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[PULL,15/28] 9pfs: local: truncate: don't follow symlinks

Message ID 1488277840-18608-16-git-send-email-groug@kaod.org
State New
Headers show

Commit Message

Greg Kurz Feb. 28, 2017, 10:30 a.m. UTC 
The local_truncate() callback is vulnerable to symlink attacks because
it calls truncate() which follows symbolic links in all path elements.

This patch converts local_truncate() to rely on open_nofollow() and
ftruncate() instead.

This partly fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/9pfs/9p-local.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)
diff mbox

Patch

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index 95b2c1c34172..1a3dfd774012 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -894,13 +894,14 @@  err_out:
 
 static int local_truncate(FsContext *ctx, V9fsPath *fs_path, off_t size)
 {
-    char *buffer;
-    int ret;
-    char *path = fs_path->data;
+    int fd, ret;
 
-    buffer = rpath(ctx, path);
-    ret = truncate(buffer, size);
-    g_free(buffer);
+    fd = local_open_nofollow(ctx, fs_path->data, O_WRONLY, 0);
+    if (fd == -1) {
+        return -1;
+    }
+    ret = ftruncate(fd, size);
+    close_preserve_errno(fd);
     return ret;
 }