[CRIU] [PATCH] exec: Don't open code get_close_on_exec

[Eric W. Biederman]

Al Viro pointed out that moving unshare_files makes the close_on_exec
test in bprm_exec unsafe because the rcu_read_lock is not held[1].

Fix this by using the helper get_close_on_exec, which is safe in the
presence of a shared files_struct.

[1] https://lkml.kernel.org/r/20201207222214.GA4115853@ZenIV.linux.org.uk
Fixes: 030a5fcfda42 ("exec: Move unshare_files to fix posix file locking during exec")
Suggested-by: Al Viro <viro at ftp.linux.org.uk>
Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
---
 fs/exec.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 9e9368603168..9917ebcd0fe5 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1812,8 +1812,7 @@ static int bprm_execve(struct linux_binprm *bprm,
 	 * than having the interpreter start and then immediately fail
 	 * when it finds the executable is inaccessible.
 	 */
-	if (bprm->fdpath &&
-	    close_on_exec(fd, rcu_dereference_raw(current->files->fdt)))
+	if (bprm->fdpath && get_close_on_exec(fd))
 		bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE;
 
 	/* Set the unchanging part of bprm->cred */
-- 
2.20.1