[PATCH 5.10 40/54] SUNRPC: Handle 0 length opaque XDR object data properly

Greg Kroah-Hartman
2021-02-11T15:36:09Z

From: Dave Wysochanski <dwysocha@redhat.com>

[ Upstream commit e4a7d1f7707eb44fd953a31dd59eff82009d879c ]

When handling an auth_gss downcall, it's possible to get 0-length
opaque object for the acceptor. In the case of a 0-length XDR
object, make sure simple_get_netobj() fills in dest->data = NULL,
and does not continue to kmemdup() which will set
dest->data = ZERO_SIZE_PTR for the acceptor.

The trace event code can handle NULL but not ZERO_SIZE_PTR for a
string, and so without this patch the rpcgss_context trace event
will crash the kernel as follows:

[ 162.887992] BUG: kernel NULL pointer dereference, address: 0000000000000010
[ 162.898693] #PF: supervisor read access in kernel mode
[ 162.900830] #PF: error_code(0x0000) - not-present page
[ 162.902940] PGD 0 P4D 0
[ 162.904027] Oops: 0000 [#1] SMP PTI
[ 162.905493] CPU: 4 PID: 4321 Comm: rpc.gssd Kdump: loaded Not tainted 5.10.0 #133
[ 162.908548] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[ 162.910978] RIP: 0010:strlen+0x0/0x20
[ 162.912505] Code: 48 89 f9 74 09 48 83 c1 01 80 39 00 75 f7 31 d2 44 0f b6 04 16 44 88 04 11 48 83 c2 01 45 84 c0 75 ee c3 0f 1f 80 00 00 00 00 <80> 3f 00 74 10 48 89 f8 48 83 c0 01 80 38 00 75 f7 48 29 f8 c3 31
[ 162.920101] RSP: 0018:ffffaec900c77d90 EFLAGS: 00010202
[ 162.922263] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000fffde697
[ 162.925158] RDX: 000000000000002f RSI: 0000000000000080 RDI: 0000000000000010
[ 162.928073] RBP: 0000000000000010 R08: 0000000000000e10 R09: 0000000000000000
[ 162.930976] R10: ffff8e698a590cb8 R11: 0000000000000001 R12: 0000000000000e10
[ 162.933883] R13: 00000000fffde697 R14: 000000010034d517 R15: 0000000000070028
[ 162.936777] FS: 00007f1e1eb93700(0000) GS:ffff8e6ab7d00000(0000) knlGS:0000000000000000
[ 162.940067] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 162.942417] CR2: 0000000000000010 CR3: 0000000104eba000 CR4: 00000000000406e0
[ 162.945300] Call Trace:
[ 162.946428] trace_event_raw_event_rpcgss_context+0x84/0x140 [auth_rpcgss]
[ 162.949308] ? __kmalloc_track_caller+0x35/0x5a0
[ 162.951224] ? gss_pipe_downcall+0x3a3/0x6a0 [auth_rpcgss]
[ 162.953484] gss_pipe_downcall+0x585/0x6a0 [auth_rpcgss]
[ 162.955953] rpc_pipe_write+0x58/0x70 [sunrpc]
[ 162.957849] vfs_write+0xcb/0x2c0
[ 162.959264] ksys_write+0x68/0xe0
[ 162.960706] do_syscall_64+0x33/0x40
[ 162.962238] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 162.964346] RIP: 0033:0x7f1e1f1e57df

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sunrpc/auth_gss/auth_gss_internal.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/sunrpc/auth_gss/auth_gss_internal.h b/net/sunrpc/auth_gss/auth_gss_internal.h
index c5603242b54bf..f6d9631bd9d00 100644
--- a/net/sunrpc/auth_gss/auth_gss_internal.h
+++ b/net/sunrpc/auth_gss/auth_gss_internal.h
@@ -34,9 +34,12 @@ simple_get_netobj(const void *p, const void *end, struct xdr_netobj *dest)
q = (const void *)((const char *)p + len);
if (unlikely(q > end || q < p))
return ERR_PTR(-EFAULT);
- dest->data = kmemdup(p, len, GFP_NOFS);
- if (unlikely(dest->data == NULL))
- return ERR_PTR(-ENOMEM);
+ if (len) {
+ dest->data = kmemdup(p, len, GFP_NOFS);
+ if (unlikely(dest->data == NULL))
+ return ERR_PTR(-ENOMEM);
+ } else
+ dest->data = NULL;
dest->len = len;
return q;
}
--
2.27.0