Commit 47191d65 authored by David Herrmann's avatar David Herrmann Committed by David S. Miller

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: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarDavid Herrmann <dh.herrmann@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 34e45ad9
...@@ -2371,7 +2371,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname, ...@@ -2371,7 +2371,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname,
int pos, idx, shift; int pos, idx, shift;
err = 0; err = 0;
netlink_table_grab(); netlink_lock_table();
for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) { for (pos = 0; pos * 8 < nlk->ngroups; pos += sizeof(u32)) {
if (len - pos < sizeof(u32)) if (len - pos < sizeof(u32))
break; break;
...@@ -2386,7 +2386,7 @@ static int netlink_getsockopt(struct socket *sock, int level, int optname, ...@@ -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)) if (put_user(ALIGN(nlk->ngroups / 8, sizeof(u32)), optlen))
err = -EFAULT; err = -EFAULT;
netlink_table_ungrab(); netlink_unlock_table();
break; break;
} }
case NETLINK_CAP_ACK: case NETLINK_CAP_ACK:
......
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