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.
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| @@ -16,6 +16,7 @@ · 15 unmodified lines | ||
| 16 | 16 | #define CAPI_MSG_BASELEN 8 |
| 17 | 17 | #define CAPI_DATA_B3_REQ_LEN (CAPI_MSG_BASELEN+4+4+2+2+2) |
| 18 | 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 | 21 | /*----- CAPI commands -----*/ |
| 21 | 22 | #define CAPI_ALERT 0x01 |