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    Subject[ 11/42] kernel/sys.c: fix stack memory content leak via UNAME26
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Kees Cook <keescook@chromium.org>

    commit 2702b1526c7278c4d65d78de209a465d4de2885e upstream.

    Calling uname() with the UNAME26 personality set allows a leak of kernel
    stack contents. This fixes it by defensively calculating the length of
    copy_to_user() call, making the len argument unsigned, and initializing
    the stack buffer to zero (now technically unneeded, but hey, overkill).

    CVE-2012-0957

    Reported-by: PaX Team <pageexec@freemail.hu>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: PaX Team <pageexec@freemail.hu>
    Cc: Brad Spengler <spender@grsecurity.net>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    kernel/sys.c | 12 +++++++-----
    1 file changed, 7 insertions(+), 5 deletions(-)

    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -1180,15 +1180,16 @@ 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];

    if (current->personality & UNAME26) {
    - char *rest = UTS_RELEASE;
    + const char *rest = UTS_RELEASE;
    + char buf[65] = { 0 };
    int ndots = 0;
    unsigned v;
    + size_t copy;

    while (*rest) {
    if (*rest == '.' && ++ndots >= 3)
    @@ -1198,8 +1199,9 @@ static int override_release(char __user
    rest++;
    }
    v = ((LINUX_VERSION_CODE >> 8) & 0xff) + 40;
    - snprintf(buf, len, "2.6.%u%s", v, rest);
    - ret = copy_to_user(release, buf, len);
    + copy = min(sizeof(buf), max_t(size_t, 1, len));
    + copy = scnprintf(buf, copy, "2.6.%u%s", v, rest);
    + ret = copy_to_user(release, buf, copy + 1);
    }
    return ret;
    }



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