BUG: KMSAN: uninit-value in kmsan_handle_dma #76

SunHao-0 · 2020-04-18T09:13:03Z

While fuzzing latest KMSAN-build with HEALER(syscall fuzzer, not published yet), uninit-value is found in kmsan_handle_dma. It seems KMSAN found bugs in itself.

Caused by this call sequence syscalls.txt.
With this crash msg.txt.
THE latest KMSAN is used with this config config.txt.

ramosian-glider · 2020-04-18T09:44:21Z

This may be a valid bug in the kernel,a as kmsan_handle_dma() just checks the memory it received.
In particular, this memory came from a kmalloc() call in elf_core_dump().
Not sure I'll be able to reproduce this bug using your syscall sequence, as it's neither C nor syzlang. What do I need to make it a valid C program?

In the meantime, you can add a memset after the kmalloc call in elf_core_dump() and overwrite the buffer with e.g. 0xAA. Then dump the memory in ata_qc_issue() and check if it's writing 0xAA's on disk.
(Chances also are that I'm handling disk writes incorrectly, and these uninit writes aren't actually happening).

SunHao-0 · 2020-04-18T10:03:03Z

It happened five times during fuzzing in 24-h. The syscall sequence is a valid C program without header files, so just include related headers and wrap syscalls in the main function is enough.
Pretty sure it's reproducible. Is it possible that this crash is caused by some other functions called by kmsan_handle_dma(), such as inline function? Thanks for replying.

ramosian-glider · 2020-04-18T10:17:48Z

Well, this is not a crash per se, it is a KMSAN report:

[ 1949.562864][ T3256] BUG: KMSAN: uninit-value in kmsan_handle_dma+0x9f/0xb0
...
[ 1949.568947][ T3256] kmsan_internal_check_memory+0x238/0x3d0
[ 1949.569644][ T3256] kmsan_handle_dma+0x9f/0xb0
[ 1949.570203][ T3256] kmsan_handle_dma_sg+0x35/0x50
[ 1949.570801][ T3256] ata_qc_issue+0xc71/0x1570
...
[ 1949.584854][ T3256] Uninit was stored to memory at:
[ 1949.585435][ T3256] kmsan_internal_chain_origin+0xad/0x130
[ 1949.586093][ T3256] kmsan_memcpy_memmove_metadata+0x262/0x2d0
[ 1949.586780][ T3256] kmsan_memcpy_metadata+0xb/0x10
[ 1949.587364][ T3256] __msan_memcpy+0x43/0x50
[ 1949.587876][ T3256] iov_iter_copy_from_user_atomic+0xb02/0x1510
[ 1949.588584][ T3256] generic_perform_write+0x499/0x9a0
[ 1949.589193][ T3256] ext4_buffered_write_iter+0x795/0xac0
[ 1949.589831][ T3256] ext4_file_write_iter+0x1330/0x2c60
[ 1949.590456][ T3256] __vfs_write+0xa5a/0xca0
[ 1949.590967][ T3256] __kernel_write+0x208/0x5f0
[ 1949.591507][ T3256] dump_emit+0x2ba/0x570
[ 1949.591998][ T3256] writenote+0x30c/0x4c0
[ 1949.592488][ T3256] elf_core_dump+0x6c49/0x8000
...
[ 1949.596382][ T3256] Uninit was created at:
[ 1949.596873][ T3256] kmsan_internal_poison_shadow+0x66/0xd0
[ 1949.597536][ T3256] kmsan_slab_alloc+0x8a/0xe0
[ 1949.598075][ T3256] __kmalloc+0x2c1/0x450
[ 1949.598566][ T3256] elf_core_dump+0x21dc/0x8000
[ 1949.599117][ T3256] do_coredump+0x3f74/0x56b0
[ 1949.599648][ T3256] get_signal+0xb36/0x32e0
[ 1949.600160][ T3256] do_signal+0x6f/0xe30
[ 1949.600646][ T3256] prepare_exit_to_usermode+0x2f0/0x520
[ 1949.601286][ T3256] swapgs_restore_regs_and_return_to_usermode+0x0/0x39
[ 1949.602069][ T3256] 
[ 1949.602341][ T3256] Bytes 2600-2647 of 4096 are uninitialized
[ 1949.603017][ T3256] Memory access of size 4096 starts at ffff999becb67000
[ 1949.603843][ T3256] =====================================================

So what presumably happens here is that elf_core_dump() allocates uninitialized memory, which is then written to the filesystem by __vfs_write(), and then asynchronously written to disk by ata_qc_issue().

If you add memset(0xAA) to the respective kmalloc call, you can even inspect the core dump file and search for 0xAA.

SunHao-0 · 2020-04-18T10:50:01Z

Thanks, got it. However, title of this kmsan report (uninit-value in kmsan_handle_dma+0x9f/0xb0) is misleading.

ramosian-glider · 2020-04-19T09:31:38Z

Actually, the bug can be triggered by a trivial crashing program:

int main() {
  volatile char *c = 0;
  (void)*c;
  return 0;
}

I'm going to send an upstream patch.

ramosian-glider · 2020-04-19T09:33:04Z

Please let me know how the Reported-by: tag should look like, otherwise I'll send with:

Reported-by: sam <sunhaoyl@outlook.com>

SunHao-0 · 2020-04-19T13:16:18Z

Please let me know how the Reported-by: tag should look like, otherwise I'll send with:

Reported-by: sam <sunhaoyl@outlook.com>

Thanks! That would be very nice of you.

KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Alexander Potapenko <glider@google.com> Reported-by: sam <sunhaoyl@outlook.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Kees Cook <keescook@chromium.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Alexander Potapenko <glider@google.com> Reported-by: sam <sunhaoyl@outlook.com> Acked-by: Kees Cook <keescook@chromium.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

In a core dump, copy_xstate_to_kernel() copies only enabled user xfeatures to a kernel buffer without touching areas for disabled xfeatures. However, those uninitialized areas may contain random data, which is then written to the core dump file and can be read by a non-privileged user. Fix it by clearing uninitialized areas. Link: google/kmsan#76 Link: https://lore.kernel.org/lkml/20200419100848.63472-1-glider@google.com/ Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Reported-by: sam <sunhaoyl@outlook.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Kees Cook <keescook@chromium.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Jann Horn <jannh@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Alexander Potapenko <glider@google.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: <stable@vger.kernel.org>

KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Alexander Potapenko <glider@google.com> Reported-by: sam <sunhaoyl@outlook.com> Acked-by: Kees Cook <keescook@chromium.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

…_core_info() KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Alexander Potapenko <glider@google.com> Reported-by: sam <sunhaoyl@outlook.com> Acked-by: Kees Cook <keescook@chromium.org> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit 1d60541 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit 1d605416fb7175e1adf094251466caa52093b413 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org> Change-Id: I247cd20b7d51612ed27d79424db0fa9318769bf6

[ Upstream commit 1d60541 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit 1d605416fb7175e1adf094251466caa52093b413 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org> Change-Id: I247cd20b7d51612ed27d79424db0fa9318769bf6

[ Upstream commit 1d60541 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit 1d605416fb7175e1adf094251466caa52093b413 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org> Change-Id: I247cd20b7d51612ed27d79424db0fa9318769bf6

[ Upstream commit 1d60541 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit 1d605416fb7175e1adf094251466caa52093b413 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>

[ Upstream commit 1d605416fb7175e1adf094251466caa52093b413 ] KMSAN reported uninitialized data being written to disk when dumping core. As a result, several kilobytes of kmalloc memory may be written to the core file and then read by a non-privileged user. Reported-by: sam <sunhaoyl@outlook.com> Signed-off-by: Alexander Potapenko <glider@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Kees Cook <keescook@chromium.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/r/20200419100848.63472-1-glider@google.com Link: google/kmsan#76 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org> Change-Id: I247cd20b7d51612ed27d79424db0fa9318769bf6

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BUG: KMSAN: uninit-value in kmsan_handle_dma #76

BUG: KMSAN: uninit-value in kmsan_handle_dma #76

SunHao-0 commented Apr 18, 2020

ramosian-glider commented Apr 18, 2020

SunHao-0 commented Apr 18, 2020

ramosian-glider commented Apr 18, 2020

SunHao-0 commented Apr 18, 2020

ramosian-glider commented Apr 19, 2020

ramosian-glider commented Apr 19, 2020 •

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SunHao-0 commented Apr 19, 2020

BUG: KMSAN: uninit-value in kmsan_handle_dma #76

BUG: KMSAN: uninit-value in kmsan_handle_dma #76

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SunHao-0 commented Apr 18, 2020

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ramosian-glider commented Apr 19, 2020

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