Re: [PATCH] thinkpad-acpi: Avoid heap buffer overrun

[Michael Buesch <mb@bu3sch.de>]

On Tuesday 21 July 2009 12:16:17 Michael Buesch wrote:
> Avoid a heap buffer overrun triggered by an integer overflow of the userspace
> controlled "count" variable.
> If userspace passes in a "count" of (size_t)-1l, the kmalloc size will overflow
> to ((size_t)-1l + 2) = 1, so only one byte will be allocated. However, copy_from_user()
> will attempt to copy 0xFFFFFFFF (or 0xFFFFFFFFFFFFFFFF on 64bit) bytes to the buffer.
> 
> A possible testcase could look like this:
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <fcntl.h>
> 
> int main(int argc, char **argv)
> {
> 	int fd;
> 	char c;
> 
> 	if (argc != 2) {
> 		printf("Usage: %s /proc/acpi/ibm/filename\n", argv[0]);
> 		return 1;
> 	}
> 	fd = open(argv[1], O_RDWR);
> 	if (fd < 0) {
> 		printf("Could not open proc file\n");
> 		return 1;
> 	}
> 	write(fd, &c, (size_t)-1l);
> }
> 
> We avoid the integer overrun by putting an arbitrary limit on the count.
> PAGE_SIZE sounds like a sane limit.
> 
> Signed-off-by: Michael Buesch <mb@bu3sch.de>

Whoops, forgot
Cc: stable@kernel.org


-- 
Greetings, Michael.