| Message ID | 1552044017-7890-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,(resend)] fs: Allow opening only regular files during execve(). | expand |
On Fri, Mar 8, 2019 at 3:20 AM Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp> wrote: > > 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 > > Reported-by: syzbot <syzbot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@syzkaller.appspotmail.com> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > Fixes: 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()") > Cc: <stable@vger.kernel.org> # 4.9+ Acked-by: Kees Cook <keescook@chromium.org> Andrew, can you take this for -mm? -Kees > --- > fs/open.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/fs/open.c b/fs/open.c > index 0285ce7..f1c2f85 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)) > -- > 1.8.3.1 >
diff --git a/fs/open.c b/fs/open.c index 0285ce7..f1c2f85 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))
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 Reported-by: syzbot <syzbot+e93a80c1bb7c5c56e522461c149f8bf55eab1b2b@syzkaller.appspotmail.com> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Fixes: 8924feff66f35fe2 ("splice: lift pipe_lock out of splice_to_pipe()") Cc: <stable@vger.kernel.org> # 4.9+ --- fs/open.c | 6 ++++++ 1 file changed, 6 insertions(+)