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    Subject[PATCH] fix stack memory content leak via UNAME26
    Calling uname() with the UNAME26 personality set allows a leak of kernel
    stack contents. This fixes it by initializing the stack buffer to zero,
    defensively calculating the length of copy_to_user() call, and making
    the len argument unsigned.

    CVE-2012-0957

    Reported-by: Brad Spengler <spender@grsecurity.net>
    Cc: stable@vger.kernel.org
    Cc: Andi Kleen <ak@linux.intel.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    ---
    kernel/sys.c | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    diff --git a/kernel/sys.c b/kernel/sys.c
    index c5cb5b9..6329092 100644
    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -1265,13 +1265,13 @@ DECLARE_RWSEM(uts_sem);
    * Work around broken programs that cannot handle "Linux 3.0".
    * Instead we map 3.x to 2.6.40+x, so e.g. 3.0 would be 2.6.40
    */
    -static int override_release(char __user *release, int len)
    +static int override_release(char __user *release, size_t len)
    {
    int ret = 0;
    - char buf[65];
    + char buf[65] = { 0 };
    + const char *rest = UTS_RELEASE;

    if (current->personality & UNAME26) {
    - char *rest = UTS_RELEASE;
    int ndots = 0;
    unsigned v;

    @@ -1283,7 +1283,9 @@ static int override_release(char __user *release, int len)
    rest++;
    }
    v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
    - snprintf(buf, len, "2.6.%u%s", v, rest);
    + snprintf(buf, sizeof(buf), "2.6.%u%s", v, rest);
    + if (sizeof(buf) < len)
    + len = sizeof(buf);
    ret = copy_to_user(release, buf, len);
    }
    return ret;
    --
    1.7.9.5

    --
    Kees Cook
    Chrome OS Security


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