[PATCH] sunrpc/auth_gss: NULL pointer deref in gss_pipe_release()

["Alex Polvi" <polvi@google.com>]

Proposed (trivial) patch to fix a NULL pointer deref in
gss_pipe_release(). While this does seem to fix the problem, I'm not
entirely sure it is the correct place to handle the NULL pointer.

Included below is the script I used to recreate the problem, the oops,
and the patch.

polvi@return:~/sysops/experimental/polvi$ cat oopsmynfs.sh
#!/bin/bash

cd / # make sure we are not in the dir

PROG=${0##*/}

function usage {
 cat <<EOF
usage: $PROG /nfs/path/

will oops sunrpc using the nfs host that serves /nfs/path/
EOF
 exit 1
}

DIR=$1

[ -d "$DIR" ] || usage

sudo umount $DIR 2> /dev/null # just house-keeping...

sudo mount -o sec=krb5 randomfiler:/vol/to/some/share $DIR # must use krb5

# with out this ls the cd below will say permission denied and not
hang after the
# nfs server has been turned off. It has something to do with stat64
returning EACCES
ls $DIR > /dev/null

echo "Make the nfs server unusable by the client (turn off nfs, iptables, etc)."
read -p "press enter when ready"

# if the echo is hit, this script failed to oops sunrpc
(cd $DIR/. ;  echo "will not cause an oops") & # this should hang

sudo umount -l $DIR

echo "Turn the nfs server back on and watch for the oops.  Should not
take more then 10s"


[  204.385339] net/sunrpc/rpc_pipe.c: rpc_lookup_parent failed to find
path /nfs/clnt4/krb5
[  204.385427] BUG: unable to handle kernel NULL pointer dereference
at virtual address 0000006c
[  204.385554]  printing eip:
[  204.385595] c01d2322
[  204.385678] *pde = 00000000
[  204.385719] Oops: 0000 [#1]
[  204.385781] SMP
[  204.385875] Modules linked in: des binfmt_misc autofs4 video button
battery ac nfs lockd af_packet sg sr_mod pcspkr rtc psm


                                  ouse mousedev ide_disk ide_cd cdrom
rpcsec_gss_krb5 auth_rpcgss sunrpc ext3 jbd mbcache thermal processor
fan tg3 sd_mod ide_g


eneric ata_piix libata scsi_mod generic ide_core unix
[  204.387417] CPU:    0
[  204.387418] EIP:    0060:[<c01d2322>]    Not tainted VLI
[  204.387419] EFLAGS: 00010292   (2.6.18-rc2-git #1)
[  204.387538] EIP is at _raw_spin_lock+0x12/0x170
[  204.387578] eax: 00000068   ebx: 00000068   ecx: f7157d3c   edx: f7157d3c
[  204.387621] esi: 00000068   edi: 00000000   ebp: f7157d00   esp: f7157cdc
[  204.387664] ds: 007b   es: 007b   ss: 0068
[  204.387704] Process oopsmynfs.sh (pid: 6114, ti=f7156000
task=dffb5aa0 task.ti=f7156000)
[  204.387748] Stack: dffb5aa0 f7157d1c c029ee7d f7157cfc f7156000
f7156000 f73acd00 00000068
[  204.388040]        00000000 f7157d0c c029ff7e 00000068 f7157d24
f88d82cf f73acd00 f73acd00
[  204.388332]        f73acecc f88e1554 f7157d50 f8cbd6a9 f73acd00
f7288460 f73acd80 f73acd70
[  204.388625] Call Trace:
[  204.388868]  [<c029ff7e>] _spin_lock+0xe/0x10
[  204.388997]  [<f88d82cf>] gss_pipe_release+0x1f/0x70 [auth_rpcgss]
[  204.389075]  [<f8cbd6a9>] rpc_close_pipes+0xe9/0x130 [sunrpc]
[  204.389173]  [<f8cbd91f>] rpc_depopulate+0xff/0x140 [sunrpc]
[  204.389267]  [<f8cbda8d>] rpc_rmdir+0x6d/0xa0 [sunrpc]
[  204.389360]  [<f8cac95e>] rpc_destroy_client+0xde/0x110 [sunrpc]
[  204.389443]  [<f8cac8e1>] rpc_destroy_client+0x61/0x110 [sunrpc]
[  204.389524]  [<f8cacab7>] rpc_shutdown_client+0xb7/0x120 [sunrpc]
[  204.389605]  [<f8b2643b>] nfs_kill_super+0x3b/0x90 [nfs]
[  204.389692]  [<c016e2c1>] deactivate_super+0x81/0xa0
[  204.389858]  [<c0185522>] mntput_no_expire+0x52/0x90
[  204.390039]  [<c01770da>] path_release+0x2a/0x30
[  204.390211]  [<c01715cb>] vfs_stat_fd+0x4b/0x60
[  204.390378]  [<c0171600>] vfs_stat+0x20/0x30
[  204.390545]  [<c0171fc9>] sys_stat64+0x19/0x30
[  204.390712]  [<c0102fb1>] sysenter_past_esp+0x56/0x79
[  204.390787]  [<b7fff410>] 0xb7fff410
[  204.390854] Code: 2b c0 89 f8 e8 00 fe ff ff e9 14 ff ff ff 8d 74
26 00 8d bc 27 00 00 00 00 55 89 e5 83 ec 24 89 5d f4 8b


                                    5d 08 89 75 f8 89 7d fc <81> 7b
04 ad 4e ad de 75 4c 89 e0 25 00 e0 ff ff 8b 00 39 43 0c
[  204.392662] EIP: [<c01d2322>] _raw_spin_lock+0x12/0x170 SS:ESP 0068:f7157cdc

Signed-off-by: Alex Polvi <polvi@google.com>
---
diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 4a9aa93..2db3bd1 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -607,6 +607,9 @@ gss_pipe_release(struct inode *inode)
      struct rpc_auth *auth;
      struct gss_auth *gss_auth;

+       if (rpci->ops == NULL)
+               return;
+
      clnt = rpci->private;
      auth = clnt->cl_auth;
      gss_auth = container_of(auth, struct gss_auth, rpc_auth);
-
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