From:   "H.J. Lu" <hjl.tools@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH] fs/binfmt_elf.c: disallow zero entry point address
Date:   Sat, 11 Dec 2021 09:34:47 -0800
Message-Id: <20211211173447.4155374-1-hjl.tools@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

According to gABI, the entry point address in the ELF header gives the
virtual address to which the system first transfers control, thus
starting the process.  If the file has no associated entry point, this
member holds zero.  Update the ELF loader to disallow an ELF binary
with zero entry point address.  This fixes:

https://bugzilla.kernel.org/show_bug.cgi?id=215303

Tested by booting Fedora 35 and running a shared library with zero entry
point address:

$ readelf -h load.so | grep "Entry point address:"
  Entry point address:               0x0
$ ./load.so
bash: ./load.so: cannot execute binary file: Exec format error
$

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
 fs/binfmt_elf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index bd78587194dc..bb427c97dc02 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -850,6 +850,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
 
 	if (elf_ex->e_type != ET_EXEC && elf_ex->e_type != ET_DYN)
 		goto out;
+	if (elf_ex->e_entry == 0)
+		goto out;
 	if (!elf_check_arch(elf_ex))
 		goto out;
 	if (elf_check_fdpic(elf_ex))
-- 
2.33.1