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    Subject[PATCH 3.10 202/250] metag/usercopy: Fix alignment error checking
    Date
    From: James Hogan <james.hogan@imgtec.com>

    commit 2257211942bbbf6c798ab70b487d7e62f7835a1a upstream.

    Fix the error checking of the alignment adjustment code in
    raw_copy_from_user(), which mistakenly considers it safe to skip the
    error check when aligning the source buffer on a 2 or 4 byte boundary.

    If the destination buffer was unaligned it may have started to copy
    using byte or word accesses, which could well be at the start of a new
    (valid) source page. This would result in it appearing to have copied 1
    or 2 bytes at the end of the first (invalid) page rather than none at
    all.

    Fixes: 373cd784d0fc ("metag: Memory handling")
    Signed-off-by: James Hogan <james.hogan@imgtec.com>
    Cc: linux-metag@vger.kernel.org
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    ---
    arch/metag/lib/usercopy.c | 10 ++++------
    1 file changed, 4 insertions(+), 6 deletions(-)

    diff --git a/arch/metag/lib/usercopy.c b/arch/metag/lib/usercopy.c
    index b3ebfe9..a26c889 100644
    --- a/arch/metag/lib/usercopy.c
    +++ b/arch/metag/lib/usercopy.c
    @@ -830,6 +830,8 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
    if ((unsigned long) src & 1) {
    __asm_copy_from_user_1(dst, src, retn);
    n--;
    + if (retn)
    + goto copy_exception_bytes;
    }
    if ((unsigned long) dst & 1) {
    /* Worst case - byte copy */
    @@ -843,6 +845,8 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
    if (((unsigned long) src & 2) && n >= 2) {
    __asm_copy_from_user_2(dst, src, retn);
    n -= 2;
    + if (retn)
    + goto copy_exception_bytes;
    }
    if ((unsigned long) dst & 2) {
    /* Second worst case - word copy */
    @@ -854,12 +858,6 @@ unsigned long __copy_user_zeroing(void *pdst, const void __user *psrc,
    }
    }

    - /* We only need one check after the unalignment-adjustments,
    - because if both adjustments were done, either both or
    - neither reference had an exception. */
    - if (retn != 0)
    - goto copy_exception_bytes;
    -
    #ifdef USE_RAPF
    /* 64 bit copy loop */
    if (!(((unsigned long) src | (unsigned long) dst) & 7)) {
    --
    2.8.0.rc2.1.gbe9624a
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