Re: [PATCH net v3] net: do not leave a dangling sk pointer, when socket creation fails

[Ignat Korchagin <ignat@cloudflare.com>]

On Wed, Jun 19, 2024 at 1:31 PM D. Wythe <alibuda@linux.alibaba.com> wrote:
>
>
>
> On 6/18/24 5:02 AM, Ignat Korchagin wrote:
> > It is possible to trigger a use-after-free by:
> >    * attaching an fentry probe to __sock_release() and the probe calling the
> >      bpf_get_socket_cookie() helper
> >    * running traceroute -I 1.1.1.1 on a freshly booted VM
> >
> > A KASAN enabled kernel will log something like below (decoded and stripped):
> > ==================================================================
> > BUG: KASAN: slab-use-after-free in __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > Read of size 8 at addr ffff888007110dd8 by task traceroute/299
> >
> > CPU: 2 PID: 299 Comm: traceroute Tainted: G            E      6.10.0-rc2+ #2
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> > Call Trace:
> >   <TASK>
> > dump_stack_lvl (lib/dump_stack.c:117 (discriminator 1))
> > print_report (mm/kasan/report.c:378 mm/kasan/report.c:488)
> > ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > kasan_report (mm/kasan/report.c:603)
> > ? __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > kasan_check_range (mm/kasan/generic.c:183 mm/kasan/generic.c:189)
> > __sock_gen_cookie (./arch/x86/include/asm/atomic64_64.h:15 ./include/linux/atomic/atomic-arch-fallback.h:2583 ./include/linux/atomic/atomic-instrumented.h:1611 net/core/sock_diag.c:29)
> > bpf_get_socket_ptr_cookie (./arch/x86/include/asm/preempt.h:94 ./include/linux/sock_diag.h:42 net/core/filter.c:5094 net/core/filter.c:5092)
> > bpf_prog_875642cf11f1d139___sock_release+0x6e/0x8e
> > bpf_trampoline_6442506592+0x47/0xaf
> > __sock_release (net/socket.c:652)
> > __sock_create (net/socket.c:1601)
> > ...
> > Allocated by task 299 on cpu 2 at 78.328492s:
> > kasan_save_stack (mm/kasan/common.c:48)
> > kasan_save_track (mm/kasan/common.c:68)
> > __kasan_slab_alloc (mm/kasan/common.c:312 mm/kasan/common.c:338)
> > kmem_cache_alloc_noprof (mm/slub.c:3941 mm/slub.c:4000 mm/slub.c:4007)
> > sk_prot_alloc (net/core/sock.c:2075)
> > sk_alloc (net/core/sock.c:2134)
> > inet_create (net/ipv4/af_inet.c:327 net/ipv4/af_inet.c:252)
> > __sock_create (net/socket.c:1572)
> > __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> > __x64_sys_socket (net/socket.c:1718)
> > do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> >
> > Freed by task 299 on cpu 2 at 78.328502s:
> > kasan_save_stack (mm/kasan/common.c:48)
> > kasan_save_track (mm/kasan/common.c:68)
> > kasan_save_free_info (mm/kasan/generic.c:582)
> > poison_slab_object (mm/kasan/common.c:242)
> > __kasan_slab_free (mm/kasan/common.c:256)
> > kmem_cache_free (mm/slub.c:4437 mm/slub.c:4511)
> > __sk_destruct (net/core/sock.c:2117 net/core/sock.c:2208)
> > inet_create (net/ipv4/af_inet.c:397 net/ipv4/af_inet.c:252)
> > __sock_create (net/socket.c:1572)
> > __sys_socket (net/socket.c:1660 net/socket.c:1644 net/socket.c:1706)
> > __x64_sys_socket (net/socket.c:1718)
> > do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
> > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> >
> > Fix this by clearing the struct socket reference in sk_common_release() to cover
> > all protocol families create functions, which may already attached the
> > reference to the sk object with sock_init_data().
> >
> > Fixes: c5dbb89fc2ac ("bpf: Expose bpf_get_socket_cookie to tracing programs")
> > Suggested-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
> > Cc: stable@vger.kernel.org
> > Link: https://lore.kernel.org/netdev/20240613194047.36478-1-kuniyu@amazon.com/T/
> > ---
> > Changes in v3:
> >    * re-added KASAN repro steps to the commit message (somehow stripped in v2)
> >    * stripped timestamps and thread id from the KASAN splat
> >    * removed comment from the code (commit message should be enough)
> >
> > Changes in v2:
> >    * moved the NULL-ing of the socket reference to sk_common_release() (as
> >      suggested by Kuniyuki Iwashima)
> >    * trimmed down the KASAN report in the commit message to show only relevant
> >      info
> >
> >   net/core/sock.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 8629f9aecf91..100e975073ca 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -3742,6 +3742,9 @@ void sk_common_release(struct sock *sk)
> >
> >       sk->sk_prot->unhash(sk);
> >
> > +     if (sk->sk_socket)
> > +             sk->sk_socket->sk = NULL;
> > +
> >       /*
> >        * In this point socket cannot receive new packets, but it is possible
> >        * that some packets are in flight because some CPU runs receiver and
>
> Reviewed-by: D. Wythe <alibuda@linux.alibaba.com>
>
>
> A small tip:
>
> It seems that you might have missed CCing some maintainers, using
> scripts/get_maintainer.pl "Your patch" can help you avoid this issue
> again.

Thanks. I did scripts/get_maintainer.pl <file I'm modifying>. Not sure
if it is different.

>
> D. Wythe
>
>
>