Reading /proc/sys/kernel/cap-bound requires CAP_SYS_MODULE. (see
proc_dointvec_bset in kernel/sysctl.c)
sysctl appears to drive all over proc reading everything it can get it's
hands on and is complaining when it is being denied access to read
cap-bound. Clearly writing to cap-bound should be a sensitive operation
but requiring CAP_SYS_MODULE to read cap-bound seems a bit to strong. I
believe the information could with reasonable certainty be obtained by
looking at a bunch of the output of /proc/pid/status which has very low
security protection, so at best we are just getting a little obfuscation
of information.
Currently SELinux policy has to 'dontaudit' capability checks for
CAP_SYS_MODULE for things like sysctl which just want to read cap-bound.
In doing so we also as a by product have to hide warnings of potential
exploits such as if at some time that sysctl actually tried to load a
module. I wondered if anyone would have a problem opening cap-bound up
to read from anyone? Possibly with something like the patch below?
-Eric
kernel/sysctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6-upstream/kernel/sysctl.c.cap.sys.module
+++ linux-2.6-upstream/kernel/sysctl.c
@@ -2020,7 +2020,7 @@ int proc_dointvec_bset(ctl_table *table,
{
int op;
- if (!capable(CAP_SYS_MODULE)) {
+ if (write && !capable(CAP_SYS_MODULE)) {
return -EPERM;
}
-
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