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=b5095bfec44ec84213bac54742a82483aad578c...

Link: http://lkml.kernel.org/r/1552044017-7890-1-git-send-email-penguin-kernel@I-l... 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 ---

fs/open.c | 6 ++++++ 1 file changed, 6 insertions(+)

--- 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)) _