[Yaffs] Permission denied when non-root

[Luc Van Oostenryck]

Karl Olsen wrote:
> Hello all,
> 
> I am having a problem with switching to a non-root user on my
> AT91RM9200-based ARM system.  I am using Linux 2.6.10 with the AT91RM9200
> patch from http://maxim.org.za/AT91RM9200/2.6/ (fixed so that NAND support
> works) and the Yaffs patches by Frank Rowand, and a statically linked
> Busybox 1.00.  / is on a Yaffs partition.
> 
> # mount
> /dev/mtdblock1 on / type yaffs (rw,noatime)
> /dev/mtdblock0 on /boot type yaffs (ro,noatime)
> none on /proc type proc (rw,nodiratime)
> 
> Everything works fine when I'm root, and I can run Busybox commands and 
> read
> and write files.  But when I do a "su karl" it says:
> 
> / # su karl
> su: cannot run /bin/sh: Permission denied
> 
> /etc/passwd contains:
> root:x:0:0:root:/root:/bin/sh
> karl:x:500:100:KarlOlsen:/home/karl:/bin/sh
> 
> # ls -l -d /bin
> drwxr-xr-x    1 root     root          512 Jan  1 00:00 bin
> 
> /bin/sh is a symlink pointing to /bin/busybox:
> -rwxrwxrwx    1 root     root       438260 Jan  1 00:00 busybox
> 
> I have tried replacing /bin/sh in /etc/passwd with other commands, but I
> always get the Permission denied.  The Busybox source shows that it
> successfully changes identity to uid=500 and gid=100 and cd's to my home
> directory but fails at the execv() that tried to run /bin/sh.
> 
> I tried the same with an initrd with romfs, and with that, it worked.  But
> romfs doesn't seem to implement uid and gid for its files/directories.
> 
> Does anybody know if this problem can be related to Yaffs?  Does the Yaffs
> filesystem have (hidden) mount options that can deny execution for 
> non-root?

Yes and no, the default permissions for yaffs root directory is 0666 thus the directory is not accessible
for non root.
Changing the permissions of the root dir to 0777 (or better to 0755) cure the problem until the next reboot.

The following patch solve the problem permanently:
----
diff -r1.14 yportenv.h
102c102
< #define YAFFS_ROOT_MODE                               0666
---
> #define YAFFS_ROOT_MODE                               0755
----

> Regards,
> Karl Olsen


Luc Van Oostenryck