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Message-Id: <20200331085440.233768523@linuxfoundation.org>
Date: Tue, 31 Mar 2020 10:59:39 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
syzbot+fcab69d1ada3e8d6f06b@...kaller.appspotmail.com,
Alexander Potapenko <glider@...gle.com>,
Eric Biggers <ebiggers@...gle.com>,
Kees Cook <keescook@...omium.org>
Subject: [PATCH 5.5 165/170] libfs: fix infoleak in simple_attr_read()
From: Eric Biggers <ebiggers@...gle.com>
commit a65cab7d7f05c2061a3e2490257d3086ff3202c6 upstream.
Reading from a debugfs file at a nonzero position, without first reading
at position 0, leaks uninitialized memory to userspace.
It's a bit tricky to do this, since lseek() and pread() aren't allowed
on these files, and write() doesn't update the position on them. But
writing to them with splice() *does* update the position:
#define _GNU_SOURCE 1
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
int pipes[2], fd, n, i;
char buf[32];
pipe(pipes);
write(pipes[1], "0", 1);
fd = open("/sys/kernel/debug/fault_around_bytes", O_RDWR);
splice(pipes[0], NULL, fd, NULL, 1, 0);
n = read(fd, buf, sizeof(buf));
for (i = 0; i < n; i++)
printf("%02x", buf[i]);
printf("\n");
}
Output:
5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a5a30
Fix the infoleak by making simple_attr_read() always fill
simple_attr::get_buf if it hasn't been filled yet.
Reported-by: syzbot+fcab69d1ada3e8d6f06b@...kaller.appspotmail.com
Reported-by: Alexander Potapenko <glider@...gle.com>
Fixes: acaefc25d21f ("[PATCH] libfs: add simple attribute files")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Acked-by: Kees Cook <keescook@...omium.org>
Link: https://lore.kernel.org/r/20200308023849.988264-1-ebiggers@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
fs/libfs.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -821,7 +821,7 @@ int simple_attr_open(struct inode *inode
{
struct simple_attr *attr;
- attr = kmalloc(sizeof(*attr), GFP_KERNEL);
+ attr = kzalloc(sizeof(*attr), GFP_KERNEL);
if (!attr)
return -ENOMEM;
@@ -861,9 +861,11 @@ ssize_t simple_attr_read(struct file *fi
if (ret)
return ret;
- if (*ppos) { /* continued read */
+ if (*ppos && attr->get_buf[0]) {
+ /* continued read */
size = strlen(attr->get_buf);
- } else { /* first read */
+ } else {
+ /* first read */
u64 val;
ret = attr->get(attr->data, &val);
if (ret)
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