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    Subject[PATCH AUTOSEL 4.19 17/26] dm table: don't copy from a NULL pointer in realloc_argv()
    Date
    From: Jerome Marchand <jmarchan@redhat.com>

    [ Upstream commit a0651926553cfe7992166432e418987760882652 ]

    For the first call to realloc_argv() in dm_split_args(), old_argv is
    NULL and size is zero. Then memcpy is called, with the NULL old_argv
    as the source argument and a zero size argument. AFAIK, this is
    undefined behavior and generates the following warning when compiled
    with UBSAN on ppc64le:

    In file included from ./arch/powerpc/include/asm/paca.h:19,
    from ./arch/powerpc/include/asm/current.h:16,
    from ./include/linux/sched.h:12,
    from ./include/linux/kthread.h:6,
    from drivers/md/dm-core.h:12,
    from drivers/md/dm-table.c:8:
    In function 'memcpy',
    inlined from 'realloc_argv' at drivers/md/dm-table.c:565:3,
    inlined from 'dm_split_args' at drivers/md/dm-table.c:588:9:
    ./include/linux/string.h:345:9: error: argument 2 null where non-null expected [-Werror=nonnull]
    return __builtin_memcpy(p, q, size);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
    drivers/md/dm-table.c: In function 'dm_split_args':
    ./include/linux/string.h:345:9: note: in a call to built-in function '__builtin_memcpy'

    Signed-off-by: Jerome Marchand <jmarchan@redhat.com>
    Signed-off-by: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/md/dm-table.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
    index c7fe4789c40e..34ab30dd5de9 100644
    --- a/drivers/md/dm-table.c
    +++ b/drivers/md/dm-table.c
    @@ -562,7 +562,7 @@ static char **realloc_argv(unsigned *size, char **old_argv)
    gfp = GFP_NOIO;
    }
    argv = kmalloc_array(new_size, sizeof(*argv), gfp);
    - if (argv) {
    + if (argv && old_argv) {
    memcpy(argv, old_argv, *size * sizeof(*argv));
    *size = new_size;
    }
    --
    2.20.1
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