gnu: qemu: Fix CVE-2017-7493.

* gnu/packages/patches/qemu-CVE-2017-7493.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/qemu.scm (qemu)[source]: Use it.

2 files changed, 183 insertions, 0 deletions

diff --git a/gnu/packages/patches/qemu-CVE-2017-7493.patch b/gnu/packages/patches/qemu-CVE-2017-7493.patch
new file mode 100644
index 0000000000..67b26fad81
--- /dev/null
+++ b/gnu/packages/patches/qemu-CVE-2017-7493.patch
@@ -0,0 +1,182 @@
+Fix CVE-2017-7493:
+
+https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-7493
+
+Patch copied from upstream source repository:
+
+http://git.qemu.org/?p=qemu.git;a=commit;h=7a95434e0ca8a037fd8aa1a2e2461f92585eb77b
+
+From 7a95434e0ca8a037fd8aa1a2e2461f92585eb77b Mon Sep 17 00:00:00 2001
+From: Greg Kurz <groug@kaod.org>
+Date: Fri, 5 May 2017 14:48:08 +0200
+Subject: [PATCH] 9pfs: local: forbid client access to metadata (CVE-2017-7493)
+
+When using the mapped-file security mode, we shouldn't let the client mess
+with the metadata. The current code already tries to hide the metadata dir
+from the client by skipping it in local_readdir(). But the client can still
+access or modify it through several other operations. This can be used to
+escalate privileges in the guest.
+
+Affected backend operations are:
+- local_mknod()
+- local_mkdir()
+- local_open2()
+- local_symlink()
+- local_link()
+- local_unlinkat()
+- local_renameat()
+- local_rename()
+- local_name_to_path()
+
+Other operations are safe because they are only passed a fid path, which
+is computed internally in local_name_to_path().
+
+This patch converts all the functions listed above to fail and return
+EINVAL when being passed the name of the metadata dir. This may look
+like a poor choice for errno, but there's no such thing as an illegal
+path name on Linux and I could not think of anything better.
+
+This fixes CVE-2017-7493.
+
+Reported-by: Leo Gaspard <leo@gaspard.io>
+Signed-off-by: Greg Kurz <groug@kaod.org>
+Reviewed-by: Eric Blake <eblake@redhat.com>
+---
+ hw/9pfs/9p-local.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
+ 1 file changed, 56 insertions(+), 2 deletions(-)
+
+diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
+index f3ebca4f7a..a2486566af 100644
+--- a/hw/9pfs/9p-local.c
++++ b/hw/9pfs/9p-local.c
+@@ -452,6 +452,11 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState *fs)
+     return telldir(fs->dir.stream);
+ }
+ 
++static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name)
++{
++    return !strcmp(name, VIRTFS_META_DIR);
++}
++
+ static struct dirent *local_readdir(FsContext *ctx, V9fsFidOpenState *fs)
+ {
+     struct dirent *entry;
+@@ -465,8 +470,8 @@ again:
+     if (ctx->export_flags & V9FS_SM_MAPPED) {
+         entry->d_type = DT_UNKNOWN;
+     } else if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
+-        if (!strcmp(entry->d_name, VIRTFS_META_DIR)) {
+-            /* skp the meta data directory */
++        if (local_is_mapped_file_metadata(ctx, entry->d_name)) {
++            /* skip the meta data directory */
+             goto again;
+         }
+         entry->d_type = DT_UNKNOWN;
+@@ -559,6 +564,12 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
+     int err = -1;
+     int dirfd;
+ 
++    if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(fs_ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
+     if (dirfd == -1) {
+         return -1;
+@@ -605,6 +616,12 @@ static int local_mkdir(FsContext *fs_ctx, V9fsPath *dir_path,
+     int err = -1;
+     int dirfd;
+ 
++    if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(fs_ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
+     if (dirfd == -1) {
+         return -1;
+@@ -694,6 +711,12 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
+     int err = -1;
+     int dirfd;
+ 
++    if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(fs_ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     /*
+      * Mark all the open to not follow symlinks
+      */
+@@ -752,6 +775,12 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath,
+     int err = -1;
+     int dirfd;
+ 
++    if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(fs_ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     dirfd = local_opendir_nofollow(fs_ctx, dir_path->data);
+     if (dirfd == -1) {
+         return -1;
+@@ -826,6 +855,12 @@ static int local_link(FsContext *ctx, V9fsPath *oldpath,
+     int ret = -1;
+     int odirfd, ndirfd;
+ 
++    if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     odirfd = local_opendir_nofollow(ctx, odirpath);
+     if (odirfd == -1) {
+         goto out;
+@@ -1096,6 +1131,12 @@ static int local_lremovexattr(FsContext *ctx, V9fsPath *fs_path,
+ static int local_name_to_path(FsContext *ctx, V9fsPath *dir_path,
+                               const char *name, V9fsPath *target)
+ {
++    if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     if (dir_path) {
+         v9fs_path_sprintf(target, "%s/%s", dir_path->data, name);
+     } else if (strcmp(name, "/")) {
+@@ -1116,6 +1157,13 @@ static int local_renameat(FsContext *ctx, V9fsPath *olddir,
+     int ret;
+     int odirfd, ndirfd;
+ 
++    if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        (local_is_mapped_file_metadata(ctx, old_name) ||
++         local_is_mapped_file_metadata(ctx, new_name))) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     odirfd = local_opendir_nofollow(ctx, olddir->data);
+     if (odirfd == -1) {
+         return -1;
+@@ -1206,6 +1254,12 @@ static int local_unlinkat(FsContext *ctx, V9fsPath *dir,
+     int ret;
+     int dirfd;
+ 
++    if (ctx->export_flags & V9FS_SM_MAPPED_FILE &&
++        local_is_mapped_file_metadata(ctx, name)) {
++        errno = EINVAL;
++        return -1;
++    }
++
+     dirfd = local_opendir_nofollow(ctx, dir->data);
+     if (dirfd == -1) {
+         return -1;
+-- 
+2.13.0
+
diff --git a/gnu/packages/qemu.scm b/gnu/packages/qemu.scm
index 30b9908aa0..0734b6d0f7 100644
--- a/gnu/packages/qemu.scm
+++ b/gnu/packages/qemu.scm
@@ -74,6 +74,7 @@
              (method url-fetch)
              (uri (string-append "http://wiki.qemu-project.org/download/qemu-"
                                  version ".tar.xz"))
+             (patches (search-patches "qemu-CVE-2017-7493.patch"))
              (sha256
               (base32
                "08mhfs0ndbkyqgw7fjaa9vjxf4dinrly656f6hjzvmaz7hzc677h"))))