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6e7d01 |
From cc9a776fba8ec62c862db55753107f19459dafa8 Mon Sep 17 00:00:00 2001
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6e7d01 |
From: Jon Maloy <jmaloy@redhat.com>
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6e7d01 |
Date: Tue, 9 Feb 2021 23:14:56 -0500
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6e7d01 |
Subject: [PATCH 3/3] virtiofsd: prevent opening of special files
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6e7d01 |
(CVE-2020-35517)
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6e7d01 |
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6e7d01 |
RH-Author: Jon Maloy <jmaloy@redhat.com>
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6e7d01 |
Message-id: <20210209231456.1555472-4-jmaloy@redhat.com>
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6e7d01 |
Patchwork-id: 101023
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6e7d01 |
O-Subject: [RHEL-8.4.0 qemu-kvm PATCH 3/3] virtiofsd: prevent opening of special files (CVE-2020-35517)
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6e7d01 |
Bugzilla: 1919111
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6e7d01 |
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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6e7d01 |
RH-Acked-by: Greg Kurz <gkurz@redhat.com>
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6e7d01 |
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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6e7d01 |
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6e7d01 |
From: Stefan Hajnoczi <stefanha@redhat.com>
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6e7d01 |
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6e7d01 |
A well-behaved FUSE client does not attempt to open special files with
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6e7d01 |
FUSE_OPEN because they are handled on the client side (e.g. device nodes
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6e7d01 |
are handled by client-side device drivers).
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6e7d01 |
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6e7d01 |
The check to prevent virtiofsd from opening special files is missing in
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6e7d01 |
a few cases, most notably FUSE_OPEN. A malicious client can cause
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6e7d01 |
virtiofsd to open a device node, potentially allowing the guest to
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6e7d01 |
escape. This can be exploited by a modified guest device driver. It is
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6e7d01 |
not exploitable from guest userspace since the guest kernel will handle
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6e7d01 |
special files inside the guest instead of sending FUSE requests.
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6e7d01 |
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6e7d01 |
This patch fixes this issue by introducing the lo_inode_open() function
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6e7d01 |
to check the file type before opening it. This is a short-term solution
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6e7d01 |
because it does not prevent a compromised virtiofsd process from opening
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6e7d01 |
device nodes on the host.
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6e7d01 |
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6e7d01 |
Restructure lo_create() to try O_CREAT | O_EXCL first. Note that O_CREAT
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6e7d01 |
| O_EXCL does not follow symlinks, so O_NOFOLLOW masking is not
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6e7d01 |
necessary here. If the file exists and the user did not specify O_EXCL,
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6e7d01 |
open it via lo_do_open().
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6e7d01 |
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6e7d01 |
Reported-by: Alex Xu <alex@alxu.ca>
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6e7d01 |
Fixes: CVE-2020-35517
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6e7d01 |
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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6e7d01 |
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
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6e7d01 |
Reviewed-by: Greg Kurz <groug@kaod.org>
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6e7d01 |
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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6e7d01 |
Message-Id: <20210204150208.367837-4-stefanha@redhat.com>
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6e7d01 |
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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6e7d01 |
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6e7d01 |
(cherry picked from commit a3fdbbc7f271bff7d53d0501b29d910ece0b3789)
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6e7d01 |
Signed-off-by: Jon Maloy <jmaloy@redhat.com>
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6e7d01 |
Signed-off-by: Jon Maloy <jmaloy.redhat.com>
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6e7d01 |
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6e7d01 |
tools/virtiofsd/passthrough_ll.c | 144 ++++++++++++++++++++
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6e7d01 |
1 file changed, 92 insertions(+), 52 deletions(-)
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6e7d01 |
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6e7d01 |
diff
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6e7d01 |
index e5bd3d73e4..cb0992f2db 100644
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6e7d01 |
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6e7d01 |
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6e7d01 |
@@ -535,6 +535,38 @@ static int lo_fd(fuse_req_t req, fuse_ino_t ino)
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6e7d01 |
return fd;
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6e7d01 |
}
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6e7d01 |
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6e7d01 |
+/*
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6e7d01 |
+ * Open a file descriptor for an inode. Returns -EBADF if the inode is not a
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6e7d01 |
+ * regular file or a directory.
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6e7d01 |
+ *
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6e7d01 |
+ * Use this helper function instead of raw openat(2) to prevent security issues
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6e7d01 |
+ * when a malicious client opens special files such as block device nodes.
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6e7d01 |
+ * Symlink inodes are also rejected since symlinks must already have been
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6e7d01 |
+ * traversed on the client side.
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6e7d01 |
+ */
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6e7d01 |
+static int lo_inode_open(struct lo_data *lo, struct lo_inode *inode,
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6e7d01 |
+ int open_flags)
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6e7d01 |
+{
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6e7d01 |
+ g_autofree char *fd_str = g_strdup_printf("%d", inode->fd);
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6e7d01 |
+ int fd;
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6e7d01 |
+
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6e7d01 |
+ if (!S_ISREG(inode->filetype) && !S_ISDIR(inode->filetype)) {
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6e7d01 |
+ return -EBADF;
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6e7d01 |
+ }
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6e7d01 |
+
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6e7d01 |
+ /*
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6e7d01 |
+ * The file is a symlink so O_NOFOLLOW must be ignored. We checked earlier
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6e7d01 |
+ * that the inode is not a special file but if an external process races
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6e7d01 |
+ * with us then symlinks are traversed here. It is not possible to escape
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6e7d01 |
+ * the shared directory since it is mounted as "/" though.
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6e7d01 |
+ */
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6e7d01 |
+ fd = openat(lo->proc_self_fd, fd_str, open_flags & ~O_NOFOLLOW);
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6e7d01 |
+ if (fd < 0) {
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6e7d01 |
+ return -errno;
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6e7d01 |
+ }
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6e7d01 |
+ return fd;
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6e7d01 |
+}
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6e7d01 |
+
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6e7d01 |
static void lo_init(void *userdata, struct fuse_conn_info *conn)
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6e7d01 |
{
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6e7d01 |
struct lo_data *lo = (struct lo_data *)userdata;
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6e7d01 |
@@ -788,9 +820,9 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,
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6e7d01 |
if (fi) {
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6e7d01 |
truncfd = fd;
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6e7d01 |
} else {
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6e7d01 |
- sprintf(procname, "%i", ifd);
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6e7d01 |
- truncfd = openat(lo->proc_self_fd, procname, O_RDWR);
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6e7d01 |
+ truncfd = lo_inode_open(lo, inode, O_RDWR);
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|
6e7d01 |
if (truncfd < 0) {
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|
6e7d01 |
+ errno = -truncfd;
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6e7d01 |
goto out_err;
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6e7d01 |
}
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6e7d01 |
}
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6e7d01 |
@@ -894,7 +926,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
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6e7d01 |
struct lo_inode *dir = lo_inode(req, parent);
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6e7d01 |
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6e7d01 |
if (inodep) {
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6e7d01 |
- *inodep = NULL;
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6e7d01 |
+ *inodep = NULL;
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6e7d01 |
}
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6e7d01 |
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6e7d01 |
/*
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6e7d01 |
@@ -1725,19 +1757,26 @@ static void update_open_flags(int writeback, struct fuse_file_info *fi)
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6e7d01 |
fi->flags &= ~O_DIRECT;
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6e7d01 |
}
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6e7d01 |
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6e7d01 |
+/*
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6e7d01 |
+ * Open a regular file, set up an fd mapping, and fill out the struct
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6e7d01 |
+ * fuse_file_info for it. If existing_fd is not negative, use that fd instead
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6e7d01 |
+ * opening a new one. Takes ownership of existing_fd.
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6e7d01 |
+ *
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6e7d01 |
+ * Returns 0 on success or a positive errno.
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6e7d01 |
+ */
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6e7d01 |
static int lo_do_open(struct lo_data *lo, struct lo_inode *inode,
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6e7d01 |
- struct fuse_file_info *fi)
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6e7d01 |
+ int existing_fd, struct fuse_file_info *fi)
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6e7d01 |
{
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6e7d01 |
- char buf[64];
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6e7d01 |
ssize_t fh;
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6e7d01 |
- int fd;
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6e7d01 |
+ int fd = existing_fd;
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6e7d01 |
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6e7d01 |
update_open_flags(lo->writeback, fi);
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6e7d01 |
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6e7d01 |
- sprintf(buf, "%i", inode->fd);
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6e7d01 |
- fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);
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6e7d01 |
- if (fd == -1) {
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|
6e7d01 |
- return errno;
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6e7d01 |
+ if (fd < 0) {
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|
6e7d01 |
+ fd = lo_inode_open(lo, inode, fi->flags);
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6e7d01 |
+ if (fd < 0) {
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|
6e7d01 |
+ return -fd;
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6e7d01 |
+ }
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|
6e7d01 |
}
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|
6e7d01 |
|
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|
6e7d01 |
pthread_mutex_lock(&lo->mutex);
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|
6e7d01 |
@@ -1760,9 +1799,10 @@ static int lo_do_open(struct lo_data *lo, struct lo_inode *inode,
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6e7d01 |
static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
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6e7d01 |
mode_t mode, struct fuse_file_info *fi)
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|
6e7d01 |
{
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|
6e7d01 |
- int fd;
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|
6e7d01 |
+ int fd = -1;
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|
6e7d01 |
struct lo_data *lo = lo_data(req);
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|
6e7d01 |
struct lo_inode *parent_inode;
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|
6e7d01 |
+ struct lo_inode *inode = NULL;
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|
6e7d01 |
struct fuse_entry_param e;
|
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|
6e7d01 |
int err;
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|
6e7d01 |
struct lo_cred old = {};
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|
6e7d01 |
@@ -1788,36 +1828,38 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
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6e7d01 |
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|
6e7d01 |
update_open_flags(lo->writeback, fi);
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|
6e7d01 |
|
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|
6e7d01 |
- fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
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|
6e7d01 |
- mode);
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|
6e7d01 |
+
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|
6e7d01 |
+ fd = openat(parent_inode->fd, name, fi->flags | O_CREAT | O_EXCL, mode);
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|
6e7d01 |
err = fd == -1 ? errno : 0;
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|
6e7d01 |
- lo_restore_cred(&old;;
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6e7d01 |
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|
6e7d01 |
- if (!err) {
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|
6e7d01 |
- ssize_t fh;
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|
6e7d01 |
+ lo_restore_cred(&old;;
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6e7d01 |
|
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|
6e7d01 |
- pthread_mutex_lock(&lo->mutex);
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|
6e7d01 |
- fh = lo_add_fd_mapping(lo, fd);
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|
6e7d01 |
- pthread_mutex_unlock(&lo->mutex);
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|
6e7d01 |
- if (fh == -1) {
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|
6e7d01 |
- close(fd);
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|
6e7d01 |
- err = ENOMEM;
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6e7d01 |
- goto out;
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6e7d01 |
- }
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|
6e7d01 |
+ /* Ignore the error if file exists and O_EXCL was not given */
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6e7d01 |
+ if (err && (err != EEXIST || (fi->flags & O_EXCL))) {
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6e7d01 |
+ goto out;
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6e7d01 |
+ }
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6e7d01 |
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|
6e7d01 |
- fi->fh = fh;
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|
6e7d01 |
- err = lo_do_lookup(req, parent, name, &e, NULL);
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|
6e7d01 |
+ err = lo_do_lookup(req, parent, name, &e, &inode;;
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|
6e7d01 |
+ if (err) {
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6e7d01 |
+ goto out;
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6e7d01 |
}
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|
6e7d01 |
- if (lo->cache == CACHE_NONE) {
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|
6e7d01 |
- fi->direct_io = 1;
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|
6e7d01 |
- } else if (lo->cache == CACHE_ALWAYS) {
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|
6e7d01 |
- fi->keep_cache = 1;
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|
6e7d01 |
+
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|
6e7d01 |
+ err = lo_do_open(lo, inode, fd, fi);
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|
6e7d01 |
+ fd = -1; /* lo_do_open() takes ownership of fd */
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6e7d01 |
+ if (err) {
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|
6e7d01 |
+ /* Undo lo_do_lookup() nlookup ref */
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|
6e7d01 |
+ unref_inode_lolocked(lo, inode, 1);
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|
6e7d01 |
}
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|
6e7d01 |
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6e7d01 |
out:
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|
6e7d01 |
+ lo_inode_put(lo, &inode;;
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|
6e7d01 |
lo_inode_put(lo, &parent_inode);
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|
6e7d01 |
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|
6e7d01 |
if (err) {
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|
6e7d01 |
+ if (fd >= 0) {
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|
6e7d01 |
+ close(fd);
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|
6e7d01 |
+ }
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|
6e7d01 |
+
|
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|
6e7d01 |
fuse_reply_err(req, err);
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|
6e7d01 |
} else {
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|
6e7d01 |
fuse_reply_create(req, &e, fi);
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|
|
6e7d01 |
@@ -1831,7 +1873,6 @@ static struct lo_inode_plock *lookup_create_plock_ctx(struct lo_data *lo,
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|
6e7d01 |
pid_t pid, int *err)
|
|
|
6e7d01 |
{
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|
6e7d01 |
struct lo_inode_plock *plock;
|
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|
6e7d01 |
- char procname[64];
|
|
|
6e7d01 |
int fd;
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|
6e7d01 |
|
|
|
6e7d01 |
plock =
|
|
|
6e7d01 |
@@ -1848,12 +1889,10 @@ static struct lo_inode_plock *lookup_create_plock_ctx(struct lo_data *lo,
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|
6e7d01 |
}
|
|
|
6e7d01 |
|
|
|
6e7d01 |
/* Open another instance of file which can be used for ofd locks. */
|
|
|
6e7d01 |
- sprintf(procname, "%i", inode->fd);
|
|
|
6e7d01 |
-
|
|
|
6e7d01 |
/* TODO: What if file is not writable? */
|
|
|
6e7d01 |
- fd = openat(lo->proc_self_fd, procname, O_RDWR);
|
|
|
6e7d01 |
- if (fd == -1) {
|
|
|
6e7d01 |
- *err = errno;
|
|
|
6e7d01 |
+ fd = lo_inode_open(lo, inode, O_RDWR);
|
|
|
6e7d01 |
+ if (fd < 0) {
|
|
|
6e7d01 |
+ *err = -fd;
|
|
|
6e7d01 |
free(plock);
|
|
|
6e7d01 |
return NULL;
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
@@ -2000,7 +2039,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
|
|
|
6e7d01 |
return;
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
|
|
|
6e7d01 |
- err = lo_do_open(lo, inode, fi);
|
|
|
6e7d01 |
+ err = lo_do_open(lo, inode, -1, fi);
|
|
|
6e7d01 |
lo_inode_put(lo, &inode;;
|
|
|
6e7d01 |
if (err) {
|
|
|
6e7d01 |
fuse_reply_err(req, err);
|
|
|
6e7d01 |
@@ -2056,39 +2095,40 @@ static void lo_flush(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
|
|
|
6e7d01 |
static void lo_fsync(fuse_req_t req, fuse_ino_t ino, int datasync,
|
|
|
6e7d01 |
struct fuse_file_info *fi)
|
|
|
6e7d01 |
{
|
|
|
6e7d01 |
+ struct lo_inode *inode = lo_inode(req, ino);
|
|
|
6e7d01 |
+ struct lo_data *lo = lo_data(req);
|
|
|
6e7d01 |
int res;
|
|
|
6e7d01 |
int fd;
|
|
|
6e7d01 |
- char *buf;
|
|
|
6e7d01 |
|
|
|
6e7d01 |
fuse_log(FUSE_LOG_DEBUG, "lo_fsync(ino=%" PRIu64 ", fi=0x%p)\n", ino,
|
|
|
6e7d01 |
(void *)fi);
|
|
|
6e7d01 |
|
|
|
6e7d01 |
- if (!fi) {
|
|
|
6e7d01 |
- struct lo_data *lo = lo_data(req);
|
|
|
6e7d01 |
-
|
|
|
6e7d01 |
- res = asprintf(&buf, "%i", lo_fd(req, ino));
|
|
|
6e7d01 |
- if (res == -1) {
|
|
|
6e7d01 |
- return (void)fuse_reply_err(req, errno);
|
|
|
6e7d01 |
- }
|
|
|
6e7d01 |
+ if (!inode) {
|
|
|
6e7d01 |
+ fuse_reply_err(req, EBADF);
|
|
|
6e7d01 |
+ return;
|
|
|
6e7d01 |
+ }
|
|
|
6e7d01 |
|
|
|
6e7d01 |
- fd = openat(lo->proc_self_fd, buf, O_RDWR);
|
|
|
6e7d01 |
- free(buf);
|
|
|
6e7d01 |
- if (fd == -1) {
|
|
|
6e7d01 |
- return (void)fuse_reply_err(req, errno);
|
|
|
6e7d01 |
+ if (!fi) {
|
|
|
6e7d01 |
+ fd = lo_inode_open(lo, inode, O_RDWR);
|
|
|
6e7d01 |
+ if (fd < 0) {
|
|
|
6e7d01 |
+ res = -fd;
|
|
|
6e7d01 |
+ goto out;
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
} else {
|
|
|
6e7d01 |
fd = lo_fi_fd(req, fi);
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
|
|
|
6e7d01 |
if (datasync) {
|
|
|
6e7d01 |
- res = fdatasync(fd);
|
|
|
6e7d01 |
+ res = fdatasync(fd) == -1 ? errno : 0;
|
|
|
6e7d01 |
} else {
|
|
|
6e7d01 |
- res = fsync(fd);
|
|
|
6e7d01 |
+ res = fsync(fd) == -1 ? errno : 0;
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
if (!fi) {
|
|
|
6e7d01 |
close(fd);
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
- fuse_reply_err(req, res == -1 ? errno : 0);
|
|
|
6e7d01 |
+out:
|
|
|
6e7d01 |
+ lo_inode_put(lo, &inode;;
|
|
|
6e7d01 |
+ fuse_reply_err(req, res);
|
|
|
6e7d01 |
}
|
|
|
6e7d01 |
|
|
|
6e7d01 |
static void lo_read(fuse_req_t req, fuse_ino_t ino, size_t size, off_t offset,
|
|
|
6e7d01 |
--
|
|
|
6e7d01 |
2.18.2
|
|
|
6e7d01 |
|