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fuse: setattr should set FATTR_KILL_SUIDGID

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If fc->handle_killpriv_v2 is enabled, we expect file server to clear
suid/sgid/security.capbility upon chown/truncate/write as appropriate.

Upon truncate (ATTR_SIZE), suid/sgid are cleared only if caller does not
have CAP_FSETID.  File server does not know whether caller has CAP_FSETID
or not.  Hence set FATTR_KILL_SUIDGID upon truncate to let file server know
that caller does not have CAP_FSETID and it should kill suid/sgid as
appropriate.

On chown (ATTR_UID/ATTR_GID) suid/sgid need to be cleared irrespective of
capabilities of calling process, so set FATTR_KILL_SUIDGID unconditionally
in that case.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Vivek Goyal 2020-10-09 14:15:09 -04:00 committed by Miklos Szeredi
parent b866739596
commit 3179216135
2 changed files with 12 additions and 1 deletions
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10
fs/fuse/dir.c
View file

@ -1648,10 +1648,20 @@ int fuse_do_setattr(struct dentry *dentry, struct iattr *attr,
inarg.valid |= FATTR_FH;
inarg.fh = ff->fh;
}
/* Kill suid/sgid for non-directory chown unconditionally */
if (fc->handle_killpriv_v2 && !S_ISDIR(inode->i_mode) &&
attr->ia_valid & (ATTR_UID | ATTR_GID))
inarg.valid |= FATTR_KILL_SUIDGID;
if (attr->ia_valid & ATTR_SIZE) {
/* For mandatory locking in truncate */
inarg.valid |= FATTR_LOCKOWNER;
inarg.lock_owner = fuse_lock_owner_id(fc, current->files);
/* Kill suid/sgid for truncate only if no CAP_FSETID */
if (fc->handle_killpriv_v2 && !capable(CAP_FSETID))
inarg.valid |= FATTR_KILL_SUIDGID;
}
fuse_setattr_fill(fc, &args, inode, &inarg, &outarg);
err = fuse_simple_request(fm, &args);

3
include/uapi/linux/fuse.h
View file

@ -177,7 +177,7 @@
* - add flags to fuse_attr, add FUSE_ATTR_SUBMOUNT, add FUSE_SUBMOUNTS
*
* 7.33
* - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID
* - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID
*/
#ifndef _LINUX_FUSE_H
@ -274,6 +274,7 @@ struct fuse_file_lock {
#define FATTR_MTIME_NOW (1 << 8)
#define FATTR_LOCKOWNER (1 << 9)
#define FATTR_CTIME (1 << 10)
#define FATTR_KILL_SUIDGID (1 << 11)
/**
* Flags returned by the OPEN request