CVE-2021-47636 Information

Description

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].

Reference

https://git.kernel.org/stable/c/07a209fadee7b53b46858538e1177597273862e4 https://git.kernel.org/stable/c/3b7fb89135a20587d57f8877c02e25003e9edbdf https://git.kernel.org/stable/c/4f2262a334641e05f645364d5ade1f565c85f20b https://git.kernel.org/stable/c/5343575aa11c5d7044107d59d43f84aec01312b0 https://git.kernel.org/stable/c/a7054aaf1909cf40489c0ec1b728fdcf79c751a6 https://git.kernel.org/stable/c/b80ccbec0e4804436c382d7dd60e943c386ed83a https://git.kernel.org/stable/c/e09fa5318d51f522e1af4fbaf8f74999355980c8