bpf: allow for mount options to specify permissions

Since we recently converted the BPF filesystem over to use mount_nodev(),
we now have the possibility to also hold mount options in sb's s_fs_info.
This work implements mount options support for specifying permissions on
the sb's inode, which will be used by tc when it manually needs to mount
the fs.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 2565809..0b030c9 100644 (file)
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -18,6 +18,7 @@
 #include <linux/namei.h>
 #include <linux/fs.h>
 #include <linux/kdev_t.h>
+#include <linux/parser.h>
 #include <linux/filter.h>
 #include <linux/bpf.h>
 
@@ -364,15 +365,66 @@ static void bpf_evict_inode(struct inode *inode)
 static const struct super_operations bpf_super_ops = {
        .statfs         = simple_statfs,
        .drop_inode     = generic_delete_inode,
+       .show_options   = generic_show_options,
        .evict_inode    = bpf_evict_inode,
 };
 
+enum {
+       OPT_MODE,
+       OPT_ERR,
+};
+
+static const match_table_t bpf_mount_tokens = {
+       { OPT_MODE, "mode=%o" },
+       { OPT_ERR, NULL },
+};
+
+struct bpf_mount_opts {
+       umode_t mode;
+};
+
+static int bpf_parse_options(char *data, struct bpf_mount_opts *opts)
+{
+       substring_t args[MAX_OPT_ARGS];
+       int option, token;
+       char *ptr;
+
+       opts->mode = S_IRWXUGO;
+
+       while ((ptr = strsep(&data, ",")) != NULL) {
+               if (!*ptr)
+                       continue;
+
+               token = match_token(ptr, bpf_mount_tokens, args);
+               switch (token) {
+               case OPT_MODE:
+                       if (match_octal(&args[0], &option))
+                               return -EINVAL;
+                       opts->mode = option & S_IALLUGO;
+                       break;
+               /* We might like to report bad mount options here, but
+                * traditionally we've ignored all mount options, so we'd
+                * better continue to ignore non-existing options for bpf.
+                */
+               }
+       }
+
+       return 0;
+}
+
 static int bpf_fill_super(struct super_block *sb, void *data, int silent)
 {
        static struct tree_descr bpf_rfiles[] = { { "" } };
+       struct bpf_mount_opts opts;
        struct inode *inode;
        int ret;
 
+       save_mount_options(sb, data);
+
+       ret = bpf_parse_options(data, &opts);
+       if (ret)
+               return ret;
+
        ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
        if (ret)
                return ret;
@@ -382,7 +434,7 @@ static int bpf_fill_super(struct super_block *sb, void *data, int silent)
        inode = sb->s_root->d_inode;
        inode->i_op = &bpf_dir_iops;
        inode->i_mode &= ~S_IALLUGO;
-       inode->i_mode |= S_ISVTX | S_IRWXUGO;
+       inode->i_mode |= S_ISVTX | opts.mode;
 
        return 0;
 }