[PATCH 07/25] virtiofsd: validate path components

[Dr. David Alan Gilbert (git)]

From: Stefan Hajnoczi <address@hidden>

Several FUSE requests contain single path components.  A correct FUSE
client sends well-formed path components but there is currently no input
validation in case something went wrong or the client is malicious.

Refuse ".", "..", and paths containing '/' when we expect a path
component.

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 contrib/virtiofsd/passthrough_ll.c | 59 +++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 6 deletions(-)

diff --git a/contrib/virtiofsd/passthrough_ll.c 
b/contrib/virtiofsd/passthrough_ll.c
index 9f84419816..702fedc38a 100644
--- a/contrib/virtiofsd/passthrough_ll.c
+++ b/contrib/virtiofsd/passthrough_ll.c
@@ -146,6 +146,21 @@ static void unref_inode(struct lo_data *lo, struct 
lo_inode *inode, uint64_t n);
 
 static struct lo_inode *lo_find(struct lo_data *lo, struct stat *st);
 
+static int is_dot_or_dotdot(const char *name)
+{
+       return name[0] == '.' && (name[1] == '\0' ||
+                                 (name[1] == '.' && name[2] == '\0'));
+}
+
+/* Is `path` a single path component that is not "." or ".."? */
+static int is_safe_path_component(const char *path)
+{
+       if (strchr(path, '/')) {
+               return 0;
+       }
+
+       return !is_dot_or_dotdot(path);
+}
 
 static struct lo_data *lo_data(fuse_req_t req)
 {
@@ -657,6 +672,14 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, 
const char *name)
                fuse_log(FUSE_LOG_DEBUG, "lo_lookup(parent=%" PRIu64 ", 
name=%s)\n",
                        parent, name);
 
+       /* Don't use is_safe_path_component(), allow "." and ".." for NFS export
+        * support.
+        */
+       if (strchr(name, '/')) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        err = lo_do_lookup(req, parent, name, &e);
        if (err)
                fuse_reply_err(req, err);
@@ -719,6 +742,11 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t 
parent,
        struct fuse_entry_param e;
        struct lo_cred old = {};
 
+       if (!is_safe_path_component(name)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        dir = lo_inode(req, parent);
        if (!dir) {
                fuse_reply_err(req, EBADF);
@@ -815,6 +843,11 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, 
fuse_ino_t parent,
        struct fuse_entry_param e;
        int saverr;
 
+       if (!is_safe_path_component(name)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        inode = lo_inode(req, ino);
        if (!inode) {
                fuse_reply_err(req, EBADF);
@@ -854,6 +887,10 @@ out_err:
 static void lo_rmdir(fuse_req_t req, fuse_ino_t parent, const char *name)
 {
        int res;
+       if (!is_safe_path_component(name)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
 
        res = unlinkat(lo_fd(req, parent), name, AT_REMOVEDIR);
 
@@ -866,6 +903,12 @@ static void lo_rename(fuse_req_t req, fuse_ino_t parent, 
const char *name,
 {
        int res;
 
+       if (!is_safe_path_component(name) ||
+               !is_safe_path_component(newname)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        if (flags) {
                fuse_reply_err(req, EINVAL);
                return;
@@ -881,6 +924,11 @@ static void lo_unlink(fuse_req_t req, fuse_ino_t parent, 
const char *name)
 {
        int res;
 
+       if (!is_safe_path_component(name)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        res = unlinkat(lo_fd(req, parent), name, 0);
 
        fuse_reply_err(req, res == -1 ? errno : 0);
@@ -1031,12 +1079,6 @@ out_err:
        fuse_reply_err(req, error);
 }
 
-static int is_dot_or_dotdot(const char *name)
-{
-       return name[0] == '.' && (name[1] == '\0' ||
-                                 (name[1] == '.' && name[2] == '\0'));
-}
-
 static void lo_do_readdir(fuse_req_t req, fuse_ino_t ino, size_t size,
                          off_t offset, struct fuse_file_info *fi, int plus)
 {
@@ -1179,6 +1221,11 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, 
const char *name,
                fuse_log(FUSE_LOG_DEBUG, "lo_create(parent=%" PRIu64 ", 
name=%s)\n",
                        parent, name);
 
+       if (!is_safe_path_component(name)) {
+               fuse_reply_err(req, EINVAL);
+               return;
+       }
+
        err = lo_change_cred(req, &old);
        if (err)
                goto out;
-- 
2.23.0