File 0197-9pfs-local-set-the-path-of-the-expo.patch of Package qemu-linux-user.29142

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File 0197-9pfs-local-set-the-path-of-the-expo.patch of Package qemu-linux-user.29142

From: Greg Kurz <groug@kaod.org>
Date: Mon, 17 Apr 2017 10:53:23 +0200
Subject: 9pfs: local: set the path of the export root to "."
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The local backend was recently converted to using "at*()" syscalls in order
to ensure all accesses happen below the shared directory. This requires that
we only pass relative paths, otherwise the dirfd argument to the "at*()"
syscalls is ignored and the path is treated as an absolute path in the host.
This is actually the case for paths in all fids, with the notable exception
of the root fid, whose path is "/". This causes the following backend ops to
act on the "/" directory of the host instead of the virtfs shared directory
when the export root is involved:
- lstat
- chmod
- chown
- utimensat

ie, chmod /9p_mount_point in the guest will be converted to chmod / in the
host for example. This could cause security issues with a privileged QEMU.

All "*at()" syscalls are being passed an open file descriptor. In the case
of the export root, this file descriptor points to the path in the host that
was passed to -fsdev.

The fix is thus as simple as changing the path of the export root fid to be
"." instead of "/".

This is CVE-2017-7471.

Cc: qemu-stable@nongnu.org
Reported-by: Léo Gaspard <leo@gaspard.io>
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 9c6b899f7a46893ab3b671e341a2234e9c0c060e)
[BR: BSC#1034866 CVE-2017-7471]
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 hw/9pfs/9p-local.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index ef24c1b3eb2a15bb5f9e75536e7a..e93d48edabc8ac45eba0a35e6dd0 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -1097,8 +1097,13 @@ static int local_name_to_path(FsContext *ctx, V9fsPath *dir_path,
 {
     if (dir_path) {
         v9fs_path_sprintf(target, "%s/%s", dir_path->data, name);
-    } else {
+    } else if (strcmp(name, "/")) {
         v9fs_path_sprintf(target, "%s", name);
+    } else {
+        /* We want the path of the export root to be relative, otherwise
+         * "*at()" syscalls would treat it as "/" in the host.
+         */
+        v9fs_path_sprintf(target, "%s", ".");
     }
     return 0;
 }

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File 0197-9pfs-local-set-the-path-of-the-expo.patch of Package qemu-linux-user.29142

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