FUSE_HANDLE_KILLPRIV flag says that file server will remove suid/sgid/caps
on truncate/chown/write.
But to be consistent with VFS behavior what we want is.
- caps are always cleared on chown/write/truncate
- suid is always cleared on chown, while for truncate/write it is cleared
only if caller does not have CAP_FSETID.
- sgid is always cleared on chown, while for truncate/write it is cleared
only if caller does not have CAP_FSETID as well as file has group execute
permission.
As previous flag did not provide above semantics. Implement a V2 of the
protocol with above said constraints.
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
---
fs/fuse/fuse_i.h | 6 ++++++
fs/fuse/inode.c | 5 ++++-
include/uapi/linux/fuse.h | 7 +++++++
3 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 740a8a7d7ae6..71bede0a57c9 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -610,6 +610,12 @@ struct fuse_conn {
/** cache READLINK responses in page cache */
unsigned cache_symlinks:1;
+ /** fs kills suid/sgid/cap on write/chown/trunc. suid is
+ killed on write/trunc only if caller did not have CAP_FSETID.
+ sgid is killed on write/truncate only if caller did not have
+ CAP_FSETID as well as file has group execute permission. */
+ unsigned handle_killpriv_v2:1;
+
/*
* The following bitfields are only for optimization purposes
* and hence races in setting them will not cause malfunction
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index bba747520e9b..113ba149e08d 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -965,6 +965,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_args *args,
min_t(unsigned int, FUSE_MAX_MAX_PAGES,
max_t(unsigned int, arg->max_pages, 1));
}
+ if (arg->flags & FUSE_HANDLE_KILLPRIV_V2)
+ fc->handle_killpriv_v2 = 1;
} else {
ra_pages = fc->max_read / PAGE_SIZE;
fc->no_lock = 1;
@@ -1002,7 +1004,8 @@ void fuse_send_init(struct fuse_conn *fc)
FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT |
FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
- FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA;
+ FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
+ FUSE_HANDLE_KILLPRIV_V2;
ia->args.opcode = FUSE_INIT;
ia->args.in_numargs = 1;
ia->args.in_args[0].size = sizeof(ia->in);
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 373cada89815..960ba8af5cf4 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -172,6 +172,7 @@
* - add FUSE_WRITE_KILL_PRIV flag
* - add FUSE_SETUPMAPPING and FUSE_REMOVEMAPPING
* - add map_alignment to fuse_init_out, add FUSE_MAP_ALIGNMENT flag
+ * - add FUSE_HANDLE_KILLPRIV_V2
*/
#ifndef _LINUX_FUSE_H
@@ -314,6 +315,11 @@ struct fuse_file_lock {
* FUSE_NO_OPENDIR_SUPPORT: kernel supports zero-message opendir
* FUSE_EXPLICIT_INVAL_DATA: only invalidate cached pages on explicit request
* FUSE_MAP_ALIGNMENT: map_alignment field is valid
+ * FUSE_HANDLE_KILLPRIV_V2: fs kills suid/sgid/cap on write/chown/trunc.
+ * Upon write/truncate suid/sgid is only killed if caller
+ * does not have CAP_FSETID. Additionally upon
+ * write/truncate sgid is killed only if file has group
+ * execute permission. (Same as Linux VFS behavior).
*/
#define FUSE_ASYNC_READ (1 << 0)
#define FUSE_POSIX_LOCKS (1 << 1)
@@ -342,6 +348,7 @@ struct fuse_file_lock {
#define FUSE_NO_OPENDIR_SUPPORT (1 << 24)
#define FUSE_EXPLICIT_INVAL_DATA (1 << 25)
#define FUSE_MAP_ALIGNMENT (1 << 26)
+#define FUSE_HANDLE_KILLPRIV_V2 (1 << 27)
/**
* CUSE INIT request/reply flags
--
2.25.4
