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    Subject[PATCH 4.14 162/176] sparc32: fix a user-triggerable oops in clear_user()
    Date
    From: Al Viro <viro@zeniv.linux.org.uk>

    commit 7780918b36489f0b2f9a3749d7be00c2ceaec513 upstream.

    Back in 2.1.29 the clear_user() guts (__bzero()) had been merged
    with memset(). Unfortunately, while all exception handlers had been
    copied, one of the exception table entries got lost. As the result,
    clear_user() starting at 128*n bytes before the end of page and
    spanning between 8 and 127 bytes into the next page would oops when
    the second page is unmapped. It's trivial to reproduce - all
    it takes is

    main()
    {
    int fd = open("/dev/zero", O_RDONLY);
    char *p = mmap(NULL, 16384, PROT_READ|PROT_WRITE,
    MAP_PRIVATE|MAP_ANON, -1, 0);
    munmap(p + 8192, 8192);
    read(fd, p + 8192 - 128, 192);
    }

    which had been oopsing since March 1997. Says something about
    the quality of test coverage... ;-/ And while today sparc32 port
    is nearly dead, back in '97 it had been very much alive; in fact,
    sparc64 had only been in mainline for 3 months by that point...

    Cc: stable@kernel.org
    Fixes: v2.1.29
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/sparc/lib/memset.S | 1 +
    1 file changed, 1 insertion(+)

    --- a/arch/sparc/lib/memset.S
    +++ b/arch/sparc/lib/memset.S
    @@ -142,6 +142,7 @@ __bzero:
    ZERO_LAST_BLOCKS(%o0, 0x48, %g2)
    ZERO_LAST_BLOCKS(%o0, 0x08, %g2)
    13:
    + EXT(12b, 13b, 21f)
    be 8f
    andcc %o1, 4, %g0


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