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syslog: distinguish between /proc/kmsg and syscalls

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This allows the LSM to distinguish between syslog functions originating
from /proc/kmsg access and direct syscalls.  By default, the commoncaps
will now no longer require CAP_SYS_ADMIN to read an opened /proc/kmsg
file descriptor.  For example the kernel syslog reader can now drop
privileges after opening /proc/kmsg, instead of staying privileged with
CAP_SYS_ADMIN.  MAC systems that implement security_syslog have unchanged
behavior.

Signed-off-by: Kees Cook <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Acked-by: John Johansen <[email protected]>
Signed-off-by: James Morris <[email protected]>
This commit is contained in:
Kees Cook 2010-02-03 15:36:43 -08:00 • committed by James Morris
commit 002345925e
8 changed files with 59 additions and 22 deletions
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7
security/commoncap.c
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@ -27,6 +27,7 @@
#include <linux/sched.h>
#include <linux/prctl.h>
#include <linux/securebits.h>
#include <linux/syslog.h>
/*
* If a non-root user executes a setuid-root binary in
@ -888,12 +889,16 @@ error:
/**
* cap_syslog - Determine whether syslog function is permitted
* @type: Function requested
* @from_file: Whether this request came from an open file (i.e. /proc)
*
* Determine whether the current process is permitted to use a particular
* syslog function, returning 0 if permission is granted, -ve if not.
*/
int cap_syslog(int type)
int cap_syslog(int type, bool from_file)
{
/* /proc/kmsg can open be opened by CAP_SYS_ADMIN */
if (type != 1 && from_file)
return 0;
if ((type != 3 && type != 10) && !capable(CAP_SYS_ADMIN))
return -EPERM;
return 0;