The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 20f1431160c6b590cdc269a846fc5a448abf5b98 Mon Sep 17 00:00:00 2001

From: Richard Weinberger richard@nod.at Date: Mon, 16 Nov 2020 22:05:30 +0100 Subject: [PATCH] ubifs: wbuf: Don't leak kernel memory to flash

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

diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c index 2dc933f73165..a9cabb3fa64c 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;