On Sun, Jan 7, 2018 at 9:35 PM, Eric Biggers ebiggers3@gmail.com wrote:

From: Eric Biggers ebiggers@google.com

pipe-user-pages-hard and pipe-user-pages-soft are only supposed to apply to unprivileged users, as documented in both Documentation/sysctl/fs.txt and the pipe(7) man page.

However, the capabilities are actually only checked when increasing a pipe's size using F_SETPIPE_SZ, not when creating a new pipe. Therefore, if pipe-user-pages-hard has been set, the root user can run into it and be unable to create pipes. Similarly, if pipe-user-pages-soft has been set, the root user can run into it and have their pipes limited to 1 page each.

Fix this by allowing the privileged override in both cases.

Should this be controlled per-namespace instead of via init-ns caps?

-Kees

Fixes: 759c01142a5d ("pipe: limit the per-user amount of pages allocated in pipes") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com

---

fs/pipe.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c index d0dec5e7ef33..847ecc388820 100644 --- a/fs/pipe.c +++ b/fs/pipe.c @@ -613,6 +613,11 @@ static bool too_many_pipe_buffers_hard(unsigned long user_bufs) return pipe_user_pages_hard && user_bufs >= pipe_user_pages_hard; }

+static bool is_unprivileged_user(void) +{

•   return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
  

+}

struct pipe_inode_info *alloc_pipe_info(void) { struct pipe_inode_info *pipe; @@ -629,12 +634,12 @@ struct pipe_inode_info *alloc_pipe_info(void)

    user_bufs = account_pipe_buffers(user, 0, pipe_bufs);

•   if (too_many_pipe_buffers_soft(user_bufs)) {
  

•   if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) {
            user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
            pipe_bufs = 1;
    }
  
  

•   if (too_many_pipe_buffers_hard(user_bufs))
  

•   if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())
            goto out_revert_acct;
  
    pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
  

@@ -1065,7 +1070,7 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) if (nr_pages > pipe->buffers && (too_many_pipe_buffers_hard(user_bufs) || too_many_pipe_buffers_soft(user_bufs)) &&

•                   !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN)) {
  

•                   is_unprivileged_user()) {
            ret = -EPERM;
            goto out_revert_acct;
    }
  

-- 2.15.1