[PATCH] ubifs: wbuf: Don't leak kernel memory to flash

[PATCH] ubifs: wbuf: Don't leak kernel memory to flash

[Richard Weinberger]

Write buffers use a kmalloc()'ed buffer, they can leak
up to seven bytes of kernel memory to flash if writes are not
aligned.
So use ubifs_pad() to fill these gaps with padding bytes.
This was never a problem while scanning because the scanner logic
manually aligns node lengths and skips over these gaps.

Cc: <stable@vger.kernel.org>
Fixes: 1e51764a3c2ac05a2 ("UBIFS: add new flash file system")
Signed-off-by: Richard Weinberger <richard@nod.at>
---
 fs/ubifs/io.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c
index 7e4bfaf2871f..eae9cf5a57b0 100644
--- a/fs/ubifs/io.c
+++ b/fs/ubifs/io.c
@@ -319,7 +319,7 @@ void ubifs_pad(const struct ubifs_info *c, void *buf, int pad)
 {
 	uint32_t crc;
 
-	ubifs_assert(c, pad >= 0 && !(pad & 7));
+	ubifs_assert(c, pad >= 0);
 
 	if (pad >= UBIFS_PAD_NODE_SZ) {
 		struct ubifs_ch *ch = buf;
@@ -764,6 +764,10 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
 		 * write-buffer.
 		 */
 		memcpy(wbuf->buf + wbuf->used, buf, len);
+		if (aligned_len > len) {
+			ubifs_assert(c, aligned_len - len < 8);
+			ubifs_pad(c, wbuf->buf + wbuf->used + len, aligned_len - len);
+		}
 
 		if (aligned_len == wbuf->avail) {
 			dbg_io("flush jhead %s wbuf to LEB %d:%d",
@@ -856,13 +860,18 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
 	}
 
 	spin_lock(&wbuf->lock);
-	if (aligned_len)
+	if (aligned_len) {
 		/*
 		 * And now we have what's left and what does not take whole
 		 * max. write unit, so write it to the write-buffer and we are
 		 * done.
 		 */
 		memcpy(wbuf->buf, buf + written, len);
+		if (aligned_len > len) {
+			ubifs_assert(c, aligned_len - len < 8);
+			ubifs_pad(c, wbuf->buf + len, aligned_len - len);
+		}
+	}
 
 	if (c->leb_size - wbuf->offs >= c->max_write_size)
 		wbuf->size = c->max_write_size;
-- 
2.26.2

Re: [PATCH] ubifs: wbuf: Don't leak kernel memory to flash

[Zhihao Cheng]

在 2020/11/17 5:05, Richard Weinberger 写道:
> Write buffers use a kmalloc()'ed buffer, they can leak
> up to seven bytes of kernel memory to flash if writes are not
> aligned.
> So use ubifs_pad() to fill these gaps with padding bytes.
> This was never a problem while scanning because the scanner logic
> manually aligns node lengths and skips over these gaps.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: 1e51764a3c2ac05a2 ("UBIFS: add new flash file system")
> Signed-off-by: Richard Weinberger <richard@nod.at>
> ---
>   fs/ubifs/io.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c
> index 7e4bfaf2871f..eae9cf5a57b0 100644
> --- a/fs/ubifs/io.c
> +++ b/fs/ubifs/io.c
> @@ -319,7 +319,7 @@ void ubifs_pad(const struct ubifs_info *c, void *buf, int pad)
>   {
>   	uint32_t crc;
>   
> -	ubifs_assert(c, pad >= 0 && !(pad & 7));
> +	ubifs_assert(c, pad >= 0);
>   
>   	if (pad >= UBIFS_PAD_NODE_SZ) {
>   		struct ubifs_ch *ch = buf;
> @@ -764,6 +764,10 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
>   		 * write-buffer.
>   		 */
>   		memcpy(wbuf->buf + wbuf->used, buf, len);
> +		if (aligned_len > len) {
> +			ubifs_assert(c, aligned_len - len < 8);
> +			ubifs_pad(c, wbuf->buf + wbuf->used + len, aligned_len - len);
> +		}
>   
>   		if (aligned_len == wbuf->avail) {
>   			dbg_io("flush jhead %s wbuf to LEB %d:%d",
> @@ -856,13 +860,18 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
>   	}
>   
>   	spin_lock(&wbuf->lock);
> -	if (aligned_len)
> +	if (aligned_len) {
>   		/*
>   		 * And now we have what's left and what does not take whole
>   		 * max. write unit, so write it to the write-buffer and we are
>   		 * done.
>   		 */
>   		memcpy(wbuf->buf, buf + written, len);
> +		if (aligned_len > len) {
> +			ubifs_assert(c, aligned_len - len < 8);
> +			ubifs_pad(c, wbuf->buf + len, aligned_len - len);
> +		}
> +	}
>   
>   	if (c->leb_size - wbuf->offs >= c->max_write_size)
>   		wbuf->size = c->max_write_size;
> 

Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>

Re: [PATCH] ubifs: wbuf: Don't leak kernel memory to flash

[Richard Weinberger]

On Tue, Nov 17, 2020 at 2:28 AM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>
> Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>

Thanks for reviewing, highly appreciated!

-- 
Thanks,
//richard

Re: [PATCH] ubifs: wbuf: Don't leak kernel memory to flash

[Zhihao Cheng]

在 2020/11/17 16:43, Richard Weinberger 写道:
> On Tue, Nov 17, 2020 at 2:28 AM Zhihao Cheng <chengzhihao1@huawei.com> wrote:
>>
>> Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
> 
> Thanks for reviewing, highly appreciated!
> 
You're welcome. Actually I've been following the linux-mtd. It's just 
that this patch isn't complicated, so I checked it. :-)