From 63f9909ff602082597849f684655e93336c50b11 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 9 Oct 2020 14:15:07 -0400 Subject: 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 --- include/uapi/linux/fuse.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 7233502ea991..29bd2e007947 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 -- cgit From 10c52c84e3f4872689a64ac7666b34d67e630691 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Wed, 11 Nov 2020 17:22:32 +0100 Subject: fuse: rename FUSE_WRITE_KILL_PRIV to FUSE_WRITE_KILL_SUIDGID Kernel has: ATTR_KILL_PRIV -> clear "security.capability" ATTR_KILL_SUID -> clear S_ISUID ATTR_KILL_SGID -> clear S_ISGID if executable Fuse has: FUSE_WRITE_KILL_PRIV -> clear S_ISUID and S_ISGID if executable So FUSE_WRITE_KILL_PRIV implies the complement of ATTR_KILL_PRIV, which is somewhat confusing. Also PRIV implies all privileges, including "security.capability". Change the name to FUSE_WRITE_KILL_SUIDGID and make FUSE_WRITE_KILL_PRIV an alias to perserve API compatibility Signed-off-by: Miklos Szeredi --- fs/fuse/file.c | 2 +- include/uapi/linux/fuse.h | 9 ++++++--- 2 files changed, 7 insertions(+), 4 deletions(-) (limited to 'include/uapi/linux') diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 41b1e14f3820..603af847d596 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1451,7 +1451,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter, if (write) { if (!capable(CAP_FSETID)) - ia->write.in.write_flags |= FUSE_WRITE_KILL_PRIV; + ia->write.in.write_flags |= FUSE_WRITE_KILL_SUIDGID; nres = fuse_send_write(ia, pos, nbytes, owner); } else { diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 29bd2e007947..2623c75b94a5 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -177,7 +177,7 @@ * - add flags to fuse_attr, add FUSE_ATTR_SUBMOUNT, add FUSE_SUBMOUNTS * * 7.33 - * - add FUSE_HANDLE_KILLPRIV_V2 + * - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID */ #ifndef _LINUX_FUSE_H @@ -387,11 +387,14 @@ struct fuse_file_lock { * * FUSE_WRITE_CACHE: delayed write from page cache, file handle is guessed * FUSE_WRITE_LOCKOWNER: lock_owner field is valid - * FUSE_WRITE_KILL_PRIV: kill suid and sgid bits + * FUSE_WRITE_KILL_SUIDGID: kill suid and sgid bits */ #define FUSE_WRITE_CACHE (1 << 0) #define FUSE_WRITE_LOCKOWNER (1 << 1) -#define FUSE_WRITE_KILL_PRIV (1 << 2) +#define FUSE_WRITE_KILL_SUIDGID (1 << 2) + +/* Obsolete alias; this flag implies killing suid/sgid only. */ +#define FUSE_WRITE_KILL_PRIV FUSE_WRITE_KILL_SUIDGID /** * Read flags -- cgit From 3179216135ec09825d7c7875580951a6e69dc5df Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 9 Oct 2020 14:15:09 -0400 Subject: fuse: setattr should set FATTR_KILL_SUIDGID 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 Signed-off-by: Miklos Szeredi --- fs/fuse/dir.c | 10 ++++++++++ include/uapi/linux/fuse.h | 3 ++- 2 files changed, 12 insertions(+), 1 deletion(-) (limited to 'include/uapi/linux') diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index c3e22a3dd323..28b07ae5e55f 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -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); diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 2623c75b94a5..9eb96e0564be 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -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 -- cgit From 643a666a89c358ef588d2b3ef9f2dc1efc421e61 Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Fri, 9 Oct 2020 14:15:11 -0400 Subject: fuse: add a flag FUSE_OPEN_KILL_SUIDGID for open() request With FUSE_HANDLE_KILLPRIV_V2 support, server will need to kill suid/sgid/ security.capability on open(O_TRUNC), if server supports FUSE_ATOMIC_O_TRUNC. But server needs to kill suid/sgid only if caller does not have CAP_FSETID. Given server does not have this information, client needs to send this info to server. So add a flag FUSE_OPEN_KILL_SUIDGID to fuse_open_in request which tells server to kill suid/sgid (only if group execute is set). This flag is added to the FUSE_OPEN request, as well as the FUSE_CREATE request if the create was non-exclusive, since that might result in an existing file being opened/truncated. Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/fuse/dir.c | 6 ++++++ fs/fuse/file.c | 6 ++++++ include/uapi/linux/fuse.h | 11 +++++++++-- 3 files changed, 21 insertions(+), 2 deletions(-) (limited to 'include/uapi/linux') diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index 778367d125f9..5d43af1169b7 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -541,6 +541,12 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry, inarg.flags = flags; inarg.mode = mode; inarg.umask = current_umask(); + + if (fm->fc->handle_killpriv_v2 && (flags & O_TRUNC) && + !(flags & O_EXCL) && !capable(CAP_FSETID)) { + inarg.open_flags |= FUSE_OPEN_KILL_SUIDGID; + } + args.opcode = FUSE_CREATE; args.nodeid = get_node_id(dir); args.in_numargs = 2; diff --git a/fs/fuse/file.c b/fs/fuse/file.c index aa0a44f7028f..349885353036 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -42,6 +42,12 @@ static int fuse_send_open(struct fuse_mount *fm, u64 nodeid, struct file *file, inarg.flags = file->f_flags & ~(O_CREAT | O_EXCL | O_NOCTTY); if (!fm->fc->atomic_o_trunc) inarg.flags &= ~O_TRUNC; + + if (fm->fc->handle_killpriv_v2 && + (inarg.flags & O_TRUNC) && !capable(CAP_FSETID)) { + inarg.open_flags |= FUSE_OPEN_KILL_SUIDGID; + } + args.opcode = opcode; args.nodeid = nodeid; args.in_numargs = 1; diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 9eb96e0564be..98ca64d1beb6 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -178,6 +178,7 @@ * * 7.33 * - add FUSE_HANDLE_KILLPRIV_V2, FUSE_WRITE_KILL_SUIDGID, FATTR_KILL_SUIDGID + * - add FUSE_OPEN_KILL_SUIDGID */ #ifndef _LINUX_FUSE_H @@ -444,6 +445,12 @@ struct fuse_file_lock { */ #define FUSE_ATTR_SUBMOUNT (1 << 0) +/** + * Open flags + * FUSE_OPEN_KILL_SUIDGID: Kill suid and sgid if executable + */ +#define FUSE_OPEN_KILL_SUIDGID (1 << 0) + enum fuse_opcode { FUSE_LOOKUP = 1, FUSE_FORGET = 2, /* no reply */ @@ -605,14 +612,14 @@ struct fuse_setattr_in { struct fuse_open_in { uint32_t flags; - uint32_t unused; + uint32_t open_flags; /* FUSE_OPEN_... */ }; struct fuse_create_in { uint32_t flags; uint32_t mode; uint32_t umask; - uint32_t padding; + uint32_t open_flags; /* FUSE_OPEN_... */ }; struct fuse_open_out { -- cgit