From 72b790c417b9f6ffec9d04b77b29103f451725f6 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 28 Mar 2019 20:43:30 -0700 Subject: fs/open.c: allow opening only regular files during execve() commit 73601ea5b7b18eb234219ae2adf77530f389da79 upstream. 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 Fixes: 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()") Signed-off-by: Tetsuo Handa Acked-by: Kees Cook Cc: Al Viro Cc: Eric Biggers Cc: Dmitry Vyukov Cc: [4.9+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/open.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs') 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)) -- cgit v1.2.3