CVE-2024-26766

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

IB/hfi1: Fix sdma.h tx->num_descs off-by-one error

Unfortunately the commit `fd8958efe877` introduced another error

causing the `descs` array to overflow. This reults in further crashes

easily reproducible by `sendmsg` system call.

[ 1080.836473] general protection fault, probably for non-canonical address 0x400300015528b00a: 0000 [#1] PREEMPT SMP PTI

[ 1080.869326] RIP: 0010:hfi1_ipoib_build_ib_tx_headers.constprop.0+0xe1/0x2b0 [hfi1]

--

[ 1080.974535] Call Trace:

[ 1080.976990] <TASK>

[ 1081.021929] hfi1_ipoib_send_dma_common+0x7a/0x2e0 [hfi1]

[ 1081.027364] hfi1_ipoib_send_dma_list+0x62/0x270 [hfi1]

[ 1081.032633] hfi1_ipoib_send+0x112/0x300 [hfi1]

[ 1081.042001] ipoib_start_xmit+0x2a9/0x2d0 [ib_ipoib]

[ 1081.046978] dev_hard_start_xmit+0xc4/0x210

--

[ 1081.148347] __sys_sendmsg+0x59/0xa0

crash> ipoib_txreq 0xffff9cfeba229f00

struct ipoib_txreq {

txreq = {

list = {

next = 0xffff9cfeba229f00,

prev = 0xffff9cfeba229f00

},

descp = 0xffff9cfeba229f40,

coalesce_buf = 0x0,

wait = 0xffff9cfea4e69a48,

complete = 0xffffffffc0fe0760 <hfi1_ipoib_sdma_complete>,

packet_len = 0x46d,

tlen = 0x0,

num_desc = 0x0,

desc_limit = 0x6,

next_descq_idx = 0x45c,

coalesce_idx = 0x0,

flags = 0x0,

descs = {{

qw = {0x8024000120dffb00, 0x4} # SDMA_DESC0_FIRST_DESC_FLAG (bit 63)

}, {

qw = { 0x3800014231b108, 0x4}

}, {

qw = { 0x310000e4ee0fcf0, 0x8}

}, {

qw = { 0x3000012e9f8000, 0x8}

}, {

qw = { 0x59000dfb9d0000, 0x8}

}, {

qw = { 0x78000e02e40000, 0x8}

}}

},

sdma_hdr = 0x400300015528b000, <<< invalid pointer in the tx request structure

sdma_status = 0x0, SDMA_DESC0_LAST_DESC_FLAG (bit 62)

complete = 0x0,

priv = 0x0,

txq = 0xffff9cfea4e69880,

skb = 0xffff9d099809f400

}

If an SDMA send consists of exactly 6 descriptors and requires dword

padding (in the 7th descriptor), the sdma_txreq descriptor array is not

properly expanded and the packet will overflow into the container

structure. This results in a panic when the send completion runs. The

exact panic varies depending on what elements of the container structure

get corrupted. The fix is to use the correct expression in

_pad_sdma_tx_descs() to test the need to expand the descriptor array.

With this patch the crashes are no longer reproducible and the machine is

stable.