[Qemu-stable] [PATCH 34/81] 9pfs: fix vulnerability in openat_dir() and local_unlinkat_common()

[Michael Roth]

From: Greg Kurz <address@hidden>

We should pass O_NOFOLLOW otherwise openat() will follow symlinks and make
QEMU vulnerable.

While here, we also fix local_unlinkat_common() to use openat_dir() for
the same reasons (it was a leftover in the original patchset actually).

This fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Daniel P. Berrange <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
(cherry picked from commit b003fc0d8aa5e7060dbf7e5862b8013c73857c7f)
Signed-off-by: Greg Kurz <address@hidden>
Signed-off-by: Michael Roth <address@hidden>
---
 hw/9pfs/9p-local.c | 2 +-
 hw/9pfs/9p-util.h  | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index f282bb7..227de61 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -961,7 +961,7 @@ static int local_unlinkat_common(FsContext *ctx, int dirfd, 
const char *name,
         if (flags == AT_REMOVEDIR) {
             int fd;
 
-            fd = openat(dirfd, name, O_RDONLY | O_DIRECTORY | O_PATH);
+            fd = openat_dir(dirfd, name);
             if (fd == -1) {
                 goto err_out;
             }
diff --git a/hw/9pfs/9p-util.h b/hw/9pfs/9p-util.h
index cb7b207..517027c 100644
--- a/hw/9pfs/9p-util.h
+++ b/hw/9pfs/9p-util.h
@@ -27,7 +27,8 @@ static inline int openat_dir(int dirfd, const char *name)
 #else
 #define OPENAT_DIR_O_PATH 0
 #endif
-    return openat(dirfd, name, O_DIRECTORY | O_RDONLY | OPENAT_DIR_O_PATH);
+    return openat(dirfd, name,
+                  O_DIRECTORY | O_RDONLY | O_NOFOLLOW | OPENAT_DIR_O_PATH);
 }
 
 static inline int openat_file(int dirfd, const char *name, int flags,
-- 
2.7.4