From 63f9909ff602082597849f684655e93336c50b11 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 9 Oct 2020 14:15:07 -0400 Subject: [PATCH] fuse: introduce the notion of FUSE_HANDLE_KILLPRIV_V2 We already have FUSE_HANDLE_KILLPRIV flag that says that file server will remove suid/sgid/caps on truncate/chown/write. But that's little different from what Linux VFS implements. To be consistent with Linux 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. Server does not know if caller has CAP_FSETID or not. So for the case of write()/truncate(), client will send information in special flag to indicate whether to kill priviliges or not. These changes are in subsequent patches. FUSE_HANDLE_KILLPRIV_V2 relies on WRITE being sent to server to clear suid/sgid/security.capability. But with ->writeback_cache, WRITES are cached in guest. So it is not recommended to use FUSE_HANDLE_KILLPRIV_V2 and writeback_cache together. Though it probably might be good enough for lot of use cases. Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/fuse/fuse_i.h | 8 ++++++++ fs/fuse/inode.c | 5 ++++- include/uapi/linux/fuse.h | 11 ++++++++++- 3 files changed, 22 insertions(+), 2 deletions(-) diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index 8301c50..d414c78 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -636,6 +636,14 @@ struct fuse_conn { unsigned int legacy_opts_show: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 e7e9005..5a6102c 100644 --- a/fs/fuse/inode.c +++ b/fs/fuse/inode.c @@ -1038,6 +1038,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args, !fuse_dax_check_alignment(fc, arg->map_alignment)) { ok = false; } + if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) + fc->handle_killpriv_v2 = 1; } else { ra_pages = fc->max_read / PAGE_SIZE; fc->no_lock = 1; @@ -1080,7 +1082,8 @@ void fuse_send_init(struct fuse_mount *fm) 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; #ifdef CONFIG_FUSE_DAX if (fm->fc->dax) ia->in.flags |= FUSE_MAP_ALIGNMENT; diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 7233502..29bd2e0 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -175,6 +175,9 @@ * * 7.32 * - add flags to fuse_attr, add FUSE_ATTR_SUBMOUNT, add FUSE_SUBMOUNTS + * + * 7.33 + * - add FUSE_HANDLE_KILLPRIV_V2 */ #ifndef _LINUX_FUSE_H @@ -210,7 +213,7 @@ #define FUSE_KERNEL_VERSION 7 /** Minor version number of this interface */ -#define FUSE_KERNEL_MINOR_VERSION 32 +#define FUSE_KERNEL_MINOR_VERSION 33 /** The node ID of the root inode */ #define FUSE_ROOT_ID 1 @@ -320,6 +323,11 @@ struct fuse_file_lock { * foffset and moffset fields in struct * fuse_setupmapping_out and fuse_removemapping_one. * FUSE_SUBMOUNTS: kernel supports auto-mounting directory submounts + * 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) @@ -349,6 +357,7 @@ struct fuse_file_lock { #define FUSE_EXPLICIT_INVAL_DATA (1 << 25) #define FUSE_MAP_ALIGNMENT (1 << 26) #define FUSE_SUBMOUNTS (1 << 27) +#define FUSE_HANDLE_KILLPRIV_V2 (1 << 28) /** * CUSE INIT request/reply flags -- 2.7.4