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

In the Linux kernel, the following vulnerability has been resolved:

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

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].