pipe(2) - race-free error recovery

don't mess with sys_close() if copy_to_user() fails; just postpone
fd_install() until we know it hasn't.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 22 insertions, 9 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 8d85d7068c1e..bd3479db4b62 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1064,9 +1064,8 @@ err_inode:
         return err;
 }
 
-int do_pipe_flags(int *fd, int flags)
+static int __do_pipe_flags(int *fd, struct file **files, int flags)
 {
-        struct file *files[2];
         int error;
         int fdw, fdr;
 
@@ -1088,11 +1087,8 @@ int do_pipe_flags(int *fd, int flags)
         fdw = error;
 
         audit_fd_pair(fdr, fdw);
-        fd_install(fdr, files[0]);
-        fd_install(fdw, files[1]);
         fd[0] = fdr;
         fd[1] = fdw;
-
         return 0;
 
  err_fdr:
@@ -1103,21 +1099,38 @@ int do_pipe_flags(int *fd, int flags)
         return error;
 }
 
+int do_pipe_flags(int *fd, int flags)
+{
+        struct file *files[2];
+        int error = __do_pipe_flags(fd, files, flags);
+        if (!error) {
+                fd_install(fd[0], files[0]);
+                fd_install(fd[1], files[1]);
+        }
+        return error;
+}
+
 /*
  * sys_pipe() is the normal C calling standard for creating
  * a pipe. It's not the way Unix traditionally does this, though.
  */
 SYSCALL_DEFINE2(pipe2, int __user *, fildes, int, flags)
 {
+        struct file *files[2];
         int fd[2];
         int error;
 
-        error = do_pipe_flags(fd, flags);
+        error = __do_pipe_flags(fd, files, flags);
         if (!error) {
-                if (copy_to_user(fildes, fd, sizeof(fd))) {
-                        sys_close(fd[0]);
-                        sys_close(fd[1]);
+                if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
+                        fput(files[0]);
+                        fput(files[1]);
+                        put_unused_fd(fd[0]);
+                        put_unused_fd(fd[1]);
                         error = -EFAULT;
+                } else {
+                        fd_install(fd[0], files[0]);
+                        fd_install(fd[1], files[1]);
                 }
         }
         return error;