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[Qemu-devel] [PULL 28/31] 9pfs: local: mknod: don't follow symlinks
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PULL 28/31] 9pfs: local: mknod: don't follow symlinks |
Date: |
Tue, 28 Feb 2017 00:00:18 +0100 |
The local_mknod() callback is vulnerable to symlink attacks because it
calls:
(1) mknod() which follows symbolic links for all path elements but the
rightmost one
(2) local_set_xattr()->setxattr() which follows symbolic links for all
path elements
(3) local_set_mapped_file_attr() which calls in turn local_fopen() and
mkdir(), both functions following symbolic links for all path
elements but the rightmost one
(4) local_post_create_passthrough() which calls in turn lchown() and
chmod(), both functions also following symbolic links
This patch converts local_mknod() to rely on opendir_nofollow() and
mknodat() to fix (1), as well as local_set_xattrat() and
local_set_mapped_file_attrat() to fix (2) and (3) respectively.
A new local_set_cred_passthrough() helper based on fchownat() and
fchmodat_nofollow() is introduced as a replacement to
local_post_create_passthrough() to fix (4).
The mapped and mapped-file security modes are supposed to be identical,
except for the place where credentials and file modes are stored. While
here, we also make that explicit by sharing the call to mknodat().
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
hw/9pfs/9p-local.c | 68 ++++++++++++++++++++++++++++--------------------------
1 file changed, 35 insertions(+), 33 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index 907ecc59d494..bd95785ff129 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -543,6 +543,23 @@ err:
return -1;
}
+static int local_set_cred_passthrough(FsContext *fs_ctx, int dirfd,
+ const char *name, FsCred *credp)
+{
+ if (fchownat(dirfd, name, credp->fc_uid, credp->fc_gid,
+ AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH) < 0) {
+ /*
+ * If we fail to change ownership and if we are
+ * using security model none. Ignore the error
+ */
+ if ((fs_ctx->export_flags & V9FS_SEC_MASK) != V9FS_SM_NONE) {
+ return -1;
+ }
+ }
+
+ return fchmodat_nofollow(dirfd, name, credp->fc_mode & 07777);
+}
+
static ssize_t local_readlink(FsContext *fs_ctx, V9fsPath *fs_path,
char *buf, size_t bufsz)
{
@@ -736,61 +753,46 @@ out:
static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
const char *name, FsCred *credp)
{
- char *path;
int err = -1;
- int serrno = 0;
- V9fsString fullname;
- char *buffer = NULL;
+ int dirfd;
- v9fs_string_init(&fullname);
- v9fs_string_sprintf(&fullname, "%s/%s", dir_path->data, name);
- path = fullname.data;
+ dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
+ if (dirfd == -1) {
+ return -1;
+ }
- /* Determine the security model */
- if (fs_ctx->export_flags & V9FS_SM_MAPPED) {
- buffer = rpath(fs_ctx, path);
- err = mknod(buffer, SM_LOCAL_MODE_BITS|S_IFREG, 0);
+ if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
+ fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
+ err = mknodat(dirfd, name, SM_LOCAL_MODE_BITS | S_IFREG, 0);
if (err == -1) {
goto out;
}
- err = local_set_xattr(buffer, credp);
- if (err == -1) {
- serrno = errno;
- goto err_end;
- }
- } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
- buffer = rpath(fs_ctx, path);
- err = mknod(buffer, SM_LOCAL_MODE_BITS|S_IFREG, 0);
- if (err == -1) {
- goto out;
+ if (fs_ctx->export_flags & V9FS_SM_MAPPED) {
+ err = local_set_xattrat(dirfd, name, credp);
+ } else {
+ err = local_set_mapped_file_attrat(dirfd, name, credp);
}
- err = local_set_mapped_file_attr(fs_ctx, path, credp);
if (err == -1) {
- serrno = errno;
goto err_end;
}
- } else if ((fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||
- (fs_ctx->export_flags & V9FS_SM_NONE)) {
- buffer = rpath(fs_ctx, path);
- err = mknod(buffer, credp->fc_mode, credp->fc_rdev);
+ } else if (fs_ctx->export_flags & V9FS_SM_PASSTHROUGH ||
+ fs_ctx->export_flags & V9FS_SM_NONE) {
+ err = mknodat(dirfd, name, credp->fc_mode, credp->fc_rdev);
if (err == -1) {
goto out;
}
- err = local_post_create_passthrough(fs_ctx, path, credp);
+ err = local_set_cred_passthrough(fs_ctx, dirfd, name, credp);
if (err == -1) {
- serrno = errno;
goto err_end;
}
}
goto out;
err_end:
- remove(buffer);
- errno = serrno;
+ unlinkat_preserve_errno(dirfd, name, 0);
out:
- g_free(buffer);
- v9fs_string_free(&fullname);
+ close_preserve_errno(dirfd);
return err;
}
--
2.7.4
- [Qemu-devel] [PULL 19/31] 9pfs: local: readlink: don't follow symlinks, (continued)
- [Qemu-devel] [PULL 19/31] 9pfs: local: readlink: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 20/31] 9pfs: local: lstat: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 23/31] 9pfs: local: improve error handling in link op, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 26/31] 9pfs: local: chown: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 18/31] 9pfs: local: truncate: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 22/31] 9pfs: local: rename: use renameat, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 09/31] 9pfs: local: open/opendir: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 30/31] 9pfs: local: open2: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 29/31] 9pfs: local: mkdir: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 31/31] 9pfs: local: drop unused code, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 28/31] 9pfs: local: mknod: don't follow symlinks,
Greg Kurz <=
- [Qemu-devel] [PULL 24/31] 9pfs: local: link: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 27/31] 9pfs: local: symlink: don't follow symlinks, Greg Kurz, 2017/02/27
- [Qemu-devel] [PULL 25/31] 9pfs: local: chmod: don't follow symlinks, Greg Kurz, 2017/02/27
- Re: [Qemu-devel] [PULL 00/31] 9p patches 2017-02-27 for 2.9 soft freeze, no-reply, 2017/02/27
- Re: [Qemu-devel] [PULL 00/31] 9p patches 2017-02-27 for 2.9 soft freeze, no-reply, 2017/02/27
- Re: [Qemu-devel] [PULL 00/31] 9p patches 2017-02-27 for 2.9 soft freeze, Greg Kurz, 2017/02/27