`hostname` needs to be set as null-pointer after free in
`cifs_put_tcp_session` function, or when `cifsd` thread attempts
to resolve hostname and reconnect the host, the thread would deref
the invalid pointer.
Here is one of practical backtrace examples as reference:
Task 477
---------------------------
do_mount
path_mount
do_new_mount
vfs_get_tree
smb3_get_tree
smb3_get_tree_common
cifs_smb3_do_mount
cifs_mount
mount_put_conns
cifs_put_tcp_session
--> kfree(server->hostname)
cifsd
---------------------------
kthread
cifs_demultiplex_thread
cifs_reconnect
reconn_set_ipaddr_from_hostname
--> if (!server->hostname)
--> if (server->hostname[0] == '\0') // !! UAF fault here
CIFS: VFS: cifs_mount failed w/return code = -112
mount error(112): Host is down
BUG: KASAN: use-after-free in reconn_set_ipaddr_from_hostname+0x2ba/0x310
Read of size 1 at addr ffff888108f35380 by task cifsd/480
CPU: 2 PID: 480 Comm: cifsd Not tainted 6.1.0-rc2-00106-gf705792f89dd-dirty #25
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x68/0x85
print_report+0x16c/0x4a3
kasan_report+0x95/0x190
reconn_set_ipaddr_from_hostname+0x2ba/0x310
__cifs_reconnect.part.0+0x241/0x800
cifs_reconnect+0x65f/0xb60
cifs_demultiplex_thread+0x1570/0x2570
kthread+0x2c5/0x380
ret_from_fork+0x22/0x30
</TASK>
Allocated by task 477:
kasan_save_stack+0x1e/0x40
kasan_set_track+0x21/0x30
__kasan_kmalloc+0x7e/0x90
__kmalloc_node_track_caller+0x52/0x1b0
kstrdup+0x3b/0x70
cifs_get_tcp_session+0xbc/0x19b0
mount_get_conns+0xa9/0x10c0
cifs_mount+0xdf/0x1970
cifs_smb3_do_mount+0x295/0x1660
smb3_get_tree+0x352/0x5e0
vfs_get_tree+0x8e/0x2e0
path_mount+0xf8c/0x1990
do_mount+0xee/0x110
__x64_sys_mount+0x14b/0x1f0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Freed by task 477:
kasan_save_stack+0x1e/0x40
kasan_set_track+0x21/0x30
kasan_save_free_info+0x2a/0x50
__kasan_slab_free+0x10a/0x190
__kmem_cache_free+0xca/0x3f0
cifs_put_tcp_session+0x30c/0x450
cifs_mount+0xf95/0x1970
cifs_smb3_do_mount+0x295/0x1660
smb3_get_tree+0x352/0x5e0
vfs_get_tree+0x8e/0x2e0
path_mount+0xf8c/0x1990
do_mount+0xee/0x110
__x64_sys_mount+0x14b/0x1f0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
The buggy address belongs to the object at ffff888108f35380
which belongs to the cache kmalloc-16 of size 16
The buggy address is located 0 bytes inside of
16-byte region [ffff888108f35380, ffff888108f35390)
The buggy address belongs to the physical page:
page:00000000333f8e58 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888108f350e0 pfn:0x108f35
flags: 0x200000000000200(slab|node=0|zone=2)
raw: 0200000000000200 0000000000000000 dead000000000122 ffff8881000423c0
raw: ffff888108f350e0 000000008080007a 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff888108f35280: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
ffff888108f35300: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
>ffff888108f35380: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
^
ffff888108f35400: fa fb fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888108f35480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Fixes: 7be3248f31 ("cifs: To match file servers, make sure the server hostname matches")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Steve French <stfrench@microsoft.com>
153695d36e