linux-kernel - [PATCH 1/4] exec: Pass unshared files_struct to load

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Date:   Thu, 11 Jan 2018 18:50:03 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        jslaby@...e.com, viro@...iv.linux.org.uk, keescook@...omium.org,
        serge@...lyn.com, james.l.morris@...cle.com, luto@...nel.org,
        john.johansen@...onical.com, oleg@...hat.com, mingo@...nel.org,
        akpm@...ux-foundation.org, mhocko@...e.com, peterz@...radead.org,
        ktkhai@...tuozzo.com
Subject: [PATCH 1/4] exec: Pass unshared files_struct to load_binary()

This patch adds pointer to new unshared files_struct to struct linux_binprm
and makes load_misc_binary() method to use __alloc_fd() and __fd_install(),
instead of alloc_fd() and fd_install(), which are related to current task.
It's a preparation for next patch, that stops assigning of current->files
before load_binary call. Since bprm->new_files == current->files now,
this patch is just a preparation, and it don't change functionality.
The only difference is export of two functions, that I pointed above.

load_misc_binary() is the only load_binary method modifying fd table,
so other methods are not modified.

Note, that I don't replace sys_close(fd_binary) with __close_fd()
in load_misc_binary(), because of next patch will kill this close
completely, while __close_fd() requires to be exported too. It's
pointless to export it and then to unexport it, so we skip this.

Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
---
 fs/binfmt_misc.c        |    6 ++++--
 fs/exec.c               |    1 +
 fs/file.c               |    2 ++
 include/linux/binfmts.h |    1 +
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index a7c5a9861bef..13c1fae45717 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -19,6 +19,7 @@
 #include <linux/ctype.h>
 #include <linux/string_helpers.h>
 #include <linux/file.h>
+#include <linux/fdtable.h>
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/mount.h>
@@ -164,12 +165,13 @@ static int load_misc_binary(struct linux_binprm *bprm)
 		 * interpreter than keep it open and assign descriptor
 		 * to it
 		 */
-		fd_binary = get_unused_fd_flags(0);
+		fd_binary = __alloc_fd(bprm->new_files, 0,
+				       rlimit(RLIMIT_NOFILE), 0);
 		if (fd_binary < 0) {
 			retval = fd_binary;
 			goto ret;
 		}
-		fd_install(fd_binary, bprm->file);
+		__fd_install(bprm->new_files, fd_binary, bprm->file);
 
 		/* if the binary is not readable than enforce mm->dumpable=0
 		   regardless of the interpreter's permissions */
diff --git a/fs/exec.c b/fs/exec.c
index 7eb8d21bcab9..4c3b924ae103 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1729,6 +1729,7 @@ static int do_execveat_common(int fd, struct filename *filename,
 	bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
 	if (!bprm)
 		goto out_files;
+	bprm->new_files = current->files;
 
 	retval = prepare_bprm_creds(bprm);
 	if (retval)
diff --git a/fs/file.c b/fs/file.c
index fc0eeb812e2c..e578e5537c32 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -538,6 +538,7 @@ int __alloc_fd(struct files_struct *files,
 	spin_unlock(&files->file_lock);
 	return error;
 }
+EXPORT_SYMBOL_GPL(__alloc_fd);
 
 static int alloc_fd(unsigned start, unsigned flags)
 {
@@ -611,6 +612,7 @@ void __fd_install(struct files_struct *files, unsigned int fd,
 	rcu_assign_pointer(fdt->fd[fd], file);
 	rcu_read_unlock_sched();
 }
+EXPORT_SYMBOL_GPL(__fd_install);
 
 void fd_install(unsigned int fd, struct file *file)
 {
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b0abe21d6cc9..1470be496ad2 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -24,6 +24,7 @@ struct linux_binprm {
 	struct page *page[MAX_ARG_PAGES];
 #endif
 	struct mm_struct *mm;
+	struct files_struct *new_files;
 	unsigned long p; /* current top of mem */
 	unsigned int
 		/*