From: Chen Ridong chenridong@huawei.com

Offering: HULK hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IAU173

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The following bug was triggered when performing syzkaller test: 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 keyring_search_rcu+0x1b6/0x310 security/keys/keyring.c:922 search_cred_keyrings_rcu+0x111/0x2e0 security/keys/process_keys.c:459 search_process_keyrings_rcu+0x1d/0x310 security/keys/process_keys.c:544 lookup_user_key+0x782/0x12e0 security/keys/process_keys.c:762 keyctl_invalidate_key+0x20/0x190 security/keys/keyctl.c:434 __do_sys_keyctl security/keys/keyctl.c:1978 [inline] __se_sys_keyctl+0x1de/0x5b0 security/keys/keyctl.c:1880 do_syscall_64+0x30/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1

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 end 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), and the slot pointer is meta and node->back_pointer != NULL, 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 be transferred to a key*, leading to an read out-of-bounds read.

To fix this issue, one should jump to descend_to_node if the pointer is a shortcut.

[1] https://lore.kernel.org/all/000000000000cbb7860611f61147@google.com/T/ [2] https://lore.kernel.org/linux-kernel/1cfa878e-8c7b-4570-8606-21daf5e13ce7@hu...

Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring") Reported-by: syzbot+5b415c07907a2990d1a3@syzkaller.appspotmail.com Signed-off-by: Chen Ridong chenridong@huawei.com Signed-off-by: Yi Yang yiyang13@huawei.com --- security/keys/keyring.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c index e8f2366021ea..8a6d891be55e 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -739,7 +739,9 @@ 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) + if (assoc_array_ptr_is_meta(ptr) && + (node->back_pointer || + assoc_array_ptr_is_shortcut(ptr))) goto descend_to_node;

if (!keyring_ptr_is_keyring(ptr))