3 files changed, 49 insertions, 6 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index f127625543b4..65da6e1b6de5 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -411,17 +411,45 @@ int fuse_do_getattr(struct inode *inode)
         return err;
 }
 
+/*
+ * Calling into a user-controlled filesystem gives the filesystem
+ * daemon ptrace-like capabilities over the requester process.  This
+ * means, that the filesystem daemon is able to record the exact
+ * filesystem operations performed, and can also control the behavior
+ * of the requester process in otherwise impossible ways.  For example
+ * it can delay the operation for arbitrary length of time allowing
+ * DoS against the requester.
+ *
+ * For this reason only those processes can call into the filesystem,
+ * for which the owner of the mount has ptrace privilege.  This
+ * excludes processes started by other users, suid or sgid processes.
+ */
+static int fuse_allow_task(struct fuse_conn *fc, struct task_struct *task)
+{
+        if (fc->flags & FUSE_ALLOW_OTHER)
+                return 1;
+
+        if (task->euid == fc->user_id &&
+            task->suid == fc->user_id &&
+            task->uid == fc->user_id &&
+            task->egid == fc->group_id &&
+            task->sgid == fc->group_id &&
+            task->gid == fc->group_id)
+                return 1;
+
+        return 0;
+}
+
 static int fuse_revalidate(struct dentry *entry)
 {
         struct inode *inode = entry->d_inode;
         struct fuse_inode *fi = get_fuse_inode(inode);
         struct fuse_conn *fc = get_fuse_conn(inode);
 
-        if (get_node_id(inode) == FUSE_ROOT_ID) {
-                if (!(fc->flags & FUSE_ALLOW_OTHER) &&
-                    current->fsuid != fc->user_id)
-                        return -EACCES;
-        } else if (time_before_eq(jiffies, fi->i_time))
+        if (!fuse_allow_task(fc, current))
+                return -EACCES;
+        if (get_node_id(inode) != FUSE_ROOT_ID &&
+            time_before_eq(jiffies, fi->i_time))
                 return 0;
 
         return fuse_do_getattr(inode);
@@ -431,7 +459,7 @@ static int fuse_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
         struct fuse_conn *fc = get_fuse_conn(inode);
 
-        if (!(fc->flags & FUSE_ALLOW_OTHER) && current->fsuid != fc->user_id)
+        if (!fuse_allow_task(fc, current))
                 return -EACCES;
         else if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
                 int err = generic_permission(inode, mask, NULL);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index aff3a01ea02b..3ec2aff3fdb5 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -198,6 +198,9 @@ struct fuse_conn {
         /** The user id for this mount */
         uid_t user_id;
 
+        /** The group id for this mount */
+        gid_t group_id;
+
         /** The fuse mount flags for this mount */
         unsigned flags;
 
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0b75c73386e9..c8e54c0658f1 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -31,6 +31,7 @@ struct fuse_mount_data {
         int fd;
         unsigned rootmode;
         unsigned user_id;
+        unsigned group_id;
         unsigned flags;
         unsigned max_read;
 };
@@ -199,6 +200,7 @@ static void fuse_put_super(struct super_block *sb)
         spin_lock(&fuse_lock);
         fc->mounted = 0;
         fc->user_id = 0;
+        fc->group_id = 0;
         fc->flags = 0;
         /* Flush all readers on this fs */
         wake_up_all(&fc->waitq);
@@ -248,6 +250,7 @@ enum {
         OPT_FD,
         OPT_ROOTMODE,
         OPT_USER_ID,
+        OPT_GROUP_ID,
         OPT_DEFAULT_PERMISSIONS,
         OPT_ALLOW_OTHER,
         OPT_KERNEL_CACHE,
@@ -259,6 +262,7 @@ static match_table_t tokens = {
         {OPT_FD,                        "fd=%u"},
         {OPT_ROOTMODE,                  "rootmode=%o"},
         {OPT_USER_ID,                   "user_id=%u"},
+        {OPT_GROUP_ID,                  "group_id=%u"},
         {OPT_DEFAULT_PERMISSIONS,       "default_permissions"},
         {OPT_ALLOW_OTHER,               "allow_other"},
         {OPT_KERNEL_CACHE,              "kernel_cache"},
@@ -300,6 +304,12 @@ static int parse_fuse_opt(char *opt, struct fuse_mount_data *d)
                         d->user_id = value;
                         break;
 
+                case OPT_GROUP_ID:
+                        if (match_int(&args[0], &value))
+                                return 0;
+                        d->group_id = value;
+                        break;
+
                 case OPT_DEFAULT_PERMISSIONS:
                         d->flags |= FUSE_DEFAULT_PERMISSIONS;
                         break;
@@ -333,6 +343,7 @@ static int fuse_show_options(struct seq_file *m, struct vfsmount *mnt)
         struct fuse_conn *fc = get_fuse_conn_super(mnt->mnt_sb);
 
         seq_printf(m, ",user_id=%u", fc->user_id);
+        seq_printf(m, ",group_id=%u", fc->group_id);
         if (fc->flags & FUSE_DEFAULT_PERMISSIONS)
                 seq_puts(m, ",default_permissions");
         if (fc->flags & FUSE_ALLOW_OTHER)
@@ -465,6 +476,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 
         fc->flags = d.flags;
         fc->user_id = d.user_id;
+        fc->group_id = d.group_id;
         fc->max_read = d.max_read;
         if (fc->max_read / PAGE_CACHE_SIZE < fc->bdi.ra_pages)
                 fc->bdi.ra_pages = fc->max_read / PAGE_CACHE_SIZE;