When posix access ACL is set, it can have an effect on file mode and
it can also need to clear SGID if.
- None of caller's group/supplementary groups match file owner group.
AND
- Caller is not priviliged (No CAP_FSETID).
As of now fuser server is responsible for changing the file mode as well. But
it does not know whether to clear SGID or not.
So add a flag FUSE_SETXATTR_ACL_KILL_SGID and send this info with
SETXATTR to let file server know that sgid needs to be cleared as well.
Reported-by: Luis Henriques <lhenriques@xxxxxxx>
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
fs/fuse/acl.c | 8 +++++++-
include/uapi/linux/fuse.h | 7 +++++++
2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/fs/fuse/acl.c b/fs/fuse/acl.c
index d31260a139d4..8819ceb0a4e5 100644
--- a/fs/fuse/acl.c
+++ b/fs/fuse/acl.c
@@ -71,6 +71,7 @@ int fuse_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
return -EINVAL;
if (acl) {
+ unsigned extra_flags = 0;
/*
* Fuse userspace is responsible for updating access
* permissions in the inode, if needed. fuse_setxattr
@@ -94,7 +95,12 @@ int fuse_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
return ret;
}
- ret = fuse_setxattr(inode, name, value, size, 0, 0);
+ if (fc->setxattr_v2 &&
+ !in_group_p(i_gid_into_mnt(&init_user_ns, inode)) &&
+ !capable_wrt_inode_uidgid(&init_user_ns, inode, CAP_FSETID))
+ extra_flags |= FUSE_SETXATTR_ACL_KILL_SGID;
+
+ ret = fuse_setxattr(inode, name, value, size, 0, extra_flags);
kfree(value);
} else {
ret = fuse_removexattr(inode, name);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 1bb555c1c117..08c11a7beaa7 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -180,6 +180,7 @@
* - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID
* - add FUSE_OPEN_KILL_SUIDGID
* - add FUSE_SETXATTR_V2
+ * - add FUSE_SETXATTR_ACL_KILL_SGID
*/
#ifndef _LINUX_FUSE_H
@@ -454,6 +455,12 @@ struct fuse_file_lock {
*/
#define FUSE_OPEN_KILL_SUIDGID (1 << 0)
+/**
+ * setxattr flags
+ * FUSE_SETXATTR_ACL_KILL_SGID: Clear SGID when system.posix_acl_access is set
+ */
+#define FUSE_SETXATTR_ACL_KILL_SGID (1 << 0)
+
enum fuse_opcode {
FUSE_LOOKUP = 1,
FUSE_FORGET = 2, /* no reply */
--
2.25.4
