linux-kernel - [PATCH] powerpc/signal32: Fix erroneous SIGSEGV on RT signal return

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Message-Id: <a29aadc54c93bcbf069a83615fa102ca0f59c3ae.1619185912.git.christophe.leroy@csgroup.eu>
Date:   Fri, 23 Apr 2021 13:52:10 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/signal32: Fix erroneous SIGSEGV on RT signal return

Return of user_read_access_begin() is tested the wrong way,
leading to a SIGSEGV when the user address is valid and likely
an Oops when the user address is bad.

Fix the test.

Fixes: 887f3ceb51cd ("powerpc/signal32: Convert do_setcontext[_tm]() to user access block")
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/signal_32.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index fc41c58f0cbb..8f05ed0da292 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -967,7 +967,7 @@ static int do_setcontext(struct ucontext __user *ucp, struct pt_regs *regs, int
 	sigset_t set;
 	struct mcontext __user *mcp;
 
-	if (user_read_access_begin(ucp, sizeof(*ucp)))
+	if (!user_read_access_begin(ucp, sizeof(*ucp)))
 		return -EFAULT;
 
 	unsafe_get_sigset_t(&set, &ucp->uc_sigmask, failed);
@@ -1005,7 +1005,7 @@ static int do_setcontext_tm(struct ucontext __user *ucp,
 	u32 cmcp;
 	u32 tm_cmcp;
 
-	if (user_read_access_begin(ucp, sizeof(*ucp)))
+	if (!user_read_access_begin(ucp, sizeof(*ucp)))
 		return -EFAULT;
 
 	unsafe_get_sigset_t(&set, &ucp->uc_sigmask, failed);
-- 
2.25.0