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authorJeff Xu <jeffxu@google.com>2022-12-15 00:12:04 +0000
committerAndrew Morton <akpm@linux-foundation.org>2023-01-18 17:12:37 -0800
commitc4f75bc8bd6b3d62665e1f5400c419540edb5601 (patch)
tree4eadb91f046f0e270ff092286b6c806c4e1b17d0
parent105ff5339f498af74e60d7662c8f1c4d21f1342d (diff)
mm/memfd: add write seals when apply SEAL_EXEC to executable memfd
In order to avoid WX mappings, add F_SEAL_WRITE when apply F_SEAL_EXEC to an executable memfd, so W^X from start. This implys application need to fill the content of the memfd first, after F_SEAL_EXEC is applied, application can no longer modify the content of the memfd. Typically, application seals the memfd right after writing to it. For example: 1. memfd_create(MFD_EXEC). 2. write() code to the memfd. 3. fcntl(F_ADD_SEALS, F_SEAL_EXEC) to convert the memfd to W^X. 4. call exec() on the memfd. Link: https://lkml.kernel.org/r/20221215001205.51969-5-jeffxu@google.com Signed-off-by: Jeff Xu <jeffxu@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Cc: Daniel Verkamp <dverkamp@chromium.org> Cc: David Herrmann <dh.herrmann@gmail.com> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jann Horn <jannh@google.com> Cc: Jorge Lucangeli Obes <jorgelo@chromium.org> Cc: kernel test robot <lkp@intel.com> Cc: Shuah Khan <skhan@linuxfoundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--mm/memfd.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/memfd.c b/mm/memfd.c
index bc214390e28d..a0a7a37e8177 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -222,6 +222,12 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
}
}
+ /*
+ * SEAL_EXEC implys SEAL_WRITE, making W^X from the start.
+ */
+ if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
+ seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE;
+
*file_seals |= seals;
error = 0;