Messages in this thread | | | From | Dmitry Vyukov <> | Date | Tue, 3 Sep 2013 18:41:16 +0400 | Subject | Out-of-bounds access in get_wchan (arch/x86/kernel/process_64.c) |
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Hi,
We are working on a memory error detector AddressSanitizer for Linux kernel (https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel), it can detect use-after-free and buffer-overflow errors.
Here is a new report from the tool:
[ 124.575597] ERROR: AddressSanitizer: heap-buffer-overflow on address ffff88002e280000 [ 124.576801] ffff88002e280000 is located 131938492886538 bytes to the left of 28857600-byte region [ffffffff81282e0a, ffffffff82e0830a) [ 124.578633] Accessed by thread T10915: [ 124.579295] inlined in describe_heap_address ./arch/x86/mm/asan/report.c:164 [ 124.579295] #0 ffffffff810dd277 in asan_report_error ./arch/x86/mm/asan/report.c:278 [ 124.580137] #1 ffffffff810dc6a0 in asan_check_region ./arch/x86/mm/asan/asan.c:37 [ 124.581050] #2 ffffffff810dd423 in __tsan_read8 ??:0 [ 124.581893] #3 ffffffff8107c093 in get_wchan ./arch/x86/kernel/process_64.c:444 [ 124.582763] #4 ffffffff81342108 in do_task_stat array.c:0 [ 124.583634] #5 ffffffff81342dcc in proc_tgid_stat ??:0 [ 124.584548] #6 ffffffff8133c984 in proc_single_show base.c:0 [ 124.585461] #7 ffffffff812d18cc in seq_read ./fs/seq_file.c:222 [ 124.586313] #8 ffffffff8129e503 in vfs_read ??:0 [ 124.587137] #9 ffffffff8129f800 in SyS_read ??:0 [ 124.587827] #10 ffffffff81929bf5 in sysenter_dispatch ./arch/x86/ia32/ia32entry.S:164 [ 124.588738] [ 124.588964] Allocated by thread T0: [ 124.592379] #4 ffffffff00000008 in __per_cpu_start ??:0 [ 124.593217] [ 124.593434] Shadow bytes around the buggy address: [ 124.594270] ffff88002e27fd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.595339] ffff88002e27fe00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.596453] ffff88002e27fe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.597466] ffff88002e27ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.598501] ffff88002e27ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.599629] =>ffff88002e280000:[fa]fa fa fa fa fa fa fa fa fa 00 00 00 00 00 00 [ 124.600873] ffff88002e280080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 [ 124.601892] ffff88002e280100: 00 fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa [ 124.603037] ffff88002e280180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa [ 124.604047] ffff88002e280200: fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd fd [ 124.605054] ffff88002e280280: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fa fa [ 124.605993] Shadow byte legend (one shadow byte represents 8 application bytes): [ 124.606958] Addressable: 00 [ 124.607483] Partially addressable: 01 02 03 04 05 06 07 [ 124.608219] Heap redzone: fa [ 124.608724] Heap kmalloc redzone: fb [ 124.609249] Freed heap region: fd [ 124.609753] Shadow gap: fe [ 124.610292] =========================================================================
Indeed, get_wchan ensures that fp<stack+THREAD_SIZE, but then dereferences fp+8:
434 if (fp < (unsigned long)stack || 435 fp >= (unsigned long)stack+THREAD_SIZE) 436 return 0; 437 ip = *(u64 *)(fp+8);
It must check that fp+8<stack+THREAD_SIZE. As far as I see, the bug can lead to garbage return values or in the worst case to crash.
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