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[Qemu-devel] [PATCH 24/29] 9pfs: local: chown: don't follow symlinks
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PATCH 24/29] 9pfs: local: chown: don't follow symlinks |
Date: |
Mon, 20 Feb 2017 15:42:26 +0100 |
User-agent: |
StGit/0.17.1-20-gc0b1b-dirty |
The local_chown() callback is vulnerable to symlink attacks because it
calls:
(1) lchown() 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
This patch converts local_chown() to rely on open_nofollow() and
fchownat() to fix (1), as well as local_set_xattrat() and
local_set_mapped_file_attrat() to fix (2) and (3) respectively.
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
---
hw/9pfs/9p-local.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index 56d7731f7ce1..7f1e105d72aa 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -1138,23 +1138,31 @@ static int local_truncate(FsContext *ctx, V9fsPath
*fs_path, off_t size)
static int local_chown(FsContext *fs_ctx, V9fsPath *fs_path, FsCred *credp)
{
- char *buffer;
+ char *dirpath = g_path_get_dirname(fs_path->data);
+ char *name = g_path_get_basename(fs_path->data);
int ret = -1;
- char *path = fs_path->data;
+ int dirfd;
+
+ dirfd = local_opendir_nofollow(fs_ctx, dirpath);
+ if (dirfd == -1) {
+ goto out;
+ }
if ((credp->fc_uid == -1 && credp->fc_gid == -1) ||
(fs_ctx->export_flags & V9FS_SM_PASSTHROUGH) ||
(fs_ctx->export_flags & V9FS_SM_NONE)) {
- buffer = rpath(fs_ctx, path);
- ret = lchown(buffer, credp->fc_uid, credp->fc_gid);
- g_free(buffer);
+ ret = fchownat(dirfd, name, credp->fc_uid, credp->fc_gid,
+ AT_SYMLINK_NOFOLLOW);
} else if (fs_ctx->export_flags & V9FS_SM_MAPPED) {
- buffer = rpath(fs_ctx, path);
- ret = local_set_xattr(buffer, credp);
- g_free(buffer);
+ ret = local_set_xattrat(dirfd, name, credp);
} else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
- return local_set_mapped_file_attr(fs_ctx, path, credp);
+ ret = local_set_mapped_file_attrat(dirfd, name, credp);
}
+
+ close_preserve_errno(dirfd);
+out:
+ g_free(name);
+ g_free(dirpath);
return ret;
}
- [Qemu-devel] [PATCH 21/29] 9pfs: local: improve error handling in link op, (continued)
[Qemu-devel] [PATCH 24/29] 9pfs: local: chown: don't follow symlinks,
Greg Kurz <=
[Qemu-devel] [PATCH 25/29] 9pfs: local: symlink: don't follow symlinks, Greg Kurz, 2017/02/20
[Qemu-devel] [PATCH 26/29] 9pfs: local: mknod: don't follow symlinks, Greg Kurz, 2017/02/20
[Qemu-devel] [PATCH 27/29] 9pfs: local: mkdir: don't follow symlinks, Greg Kurz, 2017/02/20
[Qemu-devel] [PATCH 28/29] 9pfs: local: open2: don't follow symlinks, Greg Kurz, 2017/02/20
[Qemu-devel] [PATCH 29/29] 9pfs: local: drop unused code, Greg Kurz, 2017/02/20