From: Eric Sandeen <sandeen@redhat.com>
To: fsdevel <linux-fsdevel@vger.kernel.org>
Cc: David Howells <dhowells@redhat.com>
Subject: [PATCH] fscache: Fix cookie key uninit mem / out of bound read
Date: Thu, 6 Sep 2018 10:31:11 -0500 [thread overview]
Message-ID: <630f5ad3-1751-1e75-6aa7-13e8b6f30aa4@redhat.com> (raw)
fscache_set_key() seems to have 2 issues related to the memory
read for hashing in fscache_set_key.
The first reported was a KASAN error,
BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x5b3/0x680 [fscache]
Read of size 4 at addr ffff88084ff056d4 by task mount.nfs/32615
also reported by syzbot at https://lkml.org/lkml/2018/7/8/236
BUG: KASAN: slab-out-of-bounds in fscache_set_key fs/fscache/cookie.c:120 [inline]
BUG: KASAN: slab-out-of-bounds in fscache_alloc_cookie+0x7a9/0x880 fs/fscache/cookie.c:171
Read of size 4 at addr ffff8801d3cc8bb4 by task syz-executor907/4466
This happens for any index_key_len which is not divisible by 4, and is
larger than the size of the inline key, because the code allocates exactly
index_key_len for the key buffer, but the hashing loop is stepping through
it 4 bytes (u32) at a time in the buf[] array.
When looking over this, it also appears that the inline key is
insufficiently initialized, zeroing only 3 of the 4 slots. Hence
an index_key_len between 13 and 15 bytes will end up hashing uninitialized
memory because the memcpy only partially fills the last buf[] element.
Fix this by calculating how many u32 buffers we'll need by using
DIV_ROUND_UP, and memset them all to zero before copying in the index_key,
then using that same count as the hashing index limit.
Reported-by: syzbot+a95b989b2dde8e806af8@syzkaller.appspotmail.com
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---
nb: compile-tested only, sorry.
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index 83bfe04..bc74ae3 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -83,7 +83,7 @@ void fscache_cookie_init_once(void *_cookie)
}
/*
- * Set the index key in a cookie. The cookie struct has space for a 12-byte
+ * Set the index key in a cookie. The cookie struct has space for a 16-byte
* key plus length and hash, but if that's not big enough, it's instead a
* pointer to a buffer containing 3 bytes of hash, 1 byte of length and then
* the key data.
@@ -93,22 +93,22 @@ static int fscache_set_key(struct fscache_cookie *cookie,
{
unsigned long long h;
u32 *buf;
+ int bufs;
int i;
cookie->key_len = index_key_len;
+ bufs = DIV_ROUND_UP(index_key_len, sizeof(*buf));
if (index_key_len > sizeof(cookie->inline_key)) {
- buf = kzalloc(index_key_len, GFP_KERNEL);
+ buf = kmalloc_array(bufs, sizeof(*buf), GFP_KERNEL);
if (!buf)
return -ENOMEM;
cookie->key = buf;
} else {
buf = (u32 *)cookie->inline_key;
- buf[0] = 0;
- buf[1] = 0;
- buf[2] = 0;
}
+ memset(buf, 0, bufs * sizeof(*buf));
memcpy(buf, index_key, index_key_len);
/* Calculate a hash and combine this with the length in the first word
@@ -116,7 +116,8 @@ static int fscache_set_key(struct fscache_cookie *cookie,
*/
h = (unsigned long)cookie->parent;
h += index_key_len + cookie->type;
- for (i = 0; i < (index_key_len + sizeof(u32) - 1) / sizeof(u32); i++)
+
+ for (i = 0; i < bufs; i++)
h += buf[i];
cookie->key_hash = h ^ (h >> 32);
next reply other threads:[~2018-09-06 20:07 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 15:31 Eric Sandeen [this message]
2018-09-25 19:25 ` [PATCH] fscache: Fix cookie key uninit mem / out of bound read Eric Sandeen
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