[v2] security/keys: fix slab-out-of-bounds in key_task_permission

Commit Message

Chen Ridong Oct. 8, 2024, 12:46 p.m. UTC

From: Chen Ridong <[e-mail]>

KASAN reports an out of bounds read:
BUG: KASAN: slab-out-of-bounds in __kuid_val include/linux/uidgid.h:36
BUG: KASAN: slab-out-of-bounds in uid_eq include/linux/uidgid.h:63 [inline]
BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410
security/keys/permission.c:54
Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362

CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-gafbffd6c3ede #15
Call Trace:
 __dump_stack lib/dump_stack.c:82 [inline]
 dump_stack+0x107/0x167 lib/dump_stack.c:123
 print_address_description.constprop.0+0x19/0x170 mm/kasan/report.c:400
 __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
 kasan_report+0x3a/0x50 mm/kasan/report.c:585
 __kuid_val include/linux/uidgid.h:36 [inline]
 uid_eq include/linux/uidgid.h:63 [inline]
 key_task_permission+0x394/0x410 security/keys/permission.c:54
 search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793

This issue was also reported by syzbot [1].

It can be reproduced by following these steps(more details [2]):
1. Obtain more than 32 inputs that have similar hashes, which ends with the
   pattern '0xxxxxxxe6'.
2. Reboot and add the keys obtained in step 1.

The reproducer demonstrates how this issue happened:
1. In the search_nested_keyrings function, when it iterates through the
   slots in a node(below tag ascend_to_node), if the slot pointer is meta
   and node->back_pointer != NULL(it means a root), it will proceed to
   descend_to_node. However, there is an exception. If node is the root,
   and one of the slots points to a shortcut, it will be treated as a
   keyring.
2. Whether the ptr is keyring decided by keyring_ptr_is_keyring function.
   However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as
   ASSOC_ARRAY_PTR_SUBTYPE_MASK.
3. When 32 keys with the similar hashes are added to the tree, the ROOT
   has keys with hashes that are not similar (e.g. slot 0) and it splits
   NODE A without using a shortcut. When NODE A is filled with keys that
   all hashes are xxe6, the keys are similar, NODE A will split with a
   shortcut. Finally, it forms the tree as shown below, where slot 6 points
   to a shortcut.

                      NODE A
              +------>+---+
      ROOT    |       | 0 | xxe6
      +---+   |       +---+
 xxxx | 0 | shortcut  :   : xxe6
      +---+   |       +---+
 xxe6 :   :   |       |   | xxe6
      +---+   |       +---+
      | 6 |---+       :   : xxe6
      +---+           +---+
 xxe6 :   :           | f | xxe6
      +---+           +---+
 xxe6 | f |
      +---+

4. As mentioned above, If a slot(slot 6) of the root points to a shortcut,
   it may be mistakenly transferred to a key*, leading to a read
   out-of-bounds read.

To fix this issue, one should jump to descend_to_node if the ptr is a
shortcut, regardless of whether the node is root or not.

[1] https://lore.kernel.org/all/[e-mail]/T/
[2] https://lore.kernel.org/linux-kernel/[e-mail]/

Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
Reported-by: [e-mail]
Signed-off-by: Chen Ridong <[e-mail]>
---
 security/keys/keyring.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Comments

Chen Ridong Oct. 16, 2024, 1:33 a.m. UTC | #1

On 2024/10/8 20:46, Chen Ridong wrote:
> From: Chen Ridong <[e-mail]>
> 
> KASAN reports an out of bounds read:
> BUG: KASAN: slab-out-of-bounds in __kuid_val include/linux/uidgid.h:36
> BUG: KASAN: slab-out-of-bounds in uid_eq include/linux/uidgid.h:63 [inline]
> BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410
> security/keys/permission.c:54
> Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362
> 
> CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-gafbffd6c3ede #15
> Call Trace:
>   __dump_stack lib/dump_stack.c:82 [inline]
>   dump_stack+0x107/0x167 lib/dump_stack.c:123
>   print_address_description.constprop.0+0x19/0x170 mm/kasan/report.c:400
>   __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
>   kasan_report+0x3a/0x50 mm/kasan/report.c:585
>   __kuid_val include/linux/uidgid.h:36 [inline]
>   uid_eq include/linux/uidgid.h:63 [inline]
>   key_task_permission+0x394/0x410 security/keys/permission.c:54
>   search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793
> 
> This issue was also reported by syzbot [1].
> 
> It can be reproduced by following these steps(more details [2]):
> 1. Obtain more than 32 inputs that have similar hashes, which ends with the
>     pattern '0xxxxxxxe6'.
> 2. Reboot and add the keys obtained in step 1.
> 
> The reproducer demonstrates how this issue happened:
> 1. In the search_nested_keyrings function, when it iterates through the
>     slots in a node(below tag ascend_to_node), if the slot pointer is meta
>     and node->back_pointer != NULL(it means a root), it will proceed to
>     descend_to_node. However, there is an exception. If node is the root,
>     and one of the slots points to a shortcut, it will be treated as a
>     keyring.
> 2. Whether the ptr is keyring decided by keyring_ptr_is_keyring function.
>     However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as
>     ASSOC_ARRAY_PTR_SUBTYPE_MASK.
> 3. When 32 keys with the similar hashes are added to the tree, the ROOT
>     has keys with hashes that are not similar (e.g. slot 0) and it splits
>     NODE A without using a shortcut. When NODE A is filled with keys that
>     all hashes are xxe6, the keys are similar, NODE A will split with a
>     shortcut. Finally, it forms the tree as shown below, where slot 6 points
>     to a shortcut.
> 
>                        NODE A
>                +------>+---+
>        ROOT    |       | 0 | xxe6
>        +---+   |       +---+
>   xxxx | 0 | shortcut  :   : xxe6
>        +---+   |       +---+
>   xxe6 :   :   |       |   | xxe6
>        +---+   |       +---+
>        | 6 |---+       :   : xxe6
>        +---+           +---+
>   xxe6 :   :           | f | xxe6
>        +---+           +---+
>   xxe6 | f |
>        +---+
> 
> 4. As mentioned above, If a slot(slot 6) of the root points to a shortcut,
>     it may be mistakenly transferred to a key*, leading to a read
>     out-of-bounds read.
> 
> To fix this issue, one should jump to descend_to_node if the ptr is a
> shortcut, regardless of whether the node is root or not.
> 
> [1] https://lore.kernel.org/all/[e-mail]/T/
> [2] https://lore.kernel.org/linux-kernel/[e-mail]/
> 
> Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
> Reported-by: [e-mail]
> Signed-off-by: Chen Ridong <[e-mail]>
> ---
>   security/keys/keyring.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> index 4448758f643a..f331725d5a37 100644
> --- a/security/keys/keyring.c
> +++ b/security/keys/keyring.c
> @@ -772,8 +772,11 @@ static bool search_nested_keyrings(struct key *keyring,
>   	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
>   		ptr = READ_ONCE(node->slots[slot]);
>   
> -		if (assoc_array_ptr_is_meta(ptr) && node->back_pointer)
> -			goto descend_to_node;
> +		if (assoc_array_ptr_is_meta(ptr)) {
> +			if (node->back_pointer ||
> +			    assoc_array_ptr_is_shortcut(ptr))
> +				goto descend_to_node;
> +		}
>   
>   		if (!keyring_ptr_is_keyring(ptr))
>   			continue;

Friendly ping.

Best regards,
Ridong

Jarkko Sakkinen Oct. 16, 2024, 5:08 a.m. UTC | #2

On Wed, 2024-10-16 at 09:33 +0800, Chen Ridong wrote:
> 
> 
> On 2024/10/8 20:46, Chen Ridong wrote:
> > From: Chen Ridong <[e-mail]>
> > 
> > KASAN reports an out of bounds read:
> > BUG: KASAN: slab-out-of-bounds in __kuid_val
> > include/linux/uidgid.h:36
> > BUG: KASAN: slab-out-of-bounds in uid_eq include/linux/uidgid.h:63
> > [inline]
> > BUG: KASAN: slab-out-of-bounds in key_task_permission+0x394/0x410
> > security/keys/permission.c:54
> > Read of size 4 at addr ffff88813c3ab618 by task stress-ng/4362
> > 
> > CPU: 2 PID: 4362 Comm: stress-ng Not tainted 5.10.0-14930-
> > gafbffd6c3ede #15
> > Call Trace:
> >   __dump_stack lib/dump_stack.c:82 [inline]
> >   dump_stack+0x107/0x167 lib/dump_stack.c:123
> >   print_address_description.constprop.0+0x19/0x170
> > mm/kasan/report.c:400
> >   __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
> >   kasan_report+0x3a/0x50 mm/kasan/report.c:585
> >   __kuid_val include/linux/uidgid.h:36 [inline]
> >   uid_eq include/linux/uidgid.h:63 [inline]
> >   key_task_permission+0x394/0x410 security/keys/permission.c:54
> >   search_nested_keyrings+0x90e/0xe90 security/keys/keyring.c:793
> > 
> > This issue was also reported by syzbot [1].
> > 
> > It can be reproduced by following these steps(more details [2]):
> > 1. Obtain more than 32 inputs that have similar hashes, which ends
> > with the
> >     pattern '0xxxxxxxe6'.
> > 2. Reboot and add the keys obtained in step 1.
> > 
> > The reproducer demonstrates how this issue happened:
> > 1. In the search_nested_keyrings function, when it iterates through
> > the
> >     slots in a node(below tag ascend_to_node), if the slot pointer
> > is meta
> >     and node->back_pointer != NULL(it means a root), it will
> > proceed to
> >     descend_to_node. However, there is an exception. If node is the
> > root,
> >     and one of the slots points to a shortcut, it will be treated
> > as a
> >     keyring.
> > 2. Whether the ptr is keyring decided by keyring_ptr_is_keyring
> > function.
> >     However, KEYRING_PTR_SUBTYPE is 0x2UL, the same as
> >     ASSOC_ARRAY_PTR_SUBTYPE_MASK.
> > 3. When 32 keys with the similar hashes are added to the tree, the
> > ROOT
> >     has keys with hashes that are not similar (e.g. slot 0) and it
> > splits
> >     NODE A without using a shortcut. When NODE A is filled with
> > keys that
> >     all hashes are xxe6, the keys are similar, NODE A will split
> > with a
> >     shortcut. Finally, it forms the tree as shown below, where slot
> > 6 points
> >     to a shortcut.
> > 
> >                        NODE A
> >                +------>+---+
> >        ROOT    |       | 0 | xxe6
> >        +---+   |       +---+
> >   xxxx | 0 | shortcut  :   : xxe6
> >        +---+   |       +---+
> >   xxe6 :   :   |       |   | xxe6
> >        +---+   |       +---+
> >        | 6 |---+       :   : xxe6
> >        +---+           +---+
> >   xxe6 :   :           | f | xxe6
> >        +---+           +---+
> >   xxe6 | f |
> >        +---+
> > 
> > 4. As mentioned above, If a slot(slot 6) of the root points to a
> > shortcut,
> >     it may be mistakenly transferred to a key*, leading to a read
> >     out-of-bounds read.
> > 
> > To fix this issue, one should jump to descend_to_node if the ptr is
> > a
> > shortcut, regardless of whether the node is root or not.
> > 
> > [1]
> > https://lore.kernel.org/all/[e-mail]/T/
> > [2]
> > https://lore.kernel.org/linux-kernel/[e-mail]/
> > 
> > Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
> > Reported-by: [e-mail]
> > Signed-off-by: Chen Ridong <[e-mail]>
> > ---
> >   security/keys/keyring.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> > index 4448758f643a..f331725d5a37 100644
> > --- a/security/keys/keyring.c
> > +++ b/security/keys/keyring.c
> > @@ -772,8 +772,11 @@ static bool search_nested_keyrings(struct key
> > *keyring,
> >   	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
> >   		ptr = READ_ONCE(node->slots[slot]);
> >   
> > -		if (assoc_array_ptr_is_meta(ptr) && node-
> > >back_pointer)
> > -			goto descend_to_node;
> > +		if (assoc_array_ptr_is_meta(ptr)) {
> > +			if (node->back_pointer ||
> > +			    assoc_array_ptr_is_shortcut(ptr))
> > +				goto descend_to_node;
> > +		}
> >   
> >   		if (!keyring_ptr_is_keyring(ptr))
> >   			continue;
> 
> Friendly ping.

Thanks for pinging because I actually accidentally missed the original
email!

Reviewed-by: Jarkko Sakkinen <[e-mail]>

I'll pick this up.

> 
> Best regards,
> Ridong
> 
> 

BR, Jarkko

Jarkko Sakkinen Oct. 16, 2024, 5:14 a.m. UTC | #3

On Wed, 2024-10-16 at 08:08 +0300, Jarkko Sakkinen wrote:
> > Friendly ping.
> 
> Thanks for pinging because I actually accidentally missed the
> original
> email!
> 
> Reviewed-by: Jarkko Sakkinen <[e-mail]>
> 
> I'll pick this up.

I tuned the commit message just a bit (see my comment
embedded):

https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?id=9bb3ba75c1c8fd8c9f6a0b1fd6409b725583a3e0

BR, Jarkko

Chen Ridong Oct. 17, 2024, 1:19 a.m. UTC | #4

On 2024/10/16 13:14, Jarkko Sakkinen wrote:
> On Wed, 2024-10-16 at 08:08 +0300, Jarkko Sakkinen wrote:
>>> Friendly ping.
>>
>> Thanks for pinging because I actually accidentally missed the
>> original
>> email!
>>
>> Reviewed-by: Jarkko Sakkinen <[e-mail]>
>>
>> I'll pick this up.
> 
> I tuned the commit message just a bit (see my comment
> embedded):
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?id=9bb3ba75c1c8fd8c9f6a0b1fd6409b725583a3e0
> 
> BR, Jarkko

Thanks you very much.

Best regards,
Ridong

Jarkko Sakkinen Oct. 17, 2024, 8:39 a.m. UTC | #5

On Thu, 2024-10-17 at 09:19 +0800, Chen Ridong wrote:
> 
> 
> On 2024/10/16 13:14, Jarkko Sakkinen wrote:
> > On Wed, 2024-10-16 at 08:08 +0300, Jarkko Sakkinen wrote:
> > > > Friendly ping.
> > > 
> > > Thanks for pinging because I actually accidentally missed the
> > > original
> > > email!
> > > 
> > > Reviewed-by: Jarkko Sakkinen <[e-mail]>
> > > 
> > > I'll pick this up.
> > 
> > I tuned the commit message just a bit (see my comment
> > embedded):
> > 
> > https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?id=9bb3ba75c1c8fd8c9f6a0b1fd6409b725583a3e0
> > 
> > BR, Jarkko
> 
> Thanks you very much.

Thanks to you for patience with my earlier shitty reviews ;-) That was 
tbh the main issue with this bug fix getting through...

> Best regards,
> Ridong

BR, Jarkko

Patch

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 4448758f643a..f331725d5a37 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -772,8 +772,11 @@  static bool search_nested_keyrings(struct key *keyring,
 	for (; slot < ASSOC_ARRAY_FAN_OUT; slot++) {
 		ptr = READ_ONCE(node->slots[slot]);
 
-		if (assoc_array_ptr_is_meta(ptr) && node->back_pointer)
-			goto descend_to_node;
+		if (assoc_array_ptr_is_meta(ptr)) {
+			if (node->back_pointer ||
+			    assoc_array_ptr_is_shortcut(ptr))
+				goto descend_to_node;
+		}
 
 		if (!keyring_ptr_is_keyring(ptr))
 			continue;