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tracing: Fix buffer_ref pipe ops 

This is preparation for fixing CVE-2019-11487.
This commit is contained in:
Ben Hutchings 2019-05-05 15:42:32 +01:00
parent 4f3fa1e296
commit 83f5e0f1ef
3 changed files with 139 additions and 0 deletions
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1
debian/changelog vendored
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@ -1110,6 +1110,7 @@ linux (4.19.37-1) UNRELEASED; urgency=medium
- aio: keep io_event in aio_kiocb
- aio: store event at final iocb_put()
- Fix aio_poll() races
* tracing: Fix buffer_ref pipe ops
[ YunQiang Su ]
* [mips*r6] Re-enable CONFIG_JUMP_LABEL, which has been fixed in upstream.

137
debian/patches/bugfix/all/tracing-fix-buffer_ref-pipe-ops.patch vendored Normal file
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@ -0,0 +1,137 @@
From: Jann Horn <jannh@google.com>
Date: Thu, 4 Apr 2019 23:59:25 +0200
Subject: tracing: Fix buffer_ref pipe ops
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit?id=cffeb9c84d20816a2173e3cfeca210c8bfa8e357
commit b987222654f84f7b4ca95b3a55eca784cb30235b upstream.
This fixes multiple issues in buffer_pipe_buf_ops:
- The ->steal() handler must not return zero unless the pipe buffer has
the only reference to the page. But generic_pipe_buf_steal() assumes
that every reference to the pipe is tracked by the page's refcount,
which isn't true for these buffers - buffer_pipe_buf_get(), which
duplicates a buffer, doesn't touch the page's refcount.
Fix it by using generic_pipe_buf_nosteal(), which refuses every
attempted theft. It should be easy to actually support ->steal, but the
only current users of pipe_buf_steal() are the virtio console and FUSE,
and they also only use it as an optimization. So it's probably not worth
the effort.
- The ->get() and ->release() handlers can be invoked concurrently on pipe
buffers backed by the same struct buffer_ref. Make them safe against
concurrency by using refcount_t.
- The pointers stored in ->private were only zeroed out when the last
reference to the buffer_ref was dropped. As far as I know, this
shouldn't be necessary anyway, but if we do it, let's always do it.
Link: http://lkml.kernel.org/r/20190404215925.253531-1-jannh@google.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
Fixes: 73a757e63114d ("ring-buffer: Return reader page back into existing ring buffer")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/splice.c | 4 ++--
include/linux/pipe_fs_i.h | 1 +
kernel/trace/trace.c | 28 ++++++++++++++--------------
3 files changed, 17 insertions(+), 16 deletions(-)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -333,8 +333,8 @@ const struct pipe_buf_operations default
.get = generic_pipe_buf_get,
};
-static int generic_pipe_buf_nosteal(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf)
+int generic_pipe_buf_nosteal(struct pipe_inode_info *pipe,
+ struct pipe_buffer *buf)
{
return 1;
}
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -181,6 +181,7 @@ void free_pipe_info(struct pipe_inode_in
void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
+int generic_pipe_buf_nosteal(struct pipe_inode_info *, struct pipe_buffer *);
void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6800,19 +6800,23 @@ struct buffer_ref {
struct ring_buffer *buffer;
void *page;
int cpu;
- int ref;
+ refcount_t refcount;
};
+static void buffer_ref_release(struct buffer_ref *ref)
+{
+ if (!refcount_dec_and_test(&ref->refcount))
+ return;
+ ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
+ kfree(ref);
+}
+
static void buffer_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct buffer_ref *ref = (struct buffer_ref *)buf->private;
- if (--ref->ref)
- return;
-
- ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
- kfree(ref);
+ buffer_ref_release(ref);
buf->private = 0;
}
@@ -6821,7 +6825,7 @@ static void buffer_pipe_buf_get(struct p
{
struct buffer_ref *ref = (struct buffer_ref *)buf->private;
- ref->ref++;
+ refcount_inc(&ref->refcount);
}
/* Pipe buffer operations for a buffer. */
@@ -6829,7 +6833,7 @@ static const struct pipe_buf_operations
.can_merge = 0,
.confirm = generic_pipe_buf_confirm,
.release = buffer_pipe_buf_release,
- .steal = generic_pipe_buf_steal,
+ .steal = generic_pipe_buf_nosteal,
.get = buffer_pipe_buf_get,
};
@@ -6842,11 +6846,7 @@ static void buffer_spd_release(struct sp
struct buffer_ref *ref =
(struct buffer_ref *)spd->partial[i].private;
- if (--ref->ref)
- return;
-
- ring_buffer_free_read_page(ref->buffer, ref->cpu, ref->page);
- kfree(ref);
+ buffer_ref_release(ref);
spd->partial[i].private = 0;
}
@@ -6901,7 +6901,7 @@ tracing_buffers_splice_read(struct file
break;
}
- ref->ref = 1;
+ refcount_set(&ref->refcount, 1);
ref->buffer = iter->trace_buffer->buffer;
ref->page = ring_buffer_alloc_read_page(ref->buffer, iter->cpu_file);
if (IS_ERR(ref->page)) {

1
debian/patches/series vendored
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@ -176,6 +176,7 @@ bugfix/all/0011-aio-fold-lookup_kiocb-into-its-sole-caller.patch
bugfix/all/0012-aio-keep-io_event-in-aio_kiocb.patch
bugfix/all/0013-aio-store-event-at-final-iocb_put.patch
bugfix/all/0014-Fix-aio_poll-races.patch
bugfix/all/tracing-fix-buffer_ref-pipe-ops.patch
# Fix exported symbol versions
bugfix/all/module-disable-matching-missing-version-crc.patch