+ fs-allow-opening-only-regular-files-during-execve.patch added to -mm tree

+ fs-allow-opening-only-regular-files-during-execve.patch added to -mm tree

[akpm]

The patch titled
     Subject: fs/open.c: allow opening only regular files during execve()
has been added to the -mm tree.  Its filename is
     fs-allow-opening-only-regular-files-during-execve.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/fs-allow-opening-only-regular-files-during-execve.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/fs-allow-opening-only-regular-files-during-execve.patch

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------------------------------------------------------
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Subject: fs/open.c: allow opening only regular files during execve()

syzbot is hitting lockdep warning [1] due to trying to open a fifo during
an execve() operation.  But we don't need to open non regular files during
an execve() operation, for all files which we will need are the executable
file itself and the interpreter programs like /bin/sh and ld-linux.so.2 .

Since the manpage for execve(2) says that execve() returns EACCES when the
file or a script interpreter is not a regular file, and the manpage for
uselib(2) says that uselib() can return EACCES, and we use FMODE_EXEC when
opening for execve()/uselib(), we can bail out if a non regular file is
requested with FMODE_EXEC set.

Since this deadlock followed by khungtaskd warnings is trivially
reproducible by a local unprivileged user, and syzbot's frequent crash due
to this deadlock defers finding other bugs, let's workaround this deadlock
until we get a chance to find a better solution.

[1] https://syzkaller.appspot.com/bug?id=b5095bfec44ec84213bac54742a82483aad578ce

Link: http://lkml.kernel.org/r/1552044017-7890-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp
Reported-by: syzbot <syzbot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@syzkaller.appspotmail.com>
Fixes: 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Biggers <ebiggers3@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>	[4.9+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/fs/open.c~fs-allow-opening-only-regular-files-during-execve
+++ a/fs/open.c
@@ -733,6 +733,12 @@ static int do_dentry_open(struct file *f
 		return 0;
 	}
 
+	/* Any file opened for execve()/uselib() has to be a regular file. */
+	if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
+		error = -EACCES;
+		goto cleanup_file;
+	}
+
 	if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
 		error = get_write_access(inode);
 		if (unlikely(error))
_

Patches currently in -mm which might be from penguin-kernel@I-love.SAKURA.ne.jp are

fs-allow-opening-only-regular-files-during-execve.patch
info-task-hung-in-generic_file_write_iter.patch
info-task-hung-in-generic_file_write-fix.patch