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From: Eric Biggers <ebiggers3@gmail.com>
To: linux-fsdevel@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Willy Tarreau <w@1wt.eu>, Mikulas Patocka <mpatocka@redhat.com>,
	"Luis R . Rodriguez" <mcgrof@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	linux-kernel@vger.kernel.org, Eric Biggers <ebiggers@google.com>,
	stable@vger.kernel.org
Subject: [PATCH v2 3/7] pipe: actually allow root to exceed the pipe buffer limits
Date: Wed, 10 Jan 2018 21:28:58 -0800	[thread overview]
Message-ID: <20180111052902.14409-4-ebiggers3@gmail.com> (raw)
In-Reply-To: <20180111052902.14409-1-ebiggers3@gmail.com>

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.

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

  parent reply	other threads:[~2018-01-11  5:28 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-11  5:28 [PATCH v2 0/7] pipe: buffer limits fixes and cleanups Eric Biggers
2018-01-11  5:28 ` [PATCH v2 1/7] pipe, sysctl: drop 'min' parameter from pipe-max-size converter Eric Biggers
2018-01-11  5:28 ` [PATCH v2 2/7] pipe, sysctl: remove pipe_proc_fn() Eric Biggers
2018-01-11  5:28 ` Eric Biggers [this message]
2018-01-11  5:28 ` [PATCH v2 4/7] pipe: fix off-by-one error when checking buffer limits Eric Biggers
2018-01-11  5:29 ` [PATCH v2 5/7] pipe: reject F_SETPIPE_SZ with size over UINT_MAX Eric Biggers
2018-01-11  5:29 ` [PATCH v2 6/7] pipe: simplify round_pipe_size() Eric Biggers
2018-01-11  5:29 ` [PATCH v2 7/7] pipe: read buffer limits atomically Eric Biggers
2018-01-11 20:36 ` [PATCH v2 0/7] pipe: buffer limits fixes and cleanups Kees Cook
2018-01-11 21:41 ` Joe Lawrence

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