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fuse: add a flag FUSE_SETXATTR_ACL_KILL_SGID to kill SGID

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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@suse.de>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Vivek Goyal 2021-03-25 11:18:23 -04:00 committed by Miklos Szeredi
parent 52a4c95f4d
commit 550a7d3bc0
2 changed files with 13 additions and 1 deletions
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7
fs/fuse/acl.c
View file

@ -71,6 +71,7 @@ int fuse_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
return -EINVAL;
if (acl) {
unsigned int extra_flags = 0;
/*
* Fuse userspace is responsible for updating access
* permissions in the inode, if needed. fuse_setxattr
@ -94,7 +95,11 @@ int fuse_set_acl(struct user_namespace *mnt_userns, struct inode *inode,
return ret;
}
ret = fuse_setxattr(inode, name, value, size, 0, 0);
if (!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);

7
include/uapi/linux/fuse.h
View file

@ -180,6 +180,7 @@
* - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID
* - add FUSE_OPEN_KILL_SUIDGID
* - extend fuse_setxattr_in, add FUSE_SETXATTR_EXT
* - 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 */