[PATCH 5.10 002/147] RDMA/umad: Reject negative data_len in ib_umad_write

Sasha Levin
2026-02-28T18:17:38Z

From: YunJe Shin <yjshin0438@gmail.com>

commit 5551b02fdbfd85a325bb857f3a8f9c9f33397ed2 upstream.

ib_umad_write computes data_len from user-controlled count and the
MAD header sizes. With a mismatched user MAD header size and RMPP
header length, data_len can become negative and reach ib_create_send_mad().
This can make the padding calculation exceed the segment size and trigger
an out-of-bounds memset in alloc_send_rmpp_list().

Add an explicit check to reject negative data_len before creating the
send buffer.

KASAN splat:
[ 211.363464] BUG: KASAN: slab-out-of-bounds in ib_create_send_mad+0xa01/0x11b0
[ 211.364077] Write of size 220 at addr ffff88800c3fa1f8 by task spray_thread/102
[ 211.365867] ib_create_send_mad+0xa01/0x11b0
[ 211.365887] ib_umad_write+0x853/0x1c80

Fixes: 2be8e3ee8efd ("IB/umad: Add P_Key index support")
Signed-off-by: YunJe Shin <ioerts@kookmin.ac.kr>
Link: https://patch.msgid.link/20260203100628.1215408-1-ioerts@kookmin.ac.kr
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/infiniband/core/user_mad.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/user_mad.c b/drivers/infiniband/core/user_mad.c
index 063707dd4fe37..c8ad6ef39fa55 100644
--- a/drivers/infiniband/core/user_mad.c
+++ b/drivers/infiniband/core/user_mad.c
@@ -514,7 +514,8 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
struct rdma_ah_attr ah_attr;
struct ib_ah *ah;
__be64 *tid;
- int ret, data_len, hdr_len, copy_offset, rmpp_active;
+ int ret, hdr_len, copy_offset, rmpp_active;
+ size_t data_len;
u8 base_version;

if (count < hdr_size(file) + IB_MGMT_RMPP_HDR)
@@ -588,7 +589,10 @@ static ssize_t ib_umad_write(struct file *filp, const char __user *buf,
}

base_version = ((struct ib_mad_hdr *)&packet->mad.data)->base_version;
- data_len = count - hdr_size(file) - hdr_len;
+ if (check_sub_overflow(count, hdr_size(file) + hdr_len, &data_len)) {
+ ret = -EINVAL;
+ goto err_ah;
+ }
packet->msg = ib_create_send_mad(agent,
be32_to_cpu(packet->mad.hdr.qpn),
packet->mad.hdr.pkey_index, rmpp_active,
--
2.51.0