[PATCH v4 02/15] fs/fuse: add basic infrastructure to support idmappings

Alexander Mikhalitsyn
2024-09-03T15:16:52Z

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/ [1]
Link: https://lore.kernel.org/all/CAJfpegtHQsEUuFq1k4ZbTD3E1h-GsrN3PWyv7X8cg6sfU_W2Yw@mail.gmail.com/ [2]
Cc: Christian Brauner <brauner@kernel.org>
Cc: Seth Forshee <sforshee@kernel.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Bernd Schubert <bschubert@ddn.com>
Cc: <linux-fsdevel@vger.kernel.org>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
---
v4:
- this commit added
---
fs/fuse/dev.c | 50 +++++++++++++++++++++++++++++----------
fs/fuse/inode.c | 1 +
include/uapi/linux/fuse.h | 2 ++
3 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 7146038b2fe7..d3f3c3557c04 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -103,7 +103,9 @@ 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;
@@ -135,19 +137,37 @@ 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:
@@ -466,8 +486,14 @@ 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);
}

@@ -499,7 +525,7 @@ 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);
}
@@ -560,7 +586,7 @@ 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);
}
@@ -583,7 +609,7 @@ static int fuse_simple_notify_reply(struct fuse_mount *fm,
struct fuse_iqueue *fiq = &fm->fc->iq;
int err = 0;

- 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 d8ab4e93916f..115538f6f283 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1567,6 +1567,7 @@ 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 d08b99d60f6f..2ccf38181df2 100644
--- 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;
--
2.34.1