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Subject[PATCH 3.19.y-ckt 47/47] KEYS: Fix keyring ref leak in join_session_keyring()
Date
3.19.8-ckt15 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Yevgeny Pats <yevgeny@perception-point.io>

commit 23567fd052a9abb6d67fe8e7a9ccdd9800a540f2 upstream.

This fixes CVE-2016-0728.

If a thread is asked to join as a session keyring the keyring that's already
set as its session, we leak a keyring reference.

This can be tested with the following program:

#include <stddef.h>
#include <stdio.h>
#include <sys/types.h>
#include <keyutils.h>

int main(int argc, const char *argv[])
{
int i = 0;
key_serial_t serial;

serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
"leaked-keyring");
if (serial < 0) {
perror("keyctl");
return -1;
}

if (keyctl(KEYCTL_SETPERM, serial,
KEY_POS_ALL | KEY_USR_ALL) < 0) {
perror("keyctl");
return -1;
}

for (i = 0; i < 100; i++) {
serial = keyctl(KEYCTL_JOIN_SESSION_KEYRING,
"leaked-keyring");
if (serial < 0) {
perror("keyctl");
return -1;
}
}

return 0;
}

If, after the program has run, there something like the following line in
/proc/keys:

3f3d898f I--Q--- 100 perm 3f3f0000 0 0 keyring leaked-keyring: empty

with a usage count of 100 * the number of times the program has been run,
then the kernel is malfunctioning. If leaked-keyring has zero usages or
has been garbage collected, then the problem is fixed.

Reported-by: Yevgeny Pats <yevgeny@perception-point.io>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
security/keys/process_keys.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index bd536cb..db91639 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -794,6 +794,7 @@ long join_session_keyring(const char *name)
ret = PTR_ERR(keyring);
goto error2;
} else if (keyring == new->session_keyring) {
+ key_put(keyring);
ret = 0;
goto error2;
}
--
1.9.1
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