[PATCH 5.16 0914/1017] ubifs: Fix read out-of-bounds in ubifs_wbuf_write_nolock()

Greg Kroah-Hartman
2022-04-05T10:27:43Z

From: Zhihao Cheng <chengzhihao1@huawei.com>

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>
---
fs/ubifs/io.c | 34 ++++++++++++++++++++++++++++++----
1 file changed, 30 insertions(+), 4 deletions(-)

--- a/fs/ubifs/io.c
+++ b/fs/ubifs/io.c
@@ -833,16 +833,42 @@ int ubifs_wbuf_write_nolock(struct ubifs
*/
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;
}