From 1d03e5660711c40f79917054328e0dc6bcb879a3 Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Thu, 24 Jun 2021 12:18:09 +0200 Subject: [PATCH] virtiofsd: Don't allow file creation with FUSE_OPEN A well behaved FUSE client uses FUSE_CREATE to create files. It isn't supposed to pass O_CREAT along a FUSE_OPEN request, as documented in the "fuse_lowlevel.h" header : /** * Open a file * * Open flags are available in fi->flags. The following rules * apply. * * - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be * filtered out / handled by the kernel. But if the client happens to do it anyway, the server ends up passing this flag to open() without the mandatory mode_t 4th argument. Since open() is a variadic function, glibc will happily pass whatever it finds on the stack to the syscall. If this file is compiled with -D_FORTIFY_SOURCE=2, glibc will even detect that and abort: *** invalid openat64 call: O_CREAT or O_TMPFILE without mode ***: terminated Specifying O_CREAT with FUSE_OPEN is a protocol violation. Check this in do_open(), print out a message and return an error to the client, EINVAL like we already do when fuse_mbuf_iter_advance() fails. The FUSE filesystem doesn't currently support O_TMPFILE, but the very same would happen if O_TMPFILE was passed in a FUSE_OPEN request. Check that as well. Signed-off-by: Greg Kurz Message-Id: <20210624101809.48032-1-groug@kaod.org> Reviewed-by: Dr. David Alan Gilbert Signed-off-by: Dr. David Alan Gilbert --- tools/virtiofsd/fuse_lowlevel.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c index 7fe2cef1eb..3d725bcba2 100644 --- a/tools/virtiofsd/fuse_lowlevel.c +++ b/tools/virtiofsd/fuse_lowlevel.c @@ -1084,6 +1084,12 @@ static void do_open(fuse_req_t req, fuse_ino_t nodeid, return; } + /* File creation is handled by do_create() or do_mknod() */ + if (arg->flags & (O_CREAT | O_TMPFILE)) { + fuse_reply_err(req, EINVAL); + return; + } + memset(&fi, 0, sizeof(fi)); fi.flags = arg->flags; fi.kill_priv = arg->open_flags & FUSE_OPEN_KILL_SUIDGID;