On 8/27/15 3:34 PM, David Miller wrote:
From: Alexei Starovoitov <a...@plumgrid.com> Date: Wed, 26 Aug 2015 23:26:59 -0700+/* similar to strncpy_from_user() but with extra checks */ +static void probe_read_string(char *buf, int size, long unsafe_ptr) +{ + char dst[4]; + int i = 0; + + size--; + for (;;) { + if (probe_kernel_read(dst, (void *) unsafe_ptr, 4)) + break;I don't think this does the right thing when the string is not a multiple of 3 and ends at the last byte of a page that ends a valid region of kernel memory. Seeing this kind of error makes me skeptical to the overall value of optimizing this :-/
I've considered the case when first two bytes are valid, but the other two are in a different page. In such case the probe_read_string() will trim the string and won't be printing these two valid bytes. I think that's very rare, so I'm picking higher performance for common case. The strings over > 64 bytes also will be trimmed to 64. It's a debugging facility, so I felt that's ok. Fair or you still think it should be per byte copy? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
