[patch 063/140] proc: check permissions earlier for /proc/*/wchan

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From: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Subject: proc: check permissions earlier for /proc/*/wchan

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

Link: http://lkml.kernel.org/r/20180217071923.GA16074@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

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

diff -puN fs/proc/base.c~proc-check-permissions-earlier-for-proc-wchan fs/proc/base.c
--- a/fs/proc/base.c~proc-check-permissions-earlier-for-proc-wchan
+++ a/fs/proc/base.c
@@ -388,14 +388,17 @@ static int proc_pid_wchan(struct seq_fil
 	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 */
_
--
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