• David Howells's avatar
    DNS: Fix a NULL pointer deref when trying to read an error key [CVE-2011-1076] · 1362fa07
    David Howells authored
    When a DNS resolver key is instantiated with an error indication, attempts to
    read that key will result in an oops because user_read() is expecting there to
    be a payload - and there isn't one [CVE-2011-1076].
    
    Give the DNS resolver key its own read handler that returns the error cached in
    key->type_data.x[0] as an error rather than crashing.
    
    Also make the kenter() at the beginning of dns_resolver_instantiate() limit the
    amount of data it prints, since the data is not necessarily NUL-terminated.
    
    The buggy code was added in:
    
    	commit 4a2d7892
    	Author: Wang Lei <wang840925@gmail.com>
    	Date:   Wed Aug 11 09:37:58 2010 +0100
    	Subject: DNS: If the DNS server returns an error, allow that to be cached [ver #2]
    
    This can trivially be reproduced by any user with the following program
    compiled with -lkeyutils:
    
    	#include <stdlib.h>
    	#include <keyutils.h>
    	#include <err.h>
    	static char payload[] = "#dnserror=6";
    	int main()
    	{
    		key_serial_t key;
    		key = add_key("dns_resolver", "a", payload, sizeof(payload),
    			      KEY_SPEC_SESSION_KEYRING);
    		if (key == -1)
    			err(1, "add_key");
    		if (keyctl_read(key, NULL, 0) == -1)
    			err(1, "read_key");
    		return 0;
    	}
    
    What should happen is that keyctl_read() reports error 6 (ENXIO) to the user:
    
    	dns-break: read_key: No such device or address
    
    but instead the kernel oopses.
    
    This cannot be reproduced with the 'keyutils add' or 'keyutils padd' commands
    as both of those cut the data down below the NUL termination that must be
    included in the data.  Without this dns_resolver_instantiate() will return
    -EINVAL and the key will not be instantiated such that it can be read.
    
    The oops looks like:
    
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
    IP: [<ffffffff811b99f7>] user_read+0x4f/0x8f
    PGD 3bdf8067 PUD 385b9067 PMD 0
    Oops: 0000 [#1] SMP
    last sysfs file: /sys/devices/pci0000:00/0000:00:19.0/irq
    CPU 0
    Modules linked in:
    
    Pid: 2150, comm: dns-break Not tainted 2.6.38-rc7-cachefs+ #468                  /DG965RY
    RIP: 0010:[<ffffffff811b99f7>]  [<ffffffff811b99f7>] user_read+0x4f/0x8f
    RSP: 0018:ffff88003bf47f08  EFLAGS: 00010246
    RAX: 0000000000000001 RBX: ffff88003b5ea378 RCX: ffffffff81972368
    RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88003b5ea378
    RBP: ffff88003bf47f28 R08: ffff88003be56620 R09: 0000000000000000
    R10: 0000000000000395 R11: 0000000000000002 R12: 0000000000000000
    R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffffffffa1
    FS:  00007feab5751700(0000) GS:ffff88003e000000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000010 CR3: 000000003de40000 CR4: 00000000000006f0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
    Process dns-break (pid: 2150, threadinfo ffff88003bf46000, task ffff88003be56090)
    Stack:
     ffff88003b5ea378 ffff88003b5ea3a0 0000000000000000 0000000000000000
     ffff88003bf47f68 ffffffff811b708e ffff88003c442bc8 0000000000000000
     00000000004005a0 00007fffba368060 0000000000000000 0000000000000000
    Call Trace:
     [<ffffffff811b708e>] keyctl_read_key+0xac/0xcf
     [<ffffffff811b7c07>] sys_keyctl+0x75/0xb6
     [<ffffffff81001f7b>] system_call_fastpath+0x16/0x1b
    Code: 75 1f 48 83 7b 28 00 75 18 c6 05 58 2b fb 00 01 be bb 00 00 00 48 c7 c7 76 1c 75 81 e8 13 c2 e9 ff 4c 8b b3 e0 00 00 00 4d 85 ed <41> 0f b7 5e 10 74 2d 4d 85 e4 74 28 e8 98 79 ee ff 49 39 dd 48
    RIP  [<ffffffff811b99f7>] user_read+0x4f/0x8f
     RSP <ffff88003bf47f08>
    CR2: 0000000000000010
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Acked-by: default avatarJeff Layton <jlayton@redhat.com>
    cc: Wang Lei <wang840925@gmail.com>
    Signed-off-by: default avatarJames Morris <jmorris@namei.org>
    1362fa07
dns_key.c 7.88 KB