From 73601ea5b7b18eb234219ae2adf77530f389da79 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Thu, 28 Mar 2019 20:43:30 -0700
Subject: [PATCH] fs/open.c: allow opening only regular files during execve()
Git-commit: 73601ea5b7b18eb234219ae2adf77530f389da79
Patch-mainline: v5.1-rc3
References: bsc#1163845
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Jan Kara <jack@suse.cz>
---
fs/open.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/open.c b/fs/open.c
index 0285ce7dbd51..f1c2f855fd43 100644
--- a/fs/open.c
+++ b/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))
--
2.16.4