kernel BUG at security/keys/keyring.c:LINE!

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: befad944e231 Merge tag 'drm-fixes-2018-10-05' of git://ano..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=161fc976400000
kernel config: https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
dashboard link: https://syzkaller.appspot.com/bug?extid=ec24e95ea483de0a24da
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10160e3a400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16995491400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ec24e9...@syzkaller.appspotmail.com

------------[ cut here ]------------
kernel BUG at security/keys/keyring.c:1214!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5807 Comm: syz-executor226 Not tainted 4.19.0-rc6+ #268
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:__key_link_begin+0x23a/0x300 security/keys/keyring.c:1214
Code: fe 48 c7 c7 20 ae 67 89 e8 b3 36 23 fe eb ac e8 ec 64 42 fe 48 c7 c7
20 ae 67 89 e8 30 73 73 04 e9 e3 fe ff ff e8 d6 64 42 fe <0f> 0b e8 cf 64
42 fe 48 8d bb ce 00 00 00 48 b8 00 00 00 00 00 fc
RSP: 0018:ffff8801bbdc7b10 EFLAGS: 00010293
RAX: ffff8801d924e2c0 RBX: ffff8801d4e7e080 RCX: ffffffff833c4ebf
RDX: 0000000000000000 RSI: ffffffff833c50aa RDI: 0000000000000007
RBP: ffff8801bbdc7b40 R08: ffff8801d924e2c0 R09: fffffbfff12cf4a4
R10: fffffbfff12cf4a4 R11: ffffffff8967a523 R12: ffff8801bbdc7c48
R13: 0000000000000000 R14: ffff8801d4e7e200 R15: ffff8801d4e7e080
FS: 0000000001ce9880(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020cab000 CR3: 00000001d829a000 CR4: 00000000001406f0
Call Trace:
construct_alloc_key security/keys/request_key.c:389 [inline]
construct_key_and_link security/keys/request_key.c:480 [inline]
request_key_and_link+0x737/0x17a0 security/keys/request_key.c:593
__do_sys_request_key security/keys/keyctl.c:213 [inline]
__se_sys_request_key security/keys/keyctl.c:158 [inline]
__x64_sys_request_key+0x305/0x400 security/keys/keyctl.c:158
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440169
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd70324808 EFLAGS: 00000217 ORIG_RAX: 00000000000000f9
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440169
RDX: 00000000200001c0 RSI: 0000000020000180 RDI: 00000000200000c0
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000111522d3 R11: 0000000000000217 R12: 00000000004019f0
R13: 0000000000401a80 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 40815c4a8f1e2472 ]---
RIP: 0010:__key_link_begin+0x23a/0x300 security/keys/keyring.c:1214
Code: fe 48 c7 c7 20 ae 67 89 e8 b3 36 23 fe eb ac e8 ec 64 42 fe 48 c7 c7
20 ae 67 89 e8 30 73 73 04 e9 e3 fe ff ff e8 d6 64 42 fe <0f> 0b e8 cf 64
42 fe 48 8d bb ce 00 00 00 48 b8 00 00 00 00 00 fc
RSP: 0018:ffff8801bbdc7b10 EFLAGS: 00010293
RAX: ffff8801d924e2c0 RBX: ffff8801d4e7e080 RCX: ffffffff833c4ebf
RDX: 0000000000000000 RSI: ffffffff833c50aa RDI: 0000000000000007
RBP: ffff8801bbdc7b40 R08: ffff8801d924e2c0 R09: fffffbfff12cf4a4
R10: fffffbfff12cf4a4 R11: ffffffff8967a523 R12: ffff8801bbdc7c48
R13: 0000000000000000 R14: ffff8801d4e7e200 R15: ffff8801d4e7e080
FS: 0000000001ce9880(0000) GS:ffff8801dae00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020cab000 CR3: 00000001d829a000 CR4: 00000000001406f0


---
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[Eric Biggers]

From: Eric Biggers <ebig...@google.com>

syzbot hit the 'BUG_ON(index_key->desc_len == 0);' in __key_link_begin()
called from construct_alloc_key() during sys_request_key(), because the
length of the key description was never calculated.

The problem is that we rely on ->desc_len being initialized by
search_process_keyrings(), specifically by search_nested_keyrings().
But, if the process isn't subscribed to any keyrings that never happens.

Fix it by always initializing keyring_index_key::desc_len as soon as the
description is set, like we already do in some places.

The following program reproduces the BUG_ON() when it's run as root and
no session keyring has been installed. If it doesn't work, try removing
pam_keyinit.so from /etc/pam.d/login and rebooting.

#include <stdlib.h>
#include <unistd.h>
#include <keyutils.h>

int main(void)
{
int id = add_key("keyring", "syz", NULL, 0, KEY_SPEC_USER_KEYRING);

keyctl_setperm(id, KEY_OTH_WRITE);
setreuid(5000, 5000);
request_key("user", "desc", "", id);
}

Reported-by: syzbot+ec24e9...@syzkaller.appspotmail.com
Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
Cc: <sta...@vger.kernel.org> # v3.13+
Signed-off-by: Eric Biggers <ebig...@google.com>
---
security/keys/keyring.c | 4 +---
security/keys/proc.c | 1 +
security/keys/request_key.c | 1 +
security/keys/request_key_auth.c | 2 +-
4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 41bcf57e96f2..99a55145ddcd 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -661,9 +661,6 @@ static bool search_nested_keyrings(struct key *keyring,
BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
(ctx->flags & STATE_CHECKS) == STATE_CHECKS);

- if (ctx->index_key.description)
- ctx->index_key.desc_len = strlen(ctx->index_key.description);
-
/* Check to see if this top-level keyring is what we are looking for
* and whether it is valid or not.
*/
@@ -914,6 +911,7 @@ key_ref_t keyring_search(key_ref_t keyring,
struct keyring_search_context ctx = {
.index_key.type = type,
.index_key.description = description,
+ .index_key.desc_len = strlen(description),
.cred = current_cred(),
.match_data.cmp = key_default_cmp,
.match_data.raw_data = description,
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 5af2934965d8..909f6c5270a1 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -168,6 +168,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
struct keyring_search_context ctx = {
.index_key.type = key->type,
.index_key.description = key->description,
+ .index_key.desc_len = strlen(key->description),
.cred = m->file->f_cred,
.match_data.cmp = lookup_user_key_possessed,
.match_data.raw_data = key,
diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 114f7408feee..738553698649 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -545,6 +545,7 @@ struct key *request_key_and_link(struct key_type *type,
struct keyring_search_context ctx = {
.index_key.type = type,
.index_key.description = description,
+ .index_key.desc_len = strlen(description),
.cred = current_cred(),
.match_data.cmp = key_default_cmp,
.match_data.raw_data = description,
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 424e1d90412e..6797843154f0 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -246,7 +246,7 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id)
struct key *authkey;
key_ref_t authkey_ref;

- sprintf(description, "%x", target_id);
+ ctx.index_key.desc_len = sprintf(description, "%x", target_id);

authkey_ref = search_process_keyrings(&ctx);

--
2.19.1.930.g4563a0d9d0-goog

[Eric Biggers]

It's actually possible to just set '.index_key = key->index_key' here.
I'll send v2 with that instead.

- Eric

[Eric Biggers]

v2: In proc_keys_show(), assign index_key directly

security/keys/keyring.c | 4 +---
security/keys/proc.c | 3 +--

security/keys/request_key.c | 1 +
security/keys/request_key_auth.c | 2 +-

4 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 41bcf57e96f21..99a55145ddcd2 100644

--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -661,9 +661,6 @@ static bool search_nested_keyrings(struct key *keyring,
BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||
(ctx->flags & STATE_CHECKS) == STATE_CHECKS);

- if (ctx->index_key.description)
- ctx->index_key.desc_len = strlen(ctx->index_key.description);
-
/* Check to see if this top-level keyring is what we are looking for
* and whether it is valid or not.
*/
@@ -914,6 +911,7 @@ key_ref_t keyring_search(key_ref_t keyring,
struct keyring_search_context ctx = {
.index_key.type = type,
.index_key.description = description,
+ .index_key.desc_len = strlen(description),
.cred = current_cred(),
.match_data.cmp = key_default_cmp,
.match_data.raw_data = description,
diff --git a/security/keys/proc.c b/security/keys/proc.c

index 5af2934965d80..d38be9db2cc07 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -166,8 +166,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
int rc;

struct keyring_search_context ctx = {
- .index_key.type = key->type,
- .index_key.description = key->description,
+ .index_key = key->index_key,

.cred = m->file->f_cred,
.match_data.cmp = lookup_user_key_possessed,
.match_data.raw_data = key,

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 114f7408feee6..7385536986497 100644

--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -545,6 +545,7 @@ struct key *request_key_and_link(struct key_type *type,

struct keyring_search_context ctx = {
.index_key.type = type,
.index_key.description = description,
+ .index_key.desc_len = strlen(description),
.cred = current_cred(),
.match_data.cmp = key_default_cmp,
.match_data.raw_data = description,

diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 424e1d90412ea..6797843154f03 100644

[Eric Biggers]

Ping. David, are you planning to apply this?

- Eric

[Eric Biggers]

Ping.

[Eric Biggers]

On Wed, Nov 28, 2018 at 03:19:41PM -0800, Eric Biggers wrote:

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Ping.

[Eric Biggers]

[Eric Biggers]

Hi James, can you please apply this for v5.1? This has been ignored by David
for over 3 months with repeated pings.

- Eric