From 47191d65b647af5eb5c82ede70ed4c24b1e93ef4 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Wed, 21 Oct 2015 11:47:43 +0200 Subject: [PATCH] netlink: fix locking around NETLINK_LIST_MEMBERSHIPS 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 Signed-off-by: David Herrmann Signed-off-by: David S. Miller --- net/netlink/af_netlink.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 0a49a8c7c564..fafe33bdb619 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -2371,7 +2371,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname, 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; @@ -2386,7 +2386,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname, } if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen)) err = -EFAULT; - netlink_table_ungrab(); + netlink_unlock_table(); break; } case NETLINK_CAP_ACK: