Messages in this thread | | | From | shankarapailoor <> | Date | Tue, 5 Jun 2018 19:19:08 -0700 | Subject | Re: general protection fault in sockfs_setattr |
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Hi Cong,
I added that check and it seems to stop the crash. Like you said, I don't see where the reference count for the file is increased. The inode lock also seems to be held during this call.
Regards, Shankara
On Tue, Jun 5, 2018 at 12:14 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote: > On Mon, Jun 4, 2018 at 9:53 PM, shankarapailoor > <shankarapailoor@gmail.com> wrote: >> Hi, >> >> I have been fuzzing Linux 4.17-rc7 with Syzkaller and found the >> following crash: https://pastebin.com/ixX3RB9j >> >> Syzkaller isolated the cause of the bug to the following program: >> >> socketpair$unix(0x1, 0x1, 0x0, >> &(0x7f0000000000)={<r0=>0xffffffffffffffff, <r1=>0xffffffffffffffff}) >> getresuid(&(0x7f0000000080)=<r2=>0x0, &(0x7f00000000c0), >> &(0x7f0000000700))r3 = getegid() >> fchownat(r0, &(0x7f0000000040)='\x00', r2, r3, 0x1000) >> dup3(r1, r0, 0x80000) >> >> >> The problematic area appears to be here: >> >> static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr) >> { >> int err = simple_setattr(dentry, iattr); >> >> if (!err && (iattr->ia_valid & ATTR_UID)) { >> struct socket *sock = SOCKET_I(d_inode(dentry)); >> >> sock->sk->sk_uid = iattr->ia_uid; //KASAN GPF >> } >> return err; >> } >> >> If dup3 is called concurrently with fchownat then can sock->sk be NULL? > > Although dup3() implies a close(), fd is refcnt'ted, if dup3() runs > concurrently with fchownat() it should not be closed until whoever > the last closes it. > > Or maybe fchownat() doesn't even hold refcnt of fd, since it aims > to change the file backed. > > > Not sure if the following is sufficient, inode might need to be protected > with some lock... > > diff --git a/net/socket.c b/net/socket.c > index f10f1d947c78..6294b4b3132e 100644 > --- a/net/socket.c > +++ b/net/socket.c > @@ -537,7 +537,10 @@ static int sockfs_setattr(struct dentry *dentry, > struct iattr *iattr) > if (!err && (iattr->ia_valid & ATTR_UID)) { > struct socket *sock = SOCKET_I(d_inode(dentry)); > > - sock->sk->sk_uid = iattr->ia_uid; > + if (sock->sk) > + sock->sk->sk_uid = iattr->ia_uid; > + else > + err = -ENOENT; > } > > return err;
-- Regards, Shankara Pailoor
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