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 <[email protected]>
Whoops, forgot
Cc: [email protected]
--
Greetings, Michael.
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