From 9c572a83037a7dcd653ba3a9cc468c16b857d0c9 Mon Sep 17 00:00:00 2001 From: Bernard Ladenthin Date: Fri, 18 Sep 2026 15:39:37 +0200 Subject: [PATCH] net/sched: fix potential stack infoleak in em_text_dump() em_text_dump() allocates struct tcf_em_text on the stack without zeroing it. strscpy() writes the algorithm name and a NUL terminator into conf.algo[], leaving the remaining bytes uninitialised. nla_put_nohdr() then copies the full struct to the netlink response. KMSAN on Linux 7.2-rc6 reports two kernel-infoleak splats from this path, one triggered via "tc filter show" and one via a raw RTM_GETTFILTER dump: BUG: KMSAN: kernel-infoleak in _copy_to_iter+0x1c9/0x2620 nla_put_nohdr+0x83/0x130 em_text_dump+0x291/0x550 Local variable conf created at: em_text_dump+0x5d/0x550 Bytes 168-179 of 199 are uninitialized I am not certain whether this constitutes a real security problem in practice: the test was conducted in a controlled KMSAN environment and the leaked stack bytes may or may not carry sensitive data on actual production kernels. I am reporting it because KMSAN flagged it as a kernel-infoleak and the fix is straightforward. I can provide a userspace reproducer on request. The original code used strncpy() which zero-pads to the destination size. Commit b04202d6065c ("net/sched: replace strncpy with strscpy") replaced it with strscpy(), which does not pad, creating this condition. Zero-initialising the struct closes it. Fixes: b04202d6065c ("net/sched: replace strncpy with strscpy") Link: https://lore.kernel.org/netdev/20250327143733.187438-1-richard120310@gmail.com/ Assisted-by: Claude:claude-sonnet-4-6 [KMSAN] Signed-off-by: Bernard Ladenthin Acked-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260918133953.12494-1-bernard.ladenthin@gmail.com Signed-off-by: Jakub Kicinski --- net/sched/em_text.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/sched/em_text.c b/net/sched/em_text.c index 343f1aebeec2..4132f8c3c5fc 100644 --- a/net/sched/em_text.c +++ b/net/sched/em_text.c @@ -113,7 +113,7 @@ static void em_text_destroy(struct tcf_ematch *m) static int em_text_dump(struct sk_buff *skb, struct tcf_ematch *m) { struct text_match *tm = EM_TEXT_PRIV(m); - struct tcf_em_text conf; + struct tcf_em_text conf = {}; strscpy(conf.algo, tm->config->ops->name); conf.from_offset = tm->from_offset;