[Qemu-devel] [PATCH 10/29] 9pfs: local: lsetxattr: don't follow symlinks

[Greg Kurz]

The local_lsetxattr() callback is vulnerable to symlink attacks because
it calls lsetxattr() which follows symbolic links in all path elements but
the rightmost one.

This patch converts local_lsetxattr() to rely on opendir_nofollow() and
fsetxattrat_nofollow() instead.

This partly fixes CVE-2016-9602.

Signed-off-by: Greg Kurz <gr...@kaod.org>
---
 hw/9pfs/9p-posix-acl.c  |   18 ++++--------------
 hw/9pfs/9p-xattr-user.c |    8 +-------
 hw/9pfs/9p-xattr.c      |    8 +-------
 3 files changed, 6 insertions(+), 28 deletions(-)

diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c
index 9435e27a368c..0154e2a7605f 100644
--- a/hw/9pfs/9p-posix-acl.c
+++ b/hw/9pfs/9p-posix-acl.c
@@ -50,13 +50,8 @@ static ssize_t mp_pacl_listxattr(FsContext *ctx, const char 
*path,
 static int mp_pacl_setxattr(FsContext *ctx, const char *path, const char *name,
                             void *value, size_t size, int flags)
 {
-    char *buffer;
-    int ret;
-
-    buffer = rpath(ctx, path);
-    ret = lsetxattr(buffer, MAP_ACL_ACCESS, value, size, flags);
-    g_free(buffer);
-    return ret;
+    return local_setxattr_nofollow(ctx, path, MAP_ACL_ACCESS, value, size,
+                                   flags);
 }
 
 static int mp_pacl_removexattr(FsContext *ctx,
@@ -108,13 +103,8 @@ static ssize_t mp_dacl_listxattr(FsContext *ctx, const 
char *path,
 static int mp_dacl_setxattr(FsContext *ctx, const char *path, const char *name,
                             void *value, size_t size, int flags)
 {
-    char *buffer;
-    int ret;
-
-    buffer = rpath(ctx, path);
-    ret = lsetxattr(buffer, MAP_ACL_DEFAULT, value, size, flags);
-    g_free(buffer);
-    return ret;
+    return local_setxattr_nofollow(ctx, path, MAP_ACL_DEFAULT, value, size,
+                                   flags);
 }
 
 static int mp_dacl_removexattr(FsContext *ctx,
diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c
index 4071fbc4c086..1840a5db66f3 100644
--- a/hw/9pfs/9p-xattr-user.c
+++ b/hw/9pfs/9p-xattr-user.c
@@ -67,9 +67,6 @@ static ssize_t mp_user_listxattr(FsContext *ctx, const char 
*path,
 static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name,
                             void *value, size_t size, int flags)
 {
-    char *buffer;
-    int ret;
-
     if (strncmp(name, "user.virtfs.", 12) == 0) {
         /*
          * Don't allow fetch of user.virtfs namesapce
@@ -78,10 +75,7 @@ static int mp_user_setxattr(FsContext *ctx, const char 
*path, const char *name,
         errno = EACCES;
         return -1;
     }
-    buffer = rpath(ctx, path);
-    ret = lsetxattr(buffer, name, value, size, flags);
-    g_free(buffer);
-    return ret;
+    return local_setxattr_nofollow(ctx, path, name, value, size, flags);
 }
 
 static int mp_user_removexattr(FsContext *ctx,
diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c
index 803d4bbbc50b..72ef820f16d7 100644
--- a/hw/9pfs/9p-xattr.c
+++ b/hw/9pfs/9p-xattr.c
@@ -328,13 +328,7 @@ ssize_t pt_getxattr(FsContext *ctx, const char *path, 
const char *name,
 int pt_setxattr(FsContext *ctx, const char *path, const char *name, void 
*value,
                 size_t size, int flags)
 {
-    char *buffer;
-    int ret;
-
-    buffer = rpath(ctx, path);
-    ret = lsetxattr(buffer, name, value, size, flags);
-    g_free(buffer);
-    return ret;
+    return local_setxattr_nofollow(ctx, path, name, value, size, flags);
 }
 
 int pt_removexattr(FsContext *ctx, const char *path, const char *name)