linux-kernel - [PATCH 1/2] kprobes: Fix __get_insn_slot() after __counted

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20241030-kprobes-fix-counted-by-annotation-v1-1-8f266001fad0@kernel.org>
Date: Wed, 30 Oct 2024 09:14:48 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Masami Hiramatsu <mhiramat@...nel.org>, 
 Naveen N Rao <naveen@...nel.org>, 
 Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>, 
 "David S. Miller" <davem@...emloft.net>
Cc: Kees Cook <kees@...nel.org>, 
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
 Jinjie Ruan <ruanjinjie@...wei.com>, linux-kernel@...r.kernel.org, 
 linux-trace-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, 
 patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH 1/2] kprobes: Fix __get_insn_slot() after __counted_by
 annotation

Commit 0888460c9050 ("kprobes: Annotate structs with __counted_by()")
added a __counted_by annotation without adjusting the code for the
__counted_by requirements, resulting in a panic when UBSAN_BOUNDS and
FORTIFY_SOURCE are enabled:

  | memset: detected buffer overflow: 512 byte write of buffer size 0
  | WARNING: CPU: 0 PID: 1 at lib/string_helpers.c:1032 __fortify_report+0x64/0x80
  | Call Trace:
  |  __fortify_report+0x60/0x80 (unreliable)
  |  __fortify_panic+0x18/0x1c
  |  __get_insn_slot+0x33c/0x340

__counted_by requires that the counter be set before accessing the
flexible array but ->nused is not set until after ->slot_used is
accessed via memset(). Even if the current ->nused assignment were moved
up before memset(), the value of 1 would be incorrect because the entire
array is being accessed, not just one element.

Set ->nused to the full number of slots from slots_per_page() before
calling memset() to resolve the panic. While it is not strictly
necessary because of the new assignment, move the existing ->nused
assignment above accessing ->slot_used[0] for visual consistency.

The value of slots_per_page() should not change throughout
__get_insn_slot() because ->insn_size is never modified after its
initial assignment (which has to be done by this point otherwise it
would be incorrect) and the other values are constants, so use a new
variable to reuse its value directly.

Fixes: 0888460c9050 ("kprobes: Annotate structs with __counted_by()")
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 kernel/kprobes.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 98d71a5acb723ddfff3efcc44cc6754ee36ec1de..2cf4628bc97ce2ae18547b513cd75b6350e9cc9c 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -145,16 +145,18 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 {
 	struct kprobe_insn_page *kip;
 	kprobe_opcode_t *slot = NULL;
+	int num_slots;

 	/* Since the slot array is not protected by rcu, we need a mutex */
 	mutex_lock(&c->mutex);
+	num_slots = slots_per_page(c);
  retry:
 	rcu_read_lock();
 	list_for_each_entry_rcu(kip, &c->pages, list) {
-		if (kip->nused < slots_per_page(c)) {
+		if (kip->nused < num_slots) {
 			int i;

-			for (i = 0; i < slots_per_page(c); i++) {
+			for (i = 0; i < num_slots; i++) {
 				if (kip->slot_used[i] == SLOT_CLEAN) {
 					kip->slot_used[i] = SLOT_USED;
 					kip->nused++;
@@ -164,7 +166,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 				}
 			}
 			/* kip->nused is broken. Fix it. */
-			kip->nused = slots_per_page(c);
+			kip->nused = num_slots;
 			WARN_ON(1);
 		}
 	}
@@ -175,7 +177,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 		goto retry;

 	/* All out of space.  Need to allocate a new page. */
-	kip = kmalloc(KPROBE_INSN_PAGE_SIZE(slots_per_page(c)), GFP_KERNEL);
+	kip = kmalloc(KPROBE_INSN_PAGE_SIZE(num_slots), GFP_KERNEL);
 	if (!kip)
 		goto out;

@@ -185,9 +187,11 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 		goto out;
 	}
 	INIT_LIST_HEAD(&kip->list);
-	memset(kip->slot_used, SLOT_CLEAN, slots_per_page(c));
-	kip->slot_used[0] = SLOT_USED;
+	/* nused must be set before accessing slot_used */
+	kip->nused = num_slots;
+	memset(kip->slot_used, SLOT_CLEAN, num_slots);
 	kip->nused = 1;
+	kip->slot_used[0] = SLOT_USED;
 	kip->ngarbage = 0;
 	kip->cache = c;
 	list_add_rcu(&kip->list, &c->pages);

-- 
2.47.0