linux-kernel - [PATCH 2/3] get_signal: hide_si_addr_tag_bits: fix the usage of uninitialized ksig

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Date: Mon, 26 Feb 2024 17:56:50 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
	Christian Brauner <brauner@...nel.org>,
	Peter Collingbourne <pcc@...gle.com>,
	Wen Yang <wenyang.linux@...mail.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] get_signal: hide_si_addr_tag_bits: fix the usage of
 uninitialized ksig

ksig->ka and ksig->info are not initialized if get_signal() returns 0 or
if the caller is PF_USER_WORKER.

Check signr != 0 before SA_EXPOSE_TAGBITS and move the "out" label down.

The latter means that ksig->sig won't be initialized if a PF_USER_WORKER
thread gets a fatal signal but this is fine, PF_USER_WORKER's don't use
ksig. And there is nothing new, in this case ksig->ka and ksig-info are
not initialized anyway. Add a comment.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/signal.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 09a6dd07cf6b..a69d3069067a 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2881,8 +2881,9 @@ bool get_signal(struct ksignal *ksig)
 
 		/*
 		 * PF_USER_WORKER threads will catch and exit on fatal signals
-		 * themselves. They have cleanup that must be performed, so
-		 * we cannot call do_exit() on their behalf.
+		 * themselves. They have cleanup that must be performed, so we
+		 * cannot call do_exit() on their behalf. Note that ksig won't
+		 * be properly initialized, PF_USER_WORKER's shouldn't use it.
 		 */
 		if (current->flags & PF_USER_WORKER)
 			goto out;
@@ -2894,12 +2895,12 @@ bool get_signal(struct ksignal *ksig)
 		/* NOTREACHED */
 	}
 	spin_unlock_irq(&sighand->siglock);
-out:
+
 	ksig->sig = signr;
 
-	if (!(ksig->ka.sa.sa_flags & SA_EXPOSE_TAGBITS))
+	if (signr && !(ksig->ka.sa.sa_flags & SA_EXPOSE_TAGBITS))
 		hide_si_addr_tag_bits(ksig);
-
+out:
 	return signr > 0;
 }
 
-- 
2.25.1.362.g51ebf55