[PATCH 6.18 434/752] netconsole: avoid OOB reads, msg is not nul-terminated

Sasha Levin
2026-02-28T17:54:12Z

From: Jakub Kicinski <kuba@kernel.org>

[ Upstream commit 82aec772fca2223bc5774bd9af486fd95766e578 ]

msg passed to netconsole from the console subsystem is not guaranteed
to be nul-terminated. Before recent
commit 7eab73b18630 ("netconsole: convert to NBCON console infrastructure")
the message would be placed in printk_shared_pbufs, a static global
buffer, so KASAN had harder time catching OOB accesses. Now we see:

printk: console [netcon_ext0] enabled
BUG: KASAN: slab-out-of-bounds in string+0x1f7/0x240
Read of size 1 at addr ffff88813b6d4c00 by task pr/netcon_ext0/594

CPU: 65 UID: 0 PID: 594 Comm: pr/netcon_ext0 Not tainted 6.19.0-11754-g4246fd6547c9
Call Trace:
kasan_report+0xe4/0x120
string+0x1f7/0x240
vsnprintf+0x655/0xba0
scnprintf+0xba/0x120
netconsole_write+0x3fe/0xa10
nbcon_emit_next_record+0x46e/0x860
nbcon_kthread_func+0x623/0x750

Allocated by task 1:
nbcon_alloc+0x1ea/0x450
register_console+0x26b/0xe10
init_netconsole+0xbb0/0xda0

The buggy address belongs to the object at ffff88813b6d4000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 0 bytes to the right of
allocated 3072-byte region [ffff88813b6d4000, ffff88813b6d4c00)

Fixes: c62c0a17f9b7 ("netconsole: Append kernel version to message")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260219195021.2099699-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/netconsole.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index bb6e03a929565..020252961c906 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -1537,7 +1537,8 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt,
if (release_len) {
release = init_utsname()->release;

- scnprintf(nt->buf, MAX_PRINT_CHUNK, "%s,%s", release, msg);
+ scnprintf(nt->buf, MAX_PRINT_CHUNK, "%s,%.*s", release,
+ msg_len, msg);
msg_len += release_len;
} else {
memcpy(nt->buf, msg, msg_len);
--
2.51.0