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fuse: handle killpriv in userspace fs

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Only userspace filesystem can do the killing of suid/sgid without races.
So introduce an INIT flag and negotiate support for this.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Miklos Szeredi 2016-10-01 07:32:32 +02:00
parent a09f99edde
commit 5e940c1dd3
4 changed files with 40 additions and 20 deletions
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46
fs/fuse/dir.c
View file

@ -1703,6 +1703,7 @@ error:
static int fuse_setattr(struct dentry *entry, struct iattr *attr)
{
struct inode *inode = d_inode(entry);
struct fuse_conn *fc = get_fuse_conn(inode);
struct file *file = (attr->ia_valid & ATTR_FILE) ? attr->ia_file : NULL;
int ret;
@ -1710,27 +1711,36 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr)
return -EACCES;
if (attr->ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID)) {
int kill;
attr->ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID |
ATTR_MODE);
/*
* ia_mode calculation may have used stale i_mode. Refresh and
* recalculate.
*/
ret = fuse_do_getattr(inode, NULL, file);
if (ret)
return ret;
attr->ia_mode = inode->i_mode;
kill = should_remove_suid(entry);
if (kill & ATTR_KILL_SUID) {
attr->ia_valid |= ATTR_MODE;
attr->ia_mode &= ~S_ISUID;
}
if (kill & ATTR_KILL_SGID) {
attr->ia_valid |= ATTR_MODE;
attr->ia_mode &= ~S_ISGID;
/*
* The only sane way to reliably kill suid/sgid is to do it in
* the userspace filesystem
*
* This should be done on write(), truncate() and chown().
*/
if (!fc->handle_killpriv) {
int kill;
/*
* ia_mode calculation may have used stale i_mode.
* Refresh and recalculate.
*/
ret = fuse_do_getattr(inode, NULL, file);
if (ret)
return ret;
attr->ia_mode = inode->i_mode;
kill = should_remove_suid(entry);
if (kill & ATTR_KILL_SUID) {
attr->ia_valid |= ATTR_MODE;
attr->ia_mode &= ~S_ISUID;
}
if (kill & ATTR_KILL_SGID) {
attr->ia_valid |= ATTR_MODE;
attr->ia_mode &= ~S_ISGID;
}
}
}
if (!attr->ia_valid)

3
fs/fuse/fuse_i.h
View file

@ -547,6 +547,9 @@ struct fuse_conn {
/** allow parallel lookups and readdir (default is serialized) */
unsigned parallel_dirops:1;
/** handle fs handles killing suid/sgid/cap on write/chown/trunc */
unsigned handle_killpriv:1;
/*
* The following bitfields are only for optimization purposes
* and hence races in setting them will not cause malfunction

4
fs/fuse/inode.c
View file

@ -910,6 +910,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
fc->writeback_cache = 1;
if (arg->flags & FUSE_PARALLEL_DIROPS)
fc->parallel_dirops = 1;
if (arg->flags & FUSE_HANDLE_KILLPRIV)
fc->handle_killpriv = 1;
if (arg->time_gran && arg->time_gran <= 1000000000)
fc->sb->s_time_gran = arg->time_gran;
} else {
@ -941,7 +943,7 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
FUSE_FLOCK_LOCKS | FUSE_HAS_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT |
FUSE_PARALLEL_DIROPS;
FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV;
req->in.h.opcode = FUSE_INIT;
req->in.numargs = 1;
req->in.args[0].size = sizeof(*arg);

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

@ -108,6 +108,9 @@
*
* 7.25
* - add FUSE_PARALLEL_DIROPS
*
* 7.26
* - add FUSE_HANDLE_KILLPRIV
*/
#ifndef _LINUX_FUSE_H
@ -143,7 +146,7 @@
#define FUSE_KERNEL_VERSION 7
/** Minor version number of this interface */
#define FUSE_KERNEL_MINOR_VERSION 25
#define FUSE_KERNEL_MINOR_VERSION 26
/** The node ID of the root inode */
#define FUSE_ROOT_ID 1
@ -238,6 +241,7 @@ struct fuse_file_lock {
* FUSE_WRITEBACK_CACHE: use writeback cache for buffered writes
* FUSE_NO_OPEN_SUPPORT: kernel supports zero-message opens
* FUSE_PARALLEL_DIROPS: allow parallel lookups and readdir
* FUSE_HANDLE_KILLPRIV: fs handles killing suid/sgid/cap on write/chown/trunc
*/
#define FUSE_ASYNC_READ (1 << 0)
#define FUSE_POSIX_LOCKS (1 << 1)
@ -258,6 +262,7 @@ struct fuse_file_lock {
#define FUSE_WRITEBACK_CACHE (1 << 16)
#define FUSE_NO_OPEN_SUPPORT (1 << 17)
#define FUSE_PARALLEL_DIROPS (1 << 18)
#define FUSE_HANDLE_KILLPRIV (1 << 19)
/**
* CUSE INIT request/reply flags