Add a way to check if an fd points to the memfd's original open fd
(the one created by memfd_create).
Useful because only the original open fd can be both writable and
executable.
Signed-off-by: Michal Clapinski <mclapinski@xxxxxxxxxx>
---
fs/fcntl.c | 3 +++
include/uapi/linux/fcntl.h | 9 +++++++++
2 files changed, 12 insertions(+)
diff --git a/fs/fcntl.c b/fs/fcntl.c
index e871009f6c88..301527e07a4d 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -419,6 +419,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
case F_SET_RW_HINT:
err = fcntl_rw_hint(filp, cmd, arg);
break;
+ case F_CHECK_ORIGINAL_MEMFD:
+ err = !(filp->f_mode & FMODE_WRITER);
+ break;
default:
break;
}
diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h
index 6c80f96049bd..9a10fe3aafa7 100644
--- a/include/uapi/linux/fcntl.h
+++ b/include/uapi/linux/fcntl.h
@@ -56,6 +56,15 @@
#define F_GET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 13)
#define F_SET_FILE_RW_HINT (F_LINUX_SPECIFIC_BASE + 14)
+/*
+ * Check if the fd points to the memfd's original open fd (the one created by
+ * memfd_create). Returns 1 if yes, 0 if no.
+ * If the fd doesn't point to a memfd, the value should not be interpreted.
+ * Useful because only the original open fd can be both writable and
+ * executable.
+ */
+#define F_CHECK_ORIGINAL_MEMFD (F_LINUX_SPECIFIC_BASE + 15)
+
/*
* Valid hint values for F_{GET,SET}_RW_HINT. 0 is "not set", or can be
* used to clear any hints previously set.
--
2.42.0.283.g2d96d420d3-goog
