Bug at kernel/cred.c +432

[rishabhb]

Hi Miklos

In 4.19 kernel when we write to a file that doesn't exist we see the
following stack:
[  377.382745]  ovl_create_or_link+0xac/0x710
[  377.382745]  ovl_create_object+0xb8/0x110
[  377.382745]  ovl_create+0x34/0x40
[  377.382745]  path_openat+0xd44/0x15a8
[  377.382745]  do_filp_open+0x80/0x128
[  377.382745]  do_sys_open+0x140/0x250
[  377.382745]  __arm64_sys_openat+0x2c/0x38

If the override_cred flag = off, the ovl_override_cred and 
ovl_revert_cred just returns NULL.
But there is another override_cred in between these two functions;
		put_cred(override_creds(override_cred));
		put_cred(override_cred);

This will override the credentials permanently as there is no 
corresponding revert_cred associated.
So whenever we do commit_creds for this task, we see a BUG_ON at 
kernel/cred.c +443.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/cred.c#n443

Should this override_cred be changed to ovl_override_cred to maintain 
consistency and avoid this
BUG_ON?


Thanks,
Rishabh