fuse2fs: fix group membership checking in op_chmod

In the decade or so since I touched fuse2fs, libfuse3 has grown the
ability to read the group ids of a process making a chmod request.  So
now we actually /can/ determine if a file's gid is a in the group list
of the process that initiated a fuse request.  Let's implement that too.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/174786678066.1383760.15547379523110361909.stgit@frogsfrogsfrogs
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/misc/fuse2fs.c b/misc/fuse2fs.c
index c65f312..4fa000e 100644 (file)
--- a/misc/fuse2fs.c
+++ b/misc/fuse2fs.c
@@ -2066,6 +2066,70 @@ out:
        return ret;
 }
 
+#if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 0)
+/* Obtain group ids of the process that sent us a command(?) */
+static int get_req_groups(struct fuse2fs *ff, gid_t **gids, size_t *nr_gids)
+{
+       ext2_filsys fs = ff->fs;
+       errcode_t err;
+       gid_t *array;
+       int nr = 32;    /* nobody has more than 32 groups right? */
+       int ret;
+
+       do {
+               err = ext2fs_get_array(nr, sizeof(gid_t), &array);
+               if (err)
+                       return translate_error(fs, 0, err);
+
+               ret = fuse_getgroups(nr, array);
+               if (ret < 0)
+                       return ret;
+
+               if (ret <= nr) {
+                       *gids = array;
+                       *nr_gids = ret;
+                       return 0;
+               }
+
+               ext2fs_free_mem(&array);
+               nr = ret;
+       } while (0);
+
+       /* shut up gcc */
+       return -ENOMEM;
+}
+
+/*
+ * Is this file's group id in the set of groups associated with the process
+ * that initiated the fuse request?  Returns 1 for yes, 0 for no, or a negative
+ * errno.
+ */
+static int in_file_group(struct fuse_context *ctxt,
+                        const struct ext2_inode_large *inode)
+{
+       struct fuse2fs *ff = (struct fuse2fs *)ctxt->private_data;
+       gid_t *gids = NULL;
+       size_t i, nr_gids = 0;
+       gid_t gid = inode_gid(*inode);
+       int ret;
+
+       ret = get_req_groups(ff, &gids, &nr_gids);
+       if (ret < 0)
+               return ret;
+
+       for (i = 0; i < nr_gids; i++)
+               if (gids[i] == gid)
+                       return 1;
+       return 0;
+}
+#else
+static int in_file_group(struct fuse_context *ctxt,
+                        const struct ext2_inode_large *inode)
+{
+       return ctxt->gid == inode_gid(*inode);
+}
+#endif
+
 static int op_chmod(const char *path, mode_t mode
 #if FUSE_VERSION >= FUSE_MAKE_VERSION(3, 0)
                        , struct fuse_file_info *fi EXT2FS_ATTR((unused))
@@ -2112,11 +2176,21 @@ static int op_chmod(const char *path, mode_t mode
         * of the user's groups, but FUSE only tells us about the primary
         * group.
         */
-       if (!is_superuser(ff, ctxt) && ctxt->gid != inode_gid(inode))
-               mode &= ~S_ISGID;
+       if (!is_superuser(ff, ctxt)) {
+               ret = in_file_group(ctxt, &inode);
+               if (ret < 0)
+                       goto out;
+
+               if (!ret)
+                       mode &= ~S_ISGID;
+       }
 
        inode.i_mode &= ~0xFFF;
        inode.i_mode |= mode & 0xFFF;
+
+       dbg_printf(ff, "%s: path=%s new_mode=0%o ino=%d\n", __func__,
+                  path, inode.i_mode, ino);
+
        ret = update_ctime(fs, ino, &inode);
        if (ret)
                goto out;