ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()

commit 4f2262a334641e05f645364d5ade1f565c85f20b upstream.

Function ubifs_wbuf_write_nolock() may access buf out of bounds in
following process:

ubifs_wbuf_write_nolock():
  aligned_len = ALIGN(len, 8);   // Assume len = 4089, aligned_len = 4096
  if (aligned_len <= wbuf->avail) ... // Not satisfy
  if (wbuf->used) {
    ubifs_leb_write()  // Fill some data in avail wbuf
    len -= wbuf->avail;   // len is still not 8-bytes aligned
    aligned_len -= wbuf->avail;
  }
  n = aligned_len >> c->max_write_shift;
  if (n) {
    n <<= c->max_write_shift;
    err = ubifs_leb_write(c, wbuf->lnum, buf + written,
                          wbuf->offs, n);
    // n > len, read out of bounds less than 8(n-len) bytes
  }

, which can be catched by KASAN:
  =========================================================
  BUG: KASAN: slab-out-of-bounds in ecc_sw_hamming_calculate+0x1dc/0x7d0
  Read of size 4 at addr ffff888105594ff8 by task kworker/u8:4/128
  Workqueue: writeback wb_workfn (flush-ubifs_0_0)
  Call Trace:
    kasan_report.cold+0x81/0x165
    nand_write_page_swecc+0xa9/0x160
    ubifs_leb_write+0xf2/0x1b0 [ubifs]
    ubifs_wbuf_write_nolock+0x421/0x12c0 [ubifs]
    write_head+0xdc/0x1c0 [ubifs]
    ubifs_jnl_write_inode+0x627/0x960 [ubifs]
    wb_workfn+0x8af/0xb80

Function ubifs_wbuf_write_nolock() accepts that parameter 'len' is not 8
bytes aligned, the 'len' represents the true length of buf (which is
allocated in 'ubifs_jnl_xxx', eg. ubifs_jnl_write_inode), so
ubifs_wbuf_write_nolock() must handle the length read from 'buf' carefully
to write leb safely.

Fetch a reproducer in [Link].

Fixes: 1e51764a3c2ac0 ("UBIFS: add new flash file system")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=214785
Reported-by: Chengsong Ke <kechengsong@huawei.com>
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ubifs/io.c b/fs/ubifs/io.c
index 00b61db..b019dd6 100644 (file)
--- a/fs/ubifs/io.c
+++ b/fs/ubifs/io.c
@@ -833,16 +833,42 @@ int ubifs_wbuf_write_nolock(struct ubifs_wbuf *wbuf, void *buf, int len)
         */
        n = aligned_len >> c->max_write_shift;
        if (n) {
-               n <<= c->max_write_shift;
+               int m = n - 1;
+
                dbg_io("write %d bytes to LEB %d:%d", n, wbuf->lnum,
                       wbuf->offs);
-               err = ubifs_leb_write(c, wbuf->lnum, buf + written,
-                                     wbuf->offs, n);
+
+               if (m) {
+                       /* '(n-1)<<c->max_write_shift < len' is always true. */
+                       m <<= c->max_write_shift;
+                       err = ubifs_leb_write(c, wbuf->lnum, buf + written,
+                                             wbuf->offs, m);
+                       if (err)
+                               goto out;
+                       wbuf->offs += m;
+                       aligned_len -= m;
+                       len -= m;
+                       written += m;
+               }
+
+               /*
+                * The non-written len of buf may be less than 'n' because
+                * parameter 'len' is not 8 bytes aligned, so here we read
+                * min(len, n) bytes from buf.
+                */
+               n = 1 << c->max_write_shift;
+               memcpy(wbuf->buf, buf + written, min(len, n));
+               if (n > len) {
+                       ubifs_assert(c, n - len < 8);
+                       ubifs_pad(c, wbuf->buf + len, n - len);
+               }
+
+               err = ubifs_leb_write(c, wbuf->lnum, wbuf->buf, wbuf->offs, n);
                if (err)
                        goto out;
                wbuf->offs += n;
                aligned_len -= n;
-               len -= n;
+               len -= min(len, n);
                written += n;
        }