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[Qemu-devel] [PATCH v2 08/28] 9pfs: local: llistxattr: don't follow syml
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PATCH v2 08/28] 9pfs: local: llistxattr: don't follow symlinks |
Date: |
Sun, 26 Feb 2017 23:42:34 +0100 |
User-agent: |
StGit/0.17.1-20-gc0b1b-dirty |
The local_llistxattr() callback is vulnerable to symlink attacks because
it calls llistxattr() which follows symbolic links in all path elements but
the rightmost one.
This patch introduces a helper to emulate the non-existing flistxattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to llistxattr().
local_llistxattr() is converted to use this helper and opendir_nofollow().
This partly fixes CVE-2016-9602.
Signed-off-by: Greg Kurz <address@hidden>
---
v2: - introduce /proc based flistxattrat_nofollow()
---
hw/9pfs/9p-xattr.c | 35 +++++++++++++++++++++++++++++------
1 file changed, 29 insertions(+), 6 deletions(-)
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index aa4391e6b317..54193c630c9d 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -60,6 +60,16 @@ ssize_t pt_listxattr(FsContext *ctx, const char *path,
return name_size;
}
+static ssize_t flistxattrat_nofollow(int dirfd, const char *filename,
+ char *list, size_t size)
+{
+ char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename);
+ int ret;
+
+ ret = llistxattr(proc_path, list, size);
+ g_free(proc_path);
+ return ret;
+}
/*
* Get the list and pass to each layer to find out whether
@@ -69,24 +79,37 @@ ssize_t v9fs_list_xattr(FsContext *ctx, const char *path,
void *value, size_t vsize)
{
ssize_t size = 0;
- char *buffer;
void *ovalue = value;
XattrOperations *xops;
char *orig_value, *orig_value_start;
ssize_t xattr_len, parsed_len = 0, attr_len;
+ char *dirpath, *name;
+ int dirfd;
/* Get the actual len */
- buffer = rpath(ctx, path);
- xattr_len = llistxattr(buffer, value, 0);
+ dirpath = g_path_get_dirname(path);
+ dirfd = local_opendir_nofollow(ctx, dirpath);
+ g_free(dirpath);
+ if (dirfd == -1) {
+ return -1;
+ }
+
+ name = g_path_get_basename(path);
+ xattr_len = flistxattrat_nofollow(dirfd, name, value, 0);
if (xattr_len <= 0) {
- g_free(buffer);
+ g_free(name);
+ close_preserve_errno(dirfd);
return xattr_len;
}
/* Now fetch the xattr and find the actual size */
orig_value = g_malloc(xattr_len);
- xattr_len = llistxattr(buffer, orig_value, xattr_len);
- g_free(buffer);
+ xattr_len = flistxattrat_nofollow(dirfd, name, orig_value, xattr_len);
+ g_free(name);
+ close_preserve_errno(dirfd);
+ if (xattr_len < 0) {
+ return -1;
+ }
/* store the orig pointer */
orig_value_start = orig_value;
- [Qemu-devel] [PATCH v2 01/28] 9pfs: local: move xattr security ops to 9p-xattr.c, (continued)
- [Qemu-devel] [PATCH v2 01/28] 9pfs: local: move xattr security ops to 9p-xattr.c, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 02/28] 9pfs: remove side-effects in local_init(), Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 03/28] 9pfs: remove side-effects in local_open() and local_opendir(), Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 04/28] 9pfs: introduce openat_nofollow() helper, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 05/28] 9pfs: local: keep a file descriptor on the shared folder, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 06/28] 9pfs: local: open/opendir: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 07/28] 9pfs: local: lgetxattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 08/28] 9pfs: local: llistxattr: don't follow symlinks,
Greg Kurz <=
- [Qemu-devel] [PATCH v2 09/28] 9pfs: local: lsetxattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 10/28] 9pfs: local: lremovexattr: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 11/28] 9pfs: local: unlinkat: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 12/28] 9pfs: local: remove: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 13/28] 9pfs: local: utimensat: don't follow symlinks, Greg Kurz, 2017/02/26
- [Qemu-devel] [PATCH v2 14/28] 9pfs: local: statfs: don't follow symlinks, Greg Kurz, 2017/02/26