Merge tag 'fs.openat2.unknown_flags.v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull openat2 fixes from Christian Brauner:

 - Remove the unused VALID_UPGRADE_FLAGS define we carried from an
   extension to openat2() that we haven't merged. Aleksa might be
   getting back to it at some point but just not right now.

 - openat2() used to accidently ignore unknown flag values in the upper
   32 bits.

   The new openat2() syscall verifies that no unknown O-flag values are
   set and returns an error to userspace if they are while the older
   open syscalls like open() and openat() simply ignore unknown flag
   values:

      #define O_FLAG_CURRENTLY_INVALID (1 << 31)
      struct open_how how = {
            .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID,
            .resolve = 0,
      };

      /* fails */
      fd = openat2(-EBADF, "/dev/null", &how, sizeof(how));

      /* succeeds */
      fd = openat(-EBADF, "/dev/null", O_RDONLY | O_FLAG_CURRENTLY_INVALID);

   However, openat2() silently truncates the upper 32 bits meaning:

      #define O_FLAG_CURRENTLY_INVALID_LOWER32 (1 << 31)
      #define O_FLAG_CURRENTLY_INVALID_UPPER32 (1 << 40)

      struct open_how how_lowe32 = {
            .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_LOWER32,
      };

      struct open_how how_upper32 = {
            .flags = O_RDONLY | O_FLAG_CURRENTLY_INVALID_UPPER32,
      };

      /* fails */
      fd = openat2(-EBADF, "/dev/null", &how_lower32, sizeof(how_lower32));

      /* succeeds */
      fd = openat2(-EBADF, "/dev/null", &how_upper32, sizeof(how_upper32));

   Fix this by preventing the immediate truncation in build_open_flags()
   and add a compile-time check to catch when we add flags in the upper
   32 bit range.

* tag 'fs.openat2.unknown_flags.v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  test: add openat2() test for invalid upper 32 bit flag value
  open: don't silently ignore unknown O-flags in openat2()
  fcntl: remove unused VALID_UPGRADE_FLAGS

1 files changed, 11 insertions, 3 deletions

diff --git a/fs/open.c b/fs/open.c
index e53af13b5835..53bc0573c0ec 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1002,12 +1002,20 @@ inline struct open_how build_open_how(int flags, umode_t mode)
 
 inline int build_open_flags(const struct open_how *how, struct open_flags *op)
 {
-	int flags = how->flags;
+	u64 flags = how->flags;
+	u64 strip = FMODE_NONOTIFY | O_CLOEXEC;
 	int lookup_flags = 0;
 	int acc_mode = ACC_MODE(flags);
 
-	/* Must never be set by userspace */
-	flags &= ~(FMODE_NONOTIFY | O_CLOEXEC);
+	BUILD_BUG_ON_MSG(upper_32_bits(VALID_OPEN_FLAGS),
+			 "struct open_flags doesn't yet handle flags > 32 bits");
+
+	/*
+	 * Strip flags that either shouldn't be set by userspace like
+	 * FMODE_NONOTIFY or that aren't relevant in determining struct
+	 * open_flags like O_CLOEXEC.
+	 */
+	flags &= ~strip;
 
 	/*
 	 * Older syscalls implicitly clear all of the invalid flags or argument