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bpf: Add BPF token delegation mount options to BPF FS
Add few new mount options to BPF FS that allow to specify that a given BPF FS instance allows creation of BPF token (added in the next patch), and what sort of operations are allowed under BPF token. As such, we get 4 new mount options, each is a bit mask - `delegate_cmds` allow to specify which bpf() syscall commands are allowed with BPF token derived from this BPF FS instance; - if BPF_MAP_CREATE command is allowed, `delegate_maps` specifies a set of allowable BPF map types that could be created with BPF token; - if BPF_PROG_LOAD command is allowed, `delegate_progs` specifies a set of allowable BPF program types that could be loaded with BPF token; - if BPF_PROG_LOAD command is allowed, `delegate_attachs` specifies a set of allowable BPF program attach types that could be loaded with BPF token; delegate_progs and delegate_attachs are meant to be used together, as full BPF program type is, in general, determined through both program type and program attach type. Currently, these mount options accept the following forms of values: - a special value "any", that enables all possible values of a given bit set; - numeric value (decimal or hexadecimal, determined by kernel automatically) that specifies a bit mask value directly; - all the values for a given mount option are combined, if specified multiple times. E.g., `mount -t bpf nodev /path/to/mount -o delegate_maps=0x1 -o delegate_maps=0x2` will result in a combined 0x3 mask. Ideally, more convenient (for humans) symbolic form derived from corresponding UAPI enums would be accepted (e.g., `-o delegate_progs=kprobe|tracepoint`) and I intend to implement this, but it requires a bunch of UAPI header churn, so I postponed it until this feature lands upstream or at least there is a definite consensus that this feature is acceptable and is going to make it, just to minimize amount of wasted effort and not increase amount of non-essential code to be reviewed. Attentive reader will notice that BPF FS is now marked as FS_USERNS_MOUNT, which theoretically makes it mountable inside non-init user namespace as long as the process has sufficient *namespaced* capabilities within that user namespace. But in reality we still restrict BPF FS to be mountable only by processes with CAP_SYS_ADMIN *in init userns* (extra check in bpf_fill_super()). FS_USERNS_MOUNT is added to allow creating BPF FS context object (i.e., fsopen("bpf")) from inside unprivileged process inside non-init userns, to capture that userns as the owning userns. It will still be required to pass this context object back to privileged process to instantiate and mount it. This manipulation is important, because capturing non-init userns as the owning userns of BPF FS instance (super block) allows to use that userns to constraint BPF token to that userns later on (see next patch). So creating BPF FS with delegation inside unprivileged userns will restrict derived BPF token objects to only "work" inside that intended userns, making it scoped to a intended "container". Also, setting these delegation options requires capable(CAP_SYS_ADMIN), so unprivileged process cannot set this up without involvement of a privileged process. There is a set of selftests at the end of the patch set that simulates this sequence of steps and validates that everything works as intended. But careful review is requested to make sure there are no missed gaps in the implementation and testing. This somewhat subtle set of aspects is the result of previous discussions ([0]) about various user namespace implications and interactions with BPF token functionality and is necessary to contain BPF token inside intended user namespace. [0] https://lore.kernel.org/bpf/20230704-hochverdient-lehne-eeb9eeef785e@brauner/ Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Christian Brauner <brauner@kernel.org> Link: https://lore.kernel.org/bpf/20240124022127.2379740-3-andrii@kernel.org
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@ -1609,6 +1609,18 @@ struct bpf_link_primer {
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u32 id;
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};
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struct bpf_mount_opts {
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kuid_t uid;
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kgid_t gid;
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umode_t mode;
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/* BPF token-related delegation options */
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u64 delegate_cmds;
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u64 delegate_maps;
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u64 delegate_progs;
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u64 delegate_attachs;
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};
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struct bpf_struct_ops_value;
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struct btf_member;
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@ -20,6 +20,7 @@
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#include <linux/filter.h>
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#include <linux/bpf.h>
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#include <linux/bpf_trace.h>
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#include <linux/kstrtox.h>
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#include "preload/bpf_preload.h"
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enum bpf_type {
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@ -601,6 +602,7 @@ static int bpf_show_options(struct seq_file *m, struct dentry *root)
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{
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struct inode *inode = d_inode(root);
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umode_t mode = inode->i_mode & S_IALLUGO & ~S_ISVTX;
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struct bpf_mount_opts *opts = root->d_sb->s_fs_info;
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if (!uid_eq(inode->i_uid, GLOBAL_ROOT_UID))
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seq_printf(m, ",uid=%u",
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@ -610,6 +612,26 @@ static int bpf_show_options(struct seq_file *m, struct dentry *root)
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from_kgid_munged(&init_user_ns, inode->i_gid));
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if (mode != S_IRWXUGO)
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seq_printf(m, ",mode=%o", mode);
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if (opts->delegate_cmds == ~0ULL)
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seq_printf(m, ",delegate_cmds=any");
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else if (opts->delegate_cmds)
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seq_printf(m, ",delegate_cmds=0x%llx", opts->delegate_cmds);
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if (opts->delegate_maps == ~0ULL)
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seq_printf(m, ",delegate_maps=any");
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else if (opts->delegate_maps)
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seq_printf(m, ",delegate_maps=0x%llx", opts->delegate_maps);
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if (opts->delegate_progs == ~0ULL)
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seq_printf(m, ",delegate_progs=any");
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else if (opts->delegate_progs)
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seq_printf(m, ",delegate_progs=0x%llx", opts->delegate_progs);
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if (opts->delegate_attachs == ~0ULL)
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seq_printf(m, ",delegate_attachs=any");
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else if (opts->delegate_attachs)
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seq_printf(m, ",delegate_attachs=0x%llx", opts->delegate_attachs);
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return 0;
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}
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@ -635,28 +657,31 @@ enum {
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OPT_UID,
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OPT_GID,
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OPT_MODE,
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OPT_DELEGATE_CMDS,
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OPT_DELEGATE_MAPS,
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OPT_DELEGATE_PROGS,
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OPT_DELEGATE_ATTACHS,
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};
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static const struct fs_parameter_spec bpf_fs_parameters[] = {
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fsparam_u32 ("uid", OPT_UID),
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fsparam_u32 ("gid", OPT_GID),
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fsparam_u32oct ("mode", OPT_MODE),
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fsparam_string ("delegate_cmds", OPT_DELEGATE_CMDS),
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fsparam_string ("delegate_maps", OPT_DELEGATE_MAPS),
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fsparam_string ("delegate_progs", OPT_DELEGATE_PROGS),
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fsparam_string ("delegate_attachs", OPT_DELEGATE_ATTACHS),
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{}
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};
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struct bpf_mount_opts {
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kuid_t uid;
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kgid_t gid;
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umode_t mode;
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};
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static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
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{
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struct bpf_mount_opts *opts = fc->fs_private;
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struct bpf_mount_opts *opts = fc->s_fs_info;
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struct fs_parse_result result;
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kuid_t uid;
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kgid_t gid;
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int opt;
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int opt, err;
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u64 msk;
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opt = fs_parse(fc, bpf_fs_parameters, param, &result);
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if (opt < 0) {
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@ -708,6 +733,28 @@ static int bpf_parse_param(struct fs_context *fc, struct fs_parameter *param)
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case OPT_MODE:
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opts->mode = result.uint_32 & S_IALLUGO;
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break;
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case OPT_DELEGATE_CMDS:
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case OPT_DELEGATE_MAPS:
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case OPT_DELEGATE_PROGS:
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case OPT_DELEGATE_ATTACHS:
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if (strcmp(param->string, "any") == 0) {
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msk = ~0ULL;
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} else {
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err = kstrtou64(param->string, 0, &msk);
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if (err)
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return err;
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}
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/* Setting delegation mount options requires privileges */
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if (msk && !capable(CAP_SYS_ADMIN))
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return -EPERM;
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switch (opt) {
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case OPT_DELEGATE_CMDS: opts->delegate_cmds |= msk; break;
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case OPT_DELEGATE_MAPS: opts->delegate_maps |= msk; break;
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case OPT_DELEGATE_PROGS: opts->delegate_progs |= msk; break;
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case OPT_DELEGATE_ATTACHS: opts->delegate_attachs |= msk; break;
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default: return -EINVAL;
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}
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break;
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}
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return 0;
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@ -784,10 +831,14 @@ static int populate_bpffs(struct dentry *parent)
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static int bpf_fill_super(struct super_block *sb, struct fs_context *fc)
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{
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static const struct tree_descr bpf_rfiles[] = { { "" } };
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struct bpf_mount_opts *opts = fc->fs_private;
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struct bpf_mount_opts *opts = sb->s_fs_info;
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struct inode *inode;
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int ret;
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/* Mounting an instance of BPF FS requires privileges */
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if (fc->user_ns != &init_user_ns && !capable(CAP_SYS_ADMIN))
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return -EPERM;
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ret = simple_fill_super(sb, BPF_FS_MAGIC, bpf_rfiles);
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if (ret)
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return ret;
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@ -811,7 +862,7 @@ static int bpf_get_tree(struct fs_context *fc)
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static void bpf_free_fc(struct fs_context *fc)
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{
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kfree(fc->fs_private);
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kfree(fc->s_fs_info);
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}
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static const struct fs_context_operations bpf_context_ops = {
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@ -835,17 +886,32 @@ static int bpf_init_fs_context(struct fs_context *fc)
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opts->uid = current_fsuid();
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opts->gid = current_fsgid();
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fc->fs_private = opts;
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/* start out with no BPF token delegation enabled */
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opts->delegate_cmds = 0;
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opts->delegate_maps = 0;
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opts->delegate_progs = 0;
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opts->delegate_attachs = 0;
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fc->s_fs_info = opts;
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fc->ops = &bpf_context_ops;
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return 0;
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}
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static void bpf_kill_super(struct super_block *sb)
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{
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struct bpf_mount_opts *opts = sb->s_fs_info;
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kill_litter_super(sb);
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kfree(opts);
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}
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static struct file_system_type bpf_fs_type = {
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.owner = THIS_MODULE,
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.name = "bpf",
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.init_fs_context = bpf_init_fs_context,
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.parameters = bpf_fs_parameters,
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.kill_sb = kill_litter_super,
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.kill_sb = bpf_kill_super,
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.fs_flags = FS_USERNS_MOUNT,
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};
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static int __init bpf_init(void)
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