Fix for unassigned errno in xenstored_core.c

[Magnus Carlsson <magnus@galois.com>]

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Dear all,

In certain cases, when a client doesn't have enough permissions, the
errno variable is not set in xenstored_core.c before its value is
reported back.  As a result, the client can learn about the errno of the
last failed request to xenstored (which could have come from another
client).  (An unintended information channel! :-)

Attached is a patch that I believe fixes the problem.  Also included are
a couple of test cases that demonstrate the problem.

Cheers,
Magnus


[-- Attachment #2: xenstored_core.patch --]
[-- Type: text/x-patch, Size: 690 bytes --]

*** xenstore/xenstored_core.c	Sun Apr  9 15:05:54 2006
--- xs/xenstored_core.c	Fri Nov  3 15:57:13 2006
***************
*** 555,562 ****
  	/* If we don't have permission, we don't have node. */
  	if (node) {
  		if ((perm_for_conn(conn, node->perms, node->num_perms) & perm)
! 		    != perm)
  			node = NULL;
  	}
  	/* Clean up errno if they weren't supposed to know. */
  	if (!node) 
--- 555,564 ----
  	/* If we don't have permission, we don't have node. */
  	if (node) {
  		if ((perm_for_conn(conn, node->perms, node->num_perms) & perm)
! 		    != perm) {
! 			errno = EACCES;
  			node = NULL;
+ 		}
  	}
  	/* Clean up errno if they weren't supposed to know. */
  	if (!node) 


[-- Attachment #3: 99permissions.test --]
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write /a/b v
setperm /a 1 READ
setperm /a/b 1 NONE

expect read failed: No such file or directory
read /nonexistent

setid 2

# this should presumably fail with EACCES, but fails with previous error instead
expect read failed: Permission denied
read /a/b

[-- Attachment #4: 99permissions2.test --]
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write /a/b v
setperm /a 1 READ
setperm /a/b 1 NONE

expect read failed: Invalid argument
read //

setid 2

# this should presumably fail with EACCES, but fails with previous error instead
expect read failed: Permission denied
read /a/b

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