linux-kernel - [PATCH AUTOSEL 5.4 12/22] ELF: fix kernel.randomize_va

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Message-ID: <20240801003918.3939431-12-sashal@kernel.org>
Date: Wed, 31 Jul 2024 20:38:41 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Alexey Dobriyan <adobriyan@...il.com>,
	Kees Cook <kees@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	viro@...iv.linux.org.uk,
	brauner@...nel.org,
	linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH AUTOSEL 5.4 12/22] ELF: fix kernel.randomize_va_space double read

From: Alexey Dobriyan <adobriyan@...il.com>

[ Upstream commit 2a97388a807b6ab5538aa8f8537b2463c6988bd2 ]

ELF loader uses "randomize_va_space" twice. It is sysctl and can change
at any moment, so 2 loads could see 2 different values in theory with
unpredictable consequences.

Issue exactly one load for consistent value across one exec.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
Link: https://lore.kernel.org/r/3329905c-7eb8-400a-8f0a-d87cff979b5b@p183
Signed-off-by: Kees Cook <kees@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/binfmt_elf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 72cd871544ac0..33c323a2ccb19 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -854,7 +854,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	if (elf_read_implies_exec(loc->elf_ex, executable_stack))
 		current->personality |= READ_IMPLIES_EXEC;
 
-	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
+	const int snapshot_randomize_va_space = READ_ONCE(randomize_va_space);
+	if (!(current->personality & ADDR_NO_RANDOMIZE) && snapshot_randomize_va_space)
 		current->flags |= PF_RANDOMIZE;
 
 	setup_new_exec(bprm);
@@ -1106,7 +1107,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	current->mm->end_data = end_data;
 	current->mm->start_stack = bprm->p;
 
-	if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1)) {
+	if ((current->flags & PF_RANDOMIZE) && (snapshot_randomize_va_space > 1)) {
 		/*
 		 * For architectures with ELF randomization, when executing
 		 * a loader directly (i.e. no interpreter listed in ELF
-- 
2.43.0