linux-kernel - [PATCH 1/2] proc: check permissions earlier for /proc/*/wchan

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Message-ID: <20180217071923.GA16074@avx2>
Date:   Sat, 17 Feb 2018 10:19:24 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] proc: check permissions earlier for /proc/*/wchan

get_wchan() accesses stack page before permissions are checked,
let's not play this game.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/base.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -391,14 +391,17 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
 	unsigned long wchan;
 	char symname[KSYM_NAME_LEN];
 
-	wchan = get_wchan(task);
+	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+		goto print0;
 
-	if (wchan && ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)
-			&& !lookup_symbol_name(wchan, symname))
+	wchan = get_wchan(task);
+	if (wchan && !lookup_symbol_name(wchan, symname)) {
 		seq_printf(m, "%s", symname);
-	else
-		seq_putc(m, '0');
+		return 0;
+	}
 
+print0:
+	seq_putc(m, '0');
 	return 0;
 }
 #endif /* CONFIG_KALLSYMS */