This is a note to let you know that I've just added the patch titled netlink: fix locking around NETLINK_LIST_MEMBERSHIPS to the 4.2-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: netlink-fix-locking-around-netlink_list_memberships.patch and it can be found in the queue-4.2 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Nov 17 14:34:38 PST 2015 From: David Herrmann <dh.herrmann@xxxxxxxxx> Date: Wed, 21 Oct 2015 11:47:43 +0200 Subject: netlink: fix locking around NETLINK_LIST_MEMBERSHIPS From: David Herrmann <dh.herrmann@xxxxxxxxx> [ Upstream commit 47191d65b647af5eb5c82ede70ed4c24b1e93ef4 ] Currently, NETLINK_LIST_MEMBERSHIPS grabs the netlink table while copying the membership state to user-space. However, grabing the netlink table is effectively a write_lock_irq(), and as such we should not be triggering page-faults in the critical section. This can be easily reproduced by the following snippet: int s = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE); void *p = mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0); int r = getsockopt(s, 0x10e, 9, p, (void*)((char*)p + 4092)); This should work just fine, but currently triggers EFAULT and a possible WARN_ON below handle_mm_fault(). Fix this by reducing locking of NETLINK_LIST_MEMBERSHIPS to a read-side lock. The write-lock was overkill in the first place, and the read-lock allows page-faults just fine. Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/netlink/af_netlink.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2346,7 +2346,7 @@ static int netlink_getsockopt(struct soc int pos, idx, shift; err = 0; - netlink_table_grab(); + netlink_lock_table(); for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) { if (len - pos < sizeof(u32)) break; @@ -2361,7 +2361,7 @@ static int netlink_getsockopt(struct soc } if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen)) err = -EFAULT; - netlink_table_ungrab(); + netlink_unlock_table(); break; } default: Patches currently in stable-queue which might be from dh.herrmann@xxxxxxxxx are queue-4.2/netlink-fix-locking-around-netlink_list_memberships.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html