Messages in this thread | | | Date | Wed, 20 May 2020 20:11:26 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH 13/20] maccess: always use strict semantics for probe_kernel_read |
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On Tue, 19 May 2020 15:44:42 +0200 Christoph Hellwig <hch@lst.de> wrote:
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c > index 2f6737cc53e6c..82da20e712507 100644 > --- a/kernel/trace/trace_kprobe.c > +++ b/kernel/trace/trace_kprobe.c > @@ -1208,7 +1208,13 @@ fetch_store_strlen(unsigned long addr) > u8 c; > > do { > - ret = probe_kernel_read(&c, (u8 *)addr + len, 1); > + if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) && > + (unsigned long)addr < TASK_SIZE) { > + ret = probe_user_read(&c, > + (__force u8 __user *)addr + len, 1); > + } else { > + ret = probe_kernel_read(&c, (u8 *)addr + len, 1); > + } > len++; > } while (c && ret == 0 && len < MAX_STRING_SIZE);
To avoid redundant check in the loop, we can use strnlen_user_nofault() out of the loop. Something like below.
... u8 c;
if (IS_ENABLED(CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE) && (unsigned long)addr < TASK_SIZE) { return strnlen_user_nofault((__force u8 __user *)addr, MAX_STRING_SIZE);
do { ret = probe_kernel_read(&c, (u8 *)addr + len, 1); len++; } while (c && ret == 0 && len < MAX_STRING_SIZE); ...
This must work because we must not have a string that continues across kernel space and user space.
Thank you,
-- Masami Hiramatsu <mhiramat@kernel.org>
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