On Mon, Oct 17, 2011 at 6:49 PM, Philip Anil-QBW348 <anil.philip@motorolasolutions.com> wrote:
-----Original Message----- From: Daniel Baluta [mailto:daniel.baluta@gmail.com] Sent: Saturday, October 15, 2011 3:34 AM To: Philip Anil-QBW348 Cc: kernelnewbies@kernelnewbies.org Subject: Re: Getting 'bad file number' error writing to device driver
On Sat, Oct 15, 2011 at 2:42 AM, Philip Anil-QBW348 <anil.philip@motorolasolutions.com> wrote:
I am calling the driver from an Android program (OMAP4/Blaze). It calls a c++ program via JNI which then calls the device driver. Someone suggested it might be a permissions problem - the program is running in user mode.
on Blaze board, /system/bin # ls -l -rwxrwxrwx system system 7636 2011-09-30 03:53 mydriver
Will strace still be useful? In general, in Linux, how does one enable a user program to call a custom device driver?
Please don't top post! :)
strace will be useful to check the parameters for open, write system calls.
EBADF fd is not a valid file descriptor or is not open for writing. Ok, so either open fails, or you don't have the permission to write into /dev/mydriver file.
------ I apologize for 'top-posting' (I did not know that was undesirable - most email clients and also Google newsgroups put one's reply at the top.). Yes, the /dev/mydriver had permissions 600. I did a chmod to 666 and it worked. I am performing security testing and want to see if a program running in user mode can elevate its privileges to call the device driver which has permissions 600. Any ideas how it can? Anil
Maybe setuid bit can help you ([1]). When this bit is set, a certain program can run with the privileges of its owner. thanks, Daniel. [1] http://en.wikipedia.org/wiki/Setuid