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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.19 105/106] kexec: bail out upon SIGKILL when allocating memory.
Date:   Sun,  6 Oct 2019 19:21:51 +0200
Message-Id: <20191006171204.889444159@linuxfoundation.org>
In-Reply-To: <20191006171124.641144086@linuxfoundation.org>
References: <20191006171124.641144086@linuxfoundation.org>
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From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit 7c3a6aedcd6aae0a32a527e68669f7dd667492d1 upstream.

syzbot found that a thread can stall for minutes inside kexec_load() after
that thread was killed by SIGKILL [1].  It turned out that the reproducer
was trying to allocate 2408MB of memory using kimage_alloc_page() from
kimage_load_normal_segment().  Let's check for SIGKILL before doing memory
allocation.

[1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e

Link: http://lkml.kernel.org/r/993c9185-d324-2640-d061-bed2dd18b1f7@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+8ab2d0f39fb79fe6ca40@syzkaller.appspotmail.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/kexec_core.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -301,6 +301,8 @@ static struct page *kimage_alloc_pages(g
 {
 	struct page *pages;
 
+	if (fatal_signal_pending(current))
+		return NULL;
 	pages = alloc_pages(gfp_mask & ~__GFP_ZERO, order);
 	if (pages) {
 		unsigned int count, i;