bpf: Re-support uid and gid when mounting bpffs

For a clean, conflict-free revert of the token-related patches in commit
d17aff807f84 ("Revert BPF token-related functionality"), the bpf fs commit
750e785796bb ("bpf: Support uid and gid when mounting bpffs") was undone
temporarily as well.

This patch manually re-adds the functionality from the original one back
in 750e785796bb, no other functional changes intended.

Testing:

  # mount -t bpf -o uid=65534,gid=65534 bpffs ./foo
  # ls -la . | grep foo
  drwxrwxrwt   2 nobody nogroup          0 Dec 20 13:16 foo
  # mount -t bpf
  bpffs on /root/foo type bpf (rw,relatime,uid=65534,gid=65534)

Also, passing invalid arguments for uid/gid are properly rejected as expected.

Fixes: d17aff807f84 ("Revert BPF token-related functionality")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Cc: Jie Jiang <jiejiang@chromium.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Link: https://lore.kernel.org/bpf/20231220133805.20953-1-daniel@iogearbox.net

diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 1aafb2ff2e953c1a760f7e72f26de2bd966ac4de..41e0a55c35f5d19ccfc44d6978215c14e0590c9e 100644 (file)
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -599,8 +599,15 @@ EXPORT_SYMBOL(bpf_prog_get_type_path);
  */
 static int bpf_show_options(struct seq_file *m, struct dentry *root)
 {
-       umode_t mode = d_inode(root)->i_mode & S_IALLUGO & ~S_ISVTX;
-
+       struct inode *inode = d_inode(root);
+       umode_t mode = inode->i_mode & S_IALLUGO & ~S_ISVTX;
+
+       if (!uid_eq(inode->i_uid, GLOBAL_ROOT_UID))
+               seq_printf(m, ",uid=%u",
+                          from_kuid_munged(&init_user_ns, inode->i_uid));
+       if (!gid_eq(inode->i_gid, GLOBAL_ROOT_GID))
+               seq_printf(m, ",gid=%u",
+                          from_kgid_munged(&init_user_ns, inode->i_gid));
        if (mode != S_IRWXUGO)
                seq_printf(m, ",mode=%o", mode);
        return 0;
@@ -625,15 +632,21 @@ static const struct super_operations bpf_super_ops = {
 };
 
 enum {
+       OPT_UID,
+       OPT_GID,
        OPT_MODE,
 };
 
 static const struct fs_parameter_spec bpf_fs_parameters[] = {
+       fsparam_u32     ("uid",                         OPT_UID),
+       fsparam_u32     ("gid",                         OPT_GID),
        fsparam_u32oct  ("mode",                        OPT_MODE),
        {}
 };
 
 struct bpf_mount_opts {
+       kuid_t uid;
+       kgid_t gid;
        umode_t mode;
 };
 
@@ -641,6 +654,8 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
        struct bpf_mount_opts *opts = fc->fs_private;
        struct fs_parse_result result;
+       kuid_t uid;
+       kgid_t gid;
        int opt;
 
        opt = fs_parse(fc, bpf_fs_parameters, param, &result);
@@ -662,12 +677,42 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
        }
 
        switch (opt) {
+       case OPT_UID:
+               uid = make_kuid(current_user_ns(), result.uint_32);
+               if (!uid_valid(uid))
+                       goto bad_value;
+
+               /*
+                * The requested uid must be representable in the
+                * filesystem's idmapping.
+                */
+               if (!kuid_has_mapping(fc->user_ns, uid))
+                       goto bad_value;
+
+               opts->uid = uid;
+               break;
+       case OPT_GID:
+               gid = make_kgid(current_user_ns(), result.uint_32);
+               if (!gid_valid(gid))
+                       goto bad_value;
+
+               /*
+                * The requested gid must be representable in the
+                * filesystem's idmapping.
+                */
+               if (!kgid_has_mapping(fc->user_ns, gid))
+                       goto bad_value;
+
+               opts->gid = gid;
+               break;
        case OPT_MODE:
                opts->mode = result.uint_32 & S_IALLUGO;
                break;
        }
 
        return 0;
+bad_value:
+       return invalfc(fc, "Bad value for '%s'", param->key);
 }
 
 struct bpf_preload_ops *bpf_preload_ops;
@@ -750,6 +795,8 @@ static int bpf_fill_super(struct super_block *sb, struct fs_context *fc)
        sb->s_op = &bpf_super_ops;
 
        inode = sb->s_root->d_inode;
+       inode->i_uid = opts->uid;
+       inode->i_gid = opts->gid;
        inode->i_op = &bpf_dir_iops;
        inode->i_mode &= ~S_IALLUGO;
        populate_bpffs(sb->s_root);
@@ -785,6 +832,8 @@ static int bpf_init_fs_context(struct fs_context *fc)
                return -ENOMEM;
 
        opts->mode = S_IRWXUGO;
+       opts->uid = current_fsuid();
+       opts->gid = current_fsgid();
 
        fc->fs_private = opts;
        fc->ops = &bpf_context_ops;