[PATCH AUTOSEL 4.19 06/14] ELF: fix kernel.randomize_va_space double read

Sasha Levin
2024-08-01T00:40:54Z

From: Alexey Dobriyan <adobriyan@gmail.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@gmail.com>
Link: https://lore.kernel.org/r/3329905c-7eb8-400a-8f0a-d87cff979b5b@p183
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 c41c568ad1b8a..af8830878fa0b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -876,7 +876,8 @@ 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);
@@ -1136,7 +1137,7 @@ 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