs->noxattr)) {
+ (!d_type || !supported_ops || ofs->noxattr)) {
pr_err("upper fs missing required features.\n");
err = -EINVAL;
goto out;
--
2.17.1
