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fs/9p: avoid accessing utsname after namespace has been torn down

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During trinity fuzzing in a kvmtool guest, I stumbled across the
following:

Unable to handle kernel NULL pointer dereference at virtual address 00000004
PC is at v9fs_file_do_lock+0xc8/0x1a0
LR is at v9fs_file_do_lock+0x48/0x1a0
[<c01e2ed0>] (v9fs_file_do_lock+0xc8/0x1a0) from [<c0119154>] (locks_remove_flock+0x8c/0x124)
[<c0119154>] (locks_remove_flock+0x8c/0x124) from [<c00d9bf0>] (__fput+0x58/0x1e4)
[<c00d9bf0>] (__fput+0x58/0x1e4) from [<c0044340>] (task_work_run+0xac/0xe8)
[<c0044340>] (task_work_run+0xac/0xe8) from [<c002e36c>] (do_exit+0x6bc/0x8d8)
[<c002e36c>] (do_exit+0x6bc/0x8d8) from [<c002e674>] (do_group_exit+0x3c/0xb0)
[<c002e674>] (do_group_exit+0x3c/0xb0) from [<c002e6f8>] (__wake_up_parent+0x0/0x18)

I believe this is due to an attempt to access utsname()->nodename, after
exit_task_namespaces() has been called, leaving current->nsproxy->uts_ns
as NULL and causing the above dereference.

A similar issue was fixed for lockd in 9a1b6bf818 ("LOCKD: Don't call
utsname()->nodename from nlmclnt_setlockargs"), so this patch attempts
something similar for 9pfs.

Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
This commit is contained in:
Will Deacon 2013-08-21 18:24:47 +01:00 committed by Eric Van Hensbergen
parent e0d6cb9cd3
commit 50192abe02
3 changed files with 12 additions and 2 deletions
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4
fs/9p/vfs_file.c
View file

@ -183,7 +183,7 @@ static int v9fs_file_do_lock(struct file *filp, int cmd, struct file_lock *fl)
else
flock.length = fl->fl_end - fl->fl_start + 1;
flock.proc_id = fl->fl_pid;
flock.client_id = utsname()->nodename;
flock.client_id = fid->clnt->name;
if (IS_SETLKW(cmd))
flock.flags = P9_LOCK_FLAGS_BLOCK;
@ -260,7 +260,7 @@ static int v9fs_file_getlock(struct file *filp, struct file_lock *fl)
else
glock.length = fl->fl_end - fl->fl_start + 1;
glock.proc_id = fl->fl_pid;
glock.client_id = utsname()->nodename;
glock.client_id = fid->clnt->name;
res = p9_client_getlock_dotl(fid, &glock);
if (res < 0)

5
include/net/9p/client.h
View file

@ -26,6 +26,8 @@
#ifndef NET_9P_CLIENT_H
#define NET_9P_CLIENT_H
#include <linux/utsname.h>
/* Number of requests per row */
#define P9_ROW_MAXTAG 255
@ -134,6 +136,7 @@ struct p9_req_t {
* @tagpool - transaction id accounting for session
* @reqs - 2D array of requests
* @max_tag - current maximum tag id allocated
* @name - node name used as client id
*
* The client structure is used to keep track of various per-client
* state that has been instantiated.
@ -164,6 +167,8 @@ struct p9_client {
struct p9_idpool *tagpool;
struct p9_req_t *reqs[P9_ROW_MAXTAG];
int max_tag;
char name[__NEW_UTS_LEN + 1];
};
/**

5
net/9p/client.c
View file

@ -992,6 +992,7 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
{
int err;
struct p9_client *clnt;
char *client_id;
err = 0;
clnt = kmalloc(sizeof(struct p9_client), GFP_KERNEL);
@ -1000,6 +1001,10 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
clnt->trans_mod = NULL;
clnt->trans = NULL;
client_id = utsname()->nodename;
memcpy(clnt->name, client_id, strlen(client_id) + 1);
spin_lock_init(&clnt->lock);
INIT_LIST_HEAD(&clnt->fidlist);