Patch "fs: Don't dump core if the corefile would become world-readable." has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    fs: Don't dump core if the corefile would become world-readable.

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fs-don-t-dump-core-if-the-corefile-would-become-world-readable.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 40f705a736eac10e7dca7ab5dd5ed675a6df031d Mon Sep 17 00:00:00 2001
From: Jann Horn <jann@thejh.net>
Date: Wed, 9 Sep 2015 15:38:30 -0700
Subject: fs: Don't dump core if the corefile would become world-readable.

From: Jann Horn <jann@thejh.net>

commit 40f705a736eac10e7dca7ab5dd5ed675a6df031d upstream.

On a filesystem like vfat, all files are created with the same owner
and mode independent of who created the file. When a vfat filesystem
is mounted with root as owner of all files and read access for everyone,
root's processes left world-readable coredumps on it (but other
users' processes only left empty corefiles when given write access
because of the uid mismatch).

Given that the old behavior was inconsistent and insecure, I don't see
a problem with changing it. Now, all processes refuse to dump core unless
the resulting corefile will only be readable by their owner.

Signed-off-by: Jann Horn <jann@thejh.net>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/coredump.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -685,11 +685,15 @@ void do_coredump(const siginfo_t *siginf
 		if (!S_ISREG(inode->i_mode))
 			goto close_fail;
 		/*
-		 * Dont allow local users get cute and trick others to coredump
-		 * into their pre-created files.
+		 * Don't dump core if the filesystem changed owner or mode
+		 * of the file during file creation. This is an issue when
+		 * a process dumps core while its cwd is e.g. on a vfat
+		 * filesystem.
 		 */
 		if (!uid_eq(inode->i_uid, current_fsuid()))
 			goto close_fail;
+		if ((inode->i_mode & 0677) != 0600)
+			goto close_fail;
 		if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
 			goto close_fail;
 		if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))


Patches currently in stable-queue which might be from jann@thejh.net are

queue-4.2/fs-if-a-coredump-already-exists-unlink-and-recreate-with-o_excl.patch
queue-4.2/fs-don-t-dump-core-if-the-corefile-would-become-world-readable.patch
queue-4.2/cifs-fix-type-confusion-in-copy-offload-ioctl.patch