[PATCH 5.4 114/215] exec: Fix NOMMU linux_binprm::exec in transfer_args_to_stack()

Greg Kroah-Hartman
2024-04-11T10:21:31Z

From: Max Filippov <jcmvbkbc@gmail.com>

commit 2aea94ac14d1e0a8ae9e34febebe208213ba72f7 upstream.

In NOMMU kernel the value of linux_binprm::p is the offset inside the
temporary program arguments array maintained in separate pages in the
linux_binprm::page. linux_binprm::exec being a copy of linux_binprm::p
thus must be adjusted when that array is copied to the user stack.
Without that adjustment the value passed by the NOMMU kernel to the ELF
program in the AT_EXECFN entry of the aux array doesn't make any sense
and it may break programs that try to access memory pointed to by that
entry.

Adjust linux_binprm::exec before the successful return from the
transfer_args_to_stack().

Cc: <stable@vger.kernel.org>
Fixes: b6a2fea39318 ("mm: variable length argument support")
Fixes: 5edc2a5123a7 ("binfmt_elf_fdpic: wire up AT_EXECFD, AT_EXECFN, AT_SECURE")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Link: https://lore.kernel.org/r/20240320182607.1472887-1-jcmvbkbc@gmail.com
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/exec.c | 1 +
1 file changed, 1 insertion(+)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -836,6 +836,7 @@ int transfer_args_to_stack(struct linux_
goto out;
}

+ bprm->exec += *sp_location - MAX_ARG_PAGES * PAGE_SIZE;
*sp_location = sp;