fuse: add basic infrastructure to support idmappings

Add some preparational changes in fuse_get_req/fuse_force_creds
to handle idmappings.

Miklos suggested [1], [2] to change the meaning of in.h.uid/in.h.gid
fields when daemon declares support for idmapped mounts. In a new semantic,
we fill uid/gid values in fuse header with a id-mapped caller uid/gid (for
requests which create new inodes), for all the rest cases we just send -1
to userspace.

No functional changes intended.

Link: https://lore.kernel.org/all/CAJfpegsVY97_5mHSc06mSw79FehFWtoXT=hhTUK_E-Yhr7OAuQ@mail.gmail.com/
Link: https://lore.kernel.org/all/CAJfpegtHQsEUuFq1k4ZbTD3E1h-GsrN3PWyv7X8cg6sfU_W2Yw@mail.gmail.com/
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1b60882..b4092b3 100644 (file)
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -108,7 +108,9 @@ static void fuse_drop_waiting(struct fuse_conn *fc)
 
 static void fuse_put_request(struct fuse_req *req);
 
-static struct fuse_req *fuse_get_req(struct fuse_mount *fm, bool for_background)
+static struct fuse_req *fuse_get_req(struct mnt_idmap *idmap,
+                                    struct fuse_mount *fm,
+                                    bool for_background)
 {
        struct fuse_conn *fc = fm->fc;
        struct fuse_req *req;
@@ -140,19 +142,37 @@ static struct fuse_req *fuse_get_req(struct fuse_mount *fm, bool for_background)
                goto out;
        }
 
-       req->in.h.uid = from_kuid(fc->user_ns, current_fsuid());
-       req->in.h.gid = from_kgid(fc->user_ns, current_fsgid());
        req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 
        __set_bit(FR_WAITING, &req->flags);
        if (for_background)
                __set_bit(FR_BACKGROUND, &req->flags);
 
-       if (unlikely(req->in.h.uid == ((uid_t)-1) ||
-                    req->in.h.gid == ((gid_t)-1))) {
-               fuse_put_request(req);
-               return ERR_PTR(-EOVERFLOW);
+       if ((fm->sb->s_iflags & SB_I_NOIDMAP) || idmap) {
+               kuid_t idmapped_fsuid;
+               kgid_t idmapped_fsgid;
+
+               /*
+                * Note, that when
+                * (fm->sb->s_iflags & SB_I_NOIDMAP) is true, then
+                * (idmap == &nop_mnt_idmap) is always true and therefore,
+                * mapped_fsuid(idmap, fc->user_ns) == current_fsuid().
+                */
+               idmapped_fsuid = idmap ? mapped_fsuid(idmap, fc->user_ns) : current_fsuid();
+               idmapped_fsgid = idmap ? mapped_fsgid(idmap, fc->user_ns) : current_fsgid();
+               req->in.h.uid = from_kuid(fc->user_ns, idmapped_fsuid);
+               req->in.h.gid = from_kgid(fc->user_ns, idmapped_fsgid);
+
+               if (unlikely(req->in.h.uid == ((uid_t)-1) ||
+                            req->in.h.gid == ((gid_t)-1))) {
+                       fuse_put_request(req);
+                       return ERR_PTR(-EOVERFLOW);
+               }
+       } else {
+               req->in.h.uid = FUSE_INVALID_UIDGID;
+               req->in.h.gid = FUSE_INVALID_UIDGID;
        }
+
        return req;
 
  out:
@@ -497,8 +517,14 @@ static void fuse_force_creds(struct fuse_req *req)
 {
        struct fuse_conn *fc = req->fm->fc;
 
-       req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
-       req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
+       if (req->fm->sb->s_iflags & SB_I_NOIDMAP) {
+               req->in.h.uid = from_kuid_munged(fc->user_ns, current_fsuid());
+               req->in.h.gid = from_kgid_munged(fc->user_ns, current_fsgid());
+       } else {
+               req->in.h.uid = FUSE_INVALID_UIDGID;
+               req->in.h.gid = FUSE_INVALID_UIDGID;
+       }
+
        req->in.h.pid = pid_nr_ns(task_pid(current), fc->pid_ns);
 }
 
@@ -530,7 +556,7 @@ ssize_t fuse_simple_request(struct fuse_mount *fm, struct fuse_args *args)
                __set_bit(FR_FORCE, &req->flags);
        } else {
                WARN_ON(args->nocreds);
-               req = fuse_get_req(fm, false);
+               req = fuse_get_req(NULL, fm, false);
                if (IS_ERR(req))
                        return PTR_ERR(req);
        }
@@ -591,7 +617,7 @@ int fuse_simple_background(struct fuse_mount *fm, struct fuse_args *args,
                __set_bit(FR_BACKGROUND, &req->flags);
        } else {
                WARN_ON(args->nocreds);
-               req = fuse_get_req(fm, true);
+               req = fuse_get_req(NULL, fm, true);
                if (IS_ERR(req))
                        return PTR_ERR(req);
        }
@@ -613,7 +639,7 @@ static int fuse_simple_notify_reply(struct fuse_mount *fm,
        struct fuse_req *req;
        struct fuse_iqueue *fiq = &fm->fc->iq;
 
-       req = fuse_get_req(fm, false);
+       req = fuse_get_req(NULL, fm, false);
        if (IS_ERR(req))
                return PTR_ERR(req);
 

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index bebd890..ed53e17 100644 (file)
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1572,6 +1572,7 @@ static void fuse_sb_defaults(struct super_block *sb)
        sb->s_time_gran = 1;
        sb->s_export_op = &fuse_export_operations;
        sb->s_iflags |= SB_I_IMA_UNVERIFIABLE_SIGNATURE;
+       sb->s_iflags |= SB_I_NOIDMAP;
        if (sb->s_user_ns != &init_user_ns)
                sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
        sb->s_flags &= ~(SB_NOSEC | SB_I_VERSION);

diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index d08b99d..2ccf381 100644 (file)
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -984,6 +984,8 @@ struct fuse_fallocate_in {
  */
 #define FUSE_UNIQUE_RESEND (1ULL << 63)
 
+#define FUSE_INVALID_UIDGID ((uint32_t)(-1))
+
 struct fuse_in_header {
        uint32_t        len;
        uint32_t        opcode;