[PATCH 4.19 311/346] ubifs: wbuf: Dont leak kernel memory to flash

Greg Kroah-Hartman
2020-12-28T13:35:28Z

From: Richard Weinberger <richard@nod.at>

commit 20f1431160c6b590cdc269a846fc5a448abf5b98 upstream.

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>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ubifs/io.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

--- a/fs/ubifs/io.c
+++ b/fs/ubifs/io.c
@@ -331,7 +331,7 @@ void ubifs_pad(const struct ubifs_info *
{
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;
@@ -728,6 +728,10 @@ int ubifs_wbuf_write_nolock(struct ubifs
* 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",
@@ -820,13 +824,18 @@ int ubifs_wbuf_write_nolock(struct ubifs
}

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;