[PATCH] module: propagate error in modules_open()

[Leon Yu]

otherwise kernel can oops later in seq_release() due to dereferencing null
file->private_data which is only set if seq_open() succeeds.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
IP: seq_release+0xc/0x30
Call Trace:
 close_pdeo+0x37/0xd0
 proc_reg_release+0x5d/0x60
 __fput+0x9d/0x1d0
 ____fput+0x9/0x10
 task_work_run+0x75/0x90
 do_exit+0x252/0xa00
 do_group_exit+0x36/0xb0
 SyS_exit_group+0xf/0x10

Fixes: 516fb7f2e73d ("/proc/module: use the same logic as /proc/kallsyms for address exposure")
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # 4.15+
Signed-off-by: Leon Yu <chianglungyu@xxxxxxxxx>
---
 kernel/module.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
index ad2d420024f6..e42764acedb4 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4228,7 +4228,7 @@ static int modules_open(struct inode *inode, struct file *file)
                m->private = kallsyms_show_value() ? NULL : (void *)8ul;
        }

-       return 0;
+       return err;
 }

 static const struct file_operations proc_modules_operations = {
--
2.16.2