get_wchan() checks that fp is within stack bounds,
but then dereferences fp+8. This can crash kernel
or leak sensitive information. Also the function
operates on a potentially running stack, but does
not use READ_ONCE. As the result it can check that
one value is within stack bounds, but then deref
another value.
Fix the bounds check and use READ_ONCE for all
volatile data.
The bug was discovered with KASAN.
Signed-off-by: Dmitry Vyukov <dvyu...@google.com>
---
v2: Use "fp+sizeof(u64)" instead of "fp" in upper bound
comparison because we are going to read 8 bytes at fp.
As per Andrey Ryabinin comment.
FTR, here is the KASAN report:
[ 124.575597] ERROR: AddressSanitizer: heap-buffer-overflow on address
ffff88002e280000
[ 124.578633] Accessed by thread T10915:
[ 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]
[ 124.593434] 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]
=========================================================================
---
arch/x86/kernel/process_64.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 71d7849..0885eed 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -506,17 +506,19 @@ unsigned long get_wchan(struct task_struct *p)
if (!p || p == current || p->state == TASK_RUNNING)
return 0;
stack = (unsigned long)task_stack_page(p);
- if (p->thread.sp < stack || p->thread.sp >= stack+THREAD_SIZE)
+ /* The task can be already running at this point, so tread carefully. */
+ fp = READ_ONCE(p->thread.sp);
+ if (fp < stack || fp+sizeof(u64) > stack+THREAD_SIZE)
return 0;
- fp = *(u64 *)(p->thread.sp);
+ fp = READ_ONCE(*(u64 *)fp);
do {
if (fp < (unsigned long)stack ||
- fp >= (unsigned long)stack+THREAD_SIZE)
+ fp+8+sizeof(u64) > (unsigned long)stack+THREAD_SIZE)
return 0;
- ip = *(u64 *)(fp+8);
+ ip = READ_ONCE(*(u64 *)(fp+8));
if (!in_sched_functions(ip))
return ip;
- fp = *(u64 *)fp;
+ fp = READ_ONCE(*(u64 *)fp);
} while (count++ < 16);
return 0;
}
--
2.6.0.rc2.230.g3dd15c0
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