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@google.com --- 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.