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pipe: actually allow root to exceed the pipe buffer limits 

commit 85c2dd5473b2718b4b63e74bfeb1ca876868e11f upstream.

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.

Link: http://lkml.kernel.org/r/20180111052902.14409-4-ebiggers3@gmail.com
Fixes: 759c01142a5d ("pipe: limit the per-user amount of pages allocated in pipes")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Luis R . Rodriguez" <mcgrof@kernel.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
This commit is contained in:
Eric Biggers 2018-02-06 15:41:53 -08:00 committed by syphyr
parent f32040ce1c
commit b037483c89
1 changed files with 8 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/pipe.c
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@ -811,6 +811,11 @@ 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;
@ -827,12 +832,12 @@ 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),
@ -1263,7 +1268,7 @@ 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;
}