linux-kernel - [PATCH v2] vsprintf: kptr_restrict is okay in IRQ when 2

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Message-Id: <1454709783-17385-1-git-send-email-Jason@zx2c4.com>
Date:	Fri,  5 Feb 2016 23:03:03 +0100
From:	"Jason A. Donenfeld" <Jason@...c4.com>
To:	keescook@...omium.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Cc:	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH v2] vsprintf: kptr_restrict is okay in IRQ when 2

The kptr_restrict flag, when set to 1, only prints the kernel
address when the user has CAP_SYSLOG. When it is set to 2, the
kernel address is always printed as zero. When set to 1, this
needs to check whether or not we're in IRQ. However, when set to
2, this check is unneccessary, and produces confusing results
in dmesg. Thus, only make sure we're not in IRQ when mode 1 is
used, but not mode 2.

Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 lib/vsprintf.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 80d8ce5..ee1e24e 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1605,22 +1605,23 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return buf;
 		}
 	case 'K':
-		/*
-		 * %pK cannot be used in IRQ context because its test
-		 * for CAP_SYSLOG would be meaningless.
-		 */
-		if (kptr_restrict && (in_irq() || in_serving_softirq() ||
-				      in_nmi())) {
-			if (spec.field_width == -1)
-				spec.field_width = default_width;
-			return string(buf, end, "pK-error", spec);
-		}
-
 		switch (kptr_restrict) {
 		case 0:
 			/* Always print %pK values */
 			break;
 		case 1: {
+			const struct cred *cred;
+
+			/*
+			 * kptr_restrict==2 cannot be used in IRQ context because
+			 * its test for CAP_SYSLOG would be meaningless.
+			 */
+			if (in_irq() || in_serving_softirq() || in_nmi()) {
+				if (spec.field_width == -1)
+					spec.field_width = default_width;
+				return string(buf, end, "pK-error", spec);
+			}
+
 			/*
 			 * Only print the real pointer value if the current
 			 * process has CAP_SYSLOG and is running with the
@@ -1630,8 +1631,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			 * leak pointer values if a binary opens a file using
 			 * %pK and then elevates privileges before reading it.
 			 */
-			const struct cred *cred = current_cred();
-
+			cred = current_cred();
 			if (!has_capability_noaudit(current, CAP_SYSLOG) ||
 			    !uid_eq(cred->euid, cred->uid) ||
 			    !gid_eq(cred->egid, cred->gid))
-- 
2.7.0