[apparmor] [RFC] libapparmor: Don't expose a value-result param in aa_getpeercon_raw()

Seth Arnold seth.arnold at canonical.com
Tue Jun 25 21:58:49 UTC 2013

On Tue, Jun 25, 2013 at 01:19:17PM -0700, Tyler Hicks wrote:
> Unify aa_getprocattr_raw() and aa_getpeercon_raw() function prototypes
> by hiding the len value-result parameter.
> Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
> Cc: Seth Arnold <seth.arnold at canonical.com>
> Cc: John Johansen <john.johansen at canonical.com>
> ---
> Code speaks louder and more clearly than my poor explanation, so here's an RFC
> patch on the idea.
> I think that this addresses Seth's distaste of the len parameter. It makes the
> libapparmor API a little more predictable, but hides a useful feature of the
> getsockopt() syscall which will make external callers guess at buffer
> reallocation sizes (but they already do that with aa_getprocattr_raw()).
> I'm fine with or without this patch, as I don't expect (m)any applications to
> use aa_getpeercon_raw().

Hrm, I thought I was going to like this more than I did. I thought
unifying the interface to match aa_getprocattr_raw() was going to be a
good idea, but it just doesn't feel very satisfying.

Incidentally, because I also failed to describe what I thought would
make a good patch, here's what I thought would work:

diff -Naurp libapparmor.orig/src/kernel_interface.c libapparmor/src/kernel_interface.c
--- libapparmor.orig/src/kernel_interface.c	2012-12-06 18:33:20.000000000 -0800
+++ libapparmor/src/kernel_interface.c	2013-06-25 14:33:45.000000000 -0700
@@ -554,7 +554,7 @@ int aa_getcon(char **con, char **mode)
  * @con: pointer to buffer to store confinement string
  * @size: initially contains size of the buffer, returns size of data read
- * Returns: length of confinement data including null termination or -1 on error
+ * Returns: 0 on success or -1 on error
  *          if errno == ERANGE then @size will hold the size needed
 int aa_getpeercon_raw(int fd, char *buffer, int *size)

BUT, enough other routines return the length via return that having this
one be different would also be annoying.

I assume it's too late to add a & to the aa_getprocattr_raw() len
parameter? :)

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