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isdn/capi: check message length in capi_write()

syzbot reported: BUG: KMSAN: uninit-value in capi_write+0x791/0xa90 drivers/isdn/capi/capi.c:700 CPU: 0 PID: 10025 Comm: syz-executor379 Not tainted 4.20.0-rc7+ #2 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x173/0x1d0 lib/dump_stack.c:113 kmsan_report+0x12e/0x2a0 mm/kmsan/kmsan.c:613 __msan_warning+0x82/0xf0 mm/kmsan/kmsan_instr.c:313 capi_write+0x791/0xa90 drivers/isdn/capi/capi.c:700 do_loop_readv_writev fs/read_write.c:703 [inline] do_iter_write+0x83e/0xd80 fs/read_write.c:961 vfs_writev fs/read_write.c:1004 [inline] do_writev+0x397/0x840 fs/read_write.c:1039 __do_sys_writev fs/read_write.c:1112 [inline] __se_sys_writev+0x9b/0xb0 fs/read_write.c:1109 __x64_sys_writev+0x4a/0x70 fs/read_write.c:1109 do_syscall_64+0xbc/0xf0 arch/x86/entry/common.c:291 entry_SYSCALL_64_after_hwframe+0x63/0xe7 [...] The problem is that capi_write() is reading past the end of the message. Fix it by checking the message's length in the needed places.

Eric Biggers committed 7 years ago

Commit fe163e51 parent 1c2977c2 files · +10 −1Browse files

Unified · Split

2 files
  1. drivers/isdn/capi/capi.c +9 −1
  2. include/uapi/linux/isdn/capicmd.h +1 −0
drivers/isdn/capi/capi.c+9−1
@@ -688,6 +688,9 @@ capi_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos · 687 unmodified lines
688 if (!cdev->ap.applid)688 if (!cdev->ap.applid)
689 return -ENODEV;689 return -ENODEV;
690 690
691 if (count < CAPIMSG_BASELEN)
692 return -EINVAL;
693
691 skb = alloc_skb(count, GFP_USER);694 skb = alloc_skb(count, GFP_USER);
692 if (!skb)695 if (!skb)
693 return -ENOMEM;696 return -ENOMEM;
@@ -698,7 +701,8 @@ capi_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos · 4 unmodified lines
698 }701 }
699 mlen = CAPIMSG_LEN(skb->data);702 mlen = CAPIMSG_LEN(skb->data);
700 if (CAPIMSG_CMD(skb->data) == CAPI_DATA_B3_REQ) {703 if (CAPIMSG_CMD(skb->data) == CAPI_DATA_B3_REQ) {
701 if ((size_t)(mlen + CAPIMSG_DATALEN(skb->data)) != count) {704 if (count < CAPI_DATA_B3_REQ_LEN ||
705 (size_t)(mlen + CAPIMSG_DATALEN(skb->data)) != count) {
702 kfree_skb(skb);706 kfree_skb(skb);
703 return -EINVAL;707 return -EINVAL;
704 }708 }
@@ -711,6 +715,10 @@ capi_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos · 6 unmodified lines
711 CAPIMSG_SETAPPID(skb->data, cdev->ap.applid);715 CAPIMSG_SETAPPID(skb->data, cdev->ap.applid);
712 716
713 if (CAPIMSG_CMD(skb->data) == CAPI_DISCONNECT_B3_RESP) {717 if (CAPIMSG_CMD(skb->data) == CAPI_DISCONNECT_B3_RESP) {
718 if (count < CAPI_DISCONNECT_B3_RESP_LEN) {
719 kfree_skb(skb);
720 return -EINVAL;
721 }
714 mutex_lock(&cdev->lock);722 mutex_lock(&cdev->lock);
715 capincci_free(cdev, CAPIMSG_NCCI(skb->data));723 capincci_free(cdev, CAPIMSG_NCCI(skb->data));
716 mutex_unlock(&cdev->lock);724 mutex_unlock(&cdev->lock);
include/uapi/linux/isdn/capicmd.h+1−0
@@ -16,6 +16,7 @@ · 15 unmodified lines
16#define CAPI_MSG_BASELEN 816#define CAPI_MSG_BASELEN 8
17#define CAPI_DATA_B3_REQ_LEN (CAPI_MSG_BASELEN+4+4+2+2+2)17#define CAPI_DATA_B3_REQ_LEN (CAPI_MSG_BASELEN+4+4+2+2+2)
18#define CAPI_DATA_B3_RESP_LEN (CAPI_MSG_BASELEN+4+2)18#define CAPI_DATA_B3_RESP_LEN (CAPI_MSG_BASELEN+4+2)
19#define CAPI_DISCONNECT_B3_RESP_LEN (CAPI_MSG_BASELEN+4)
19 20
20/*----- CAPI commands -----*/21/*----- CAPI commands -----*/
21#define CAPI_ALERT 0x0122#define CAPI_ALERT 0x01