131 lines
5.7 KiB
Diff
131 lines
5.7 KiB
Diff
From 7289bfaee2a42bdb56eecab0625907c045d080ba Mon Sep 17 00:00:00 2001
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From: Eric Biggers <ebiggers@google.com>
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Date: Wed, 27 Sep 2017 12:50:41 -0700
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Subject: [PATCH] KEYS: don't let add_key() update an uninstantiated key
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Currently, add_key() will, when passed a key that already exists, call
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the key's ->update() method. But this is heavily broken in the case
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where the key is uninstantiated because it doesn't call
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__key_instantiate_and_link(). Consequently, it doesn't do most of the
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things that are supposed to happen when the key is instantiated, such as
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setting KEY_FLAG_INSTANTIATED, clearing KEY_FLAG_USER_CONSTRUCT and
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awakening tasks waiting on it, and incrementing key->user->nikeys.
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It also never takes key_construction_mutex, which means that
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->instantiate() can run concurrently with ->update() on the same key.
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In the case of the "user" and "logon" key types this causes a memory
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leak, at best. Maybe even worse, the ->update() methods of the
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"encrypted" and "trusted" key types actually just dereference a NULL
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pointer when passed an uninstantiated key.
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Therefore, change find_key_to_update() to return NULL if the found key
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is uninstantiated, so that add_key() replaces the key rather than
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instantiating it. This seems to be better than fixing __key_update() to
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call __key_instantiate_and_link(), since given all the bugs noted above
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as well as that the existing behavior was undocumented and
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keyctl_instantiate() is supposed to be used instead, I doubt anyone was
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relying on the existing behavior.
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This patch only affects *uninstantiated* keys. For now we still allow a
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negatively instantiated key to be updated (thereby positively
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instantiating it), although that's broken too (the next patch fixes it)
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and I'm not sure that anyone actually uses that functionality either.
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Here is a simple reproducer for the bug using the "encrypted" key type
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(requires CONFIG_ENCRYPTED_KEYS=y), though as noted above the bug
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pertained to more than just the "encrypted" key type:
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#include <stdlib.h>
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#include <unistd.h>
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#include <keyutils.h>
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int main(void)
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{
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int ringid = keyctl_join_session_keyring(NULL);
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if (fork()) {
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for (;;) {
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const char payload[] = "update user:foo 32";
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usleep(rand() % 10000);
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add_key("encrypted", "desc", payload, sizeof(payload), ringid);
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keyctl_clear(ringid);
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}
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} else {
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for (;;)
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request_key("encrypted", "desc", "callout_info", ringid);
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}
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}
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It causes:
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BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
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IP: encrypted_update+0xb0/0x170
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PGD 7a178067 P4D 7a178067 PUD 77269067 PMD 0
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PREEMPT SMP
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CPU: 0 PID: 340 Comm: reproduce Tainted: G D 4.14.0-rc1-00025-g428490e38b2e #796
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Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
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task: ffff8a467a39a340 task.stack: ffffb15c40770000
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RIP: 0010:encrypted_update+0xb0/0x170
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RSP: 0018:ffffb15c40773de8 EFLAGS: 00010246
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RAX: 0000000000000000 RBX: ffff8a467a275b00 RCX: 0000000000000000
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RDX: 0000000000000005 RSI: ffff8a467a275b14 RDI: ffffffffb742f303
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RBP: ffffb15c40773e20 R08: 0000000000000000 R09: ffff8a467a275b17
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R10: 0000000000000020 R11: 0000000000000000 R12: 0000000000000000
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R13: 0000000000000000 R14: ffff8a4677057180 R15: ffff8a467a275b0f
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FS: 00007f5d7fb08700(0000) GS:ffff8a467f200000(0000) knlGS:0000000000000000
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CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
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CR2: 0000000000000018 CR3: 0000000077262005 CR4: 00000000001606f0
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Call Trace:
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key_create_or_update+0x2bc/0x460
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SyS_add_key+0x10c/0x1d0
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entry_SYSCALL_64_fastpath+0x1f/0xbe
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RIP: 0033:0x7f5d7f211259
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RSP: 002b:00007ffed03904c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000f8
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RAX: ffffffffffffffda RBX: 000000003b2a7955 RCX: 00007f5d7f211259
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RDX: 00000000004009e4 RSI: 00000000004009ff RDI: 0000000000400a04
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RBP: 0000000068db8bad R08: 000000003b2a7955 R09: 0000000000000004
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R10: 000000000000001a R11: 0000000000000246 R12: 0000000000400868
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R13: 00007ffed03905d0 R14: 0000000000000000 R15: 0000000000000000
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Code: 77 28 e8 64 34 1f 00 45 31 c0 31 c9 48 8d 55 c8 48 89 df 48 8d 75 d0 e8 ff f9 ff ff 85 c0 41 89 c4 0f 88 84 00 00 00 4c 8b 7d c8 <49> 8b 75 18 4c 89 ff e8 24 f8 ff ff 85 c0 41 89 c4 78 6d 49 8b
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RIP: encrypted_update+0xb0/0x170 RSP: ffffb15c40773de8
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CR2: 0000000000000018
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Cc: <stable@vger.kernel.org> [v2.6.12+]
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Signed-off-by: Eric Biggers <ebiggers@google.com>
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---
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security/keys/keyring.c | 10 ++++++----
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1 file changed, 6 insertions(+), 4 deletions(-)
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diff --git a/security/keys/keyring.c b/security/keys/keyring.c
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index 4fa82a8a9c0e..129a4175760b 100644
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--- a/security/keys/keyring.c
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+++ b/security/keys/keyring.c
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@@ -1056,8 +1056,8 @@ EXPORT_SYMBOL(keyring_restrict);
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* caller must also hold a lock on the keyring semaphore.
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*
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* Returns a pointer to the found key with usage count incremented if
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- * successful and returns NULL if not found. Revoked and invalidated keys are
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- * skipped over.
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+ * successful and returns NULL if not found. Revoked, invalidated, and
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+ * uninstantiated keys are skipped over. (But negative keys are not!)
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*
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* If successful, the possession indicator is propagated from the keyring ref
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* to the returned key reference.
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@@ -1084,8 +1084,10 @@ key_ref_t find_key_to_update(key_ref_t keyring_ref,
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found:
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key = keyring_ptr_to_key(object);
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- if (key->flags & ((1 << KEY_FLAG_INVALIDATED) |
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- (1 << KEY_FLAG_REVOKED))) {
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+ if ((key->flags & ((1 << KEY_FLAG_INVALIDATED) |
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+ (1 << KEY_FLAG_REVOKED) |
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+ (1 << KEY_FLAG_INSTANTIATED))) !=
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+ (1 << KEY_FLAG_INSTANTIATED)) {
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kleave(" = NULL [x]");
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return NULL;
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}
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--
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2.13.6
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