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    Subject[PATCH AUTOSEL for 4.15 142/189] firmware: dmi_scan: Fix handling of empty DMI strings
    Date
    From: Jean Delvare <jdelvare@suse.de>

    [ Upstream commit a7770ae194569e96a93c48aceb304edded9cc648 ]

    The handling of empty DMI strings looks quite broken to me:
    * Strings from 1 to 7 spaces are not considered empty.
    * True empty DMI strings (string index set to 0) are not considered
    empty, and result in allocating a 0-char string.
    * Strings with invalid index also result in allocating a 0-char
    string.
    * Strings starting with 8 spaces are all considered empty, even if
    non-space characters follow (sounds like a weird thing to do, but
    I have actually seen occurrences of this in DMI tables before.)
    * Strings which are considered empty are reported as 8 spaces,
    instead of being actually empty.

    Some of these issues are the result of an off-by-one error in memcmp,
    the rest is incorrect by design.

    So let's get it square: missing strings and strings made of only
    spaces, regardless of their length, should be treated as empty and
    no memory should be allocated for them. All other strings are
    non-empty and should be allocated.

    Signed-off-by: Jean Delvare <jdelvare@suse.de>
    Fixes: 79da4721117f ("x86: fix DMI out of memory problems")
    Cc: Parag Warudkar <parag.warudkar@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/firmware/dmi_scan.c | 22 +++++++++-------------
    1 file changed, 9 insertions(+), 13 deletions(-)

    diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
    index 783041964439..e8db9659a36b 100644
    --- a/drivers/firmware/dmi_scan.c
    +++ b/drivers/firmware/dmi_scan.c
    @@ -18,7 +18,7 @@ EXPORT_SYMBOL_GPL(dmi_kobj);
    * of and an antecedent to, SMBIOS, which stands for System
    * Management BIOS. See further: http://www.dmtf.org/standards
    */
    -static const char dmi_empty_string[] = " ";
    +static const char dmi_empty_string[] = "";

    static u32 dmi_ver __initdata;
    static u32 dmi_len;
    @@ -44,25 +44,21 @@ static int dmi_memdev_nr;
    static const char * __init dmi_string_nosave(const struct dmi_header *dm, u8 s)
    {
    const u8 *bp = ((u8 *) dm) + dm->length;
    + const u8 *nsp;

    if (s) {
    - s--;
    - while (s > 0 && *bp) {
    + while (--s > 0 && *bp)
    bp += strlen(bp) + 1;
    - s--;
    - }
    -
    - if (*bp != 0) {
    - size_t len = strlen(bp)+1;
    - size_t cmp_len = len > 8 ? 8 : len;

    - if (!memcmp(bp, dmi_empty_string, cmp_len))
    - return dmi_empty_string;
    + /* Strings containing only spaces are considered empty */
    + nsp = bp;
    + while (*nsp == ' ')
    + nsp++;
    + if (*nsp != '\0')
    return bp;
    - }
    }

    - return "";
    + return dmi_empty_string;
    }

    static const char * __init dmi_string(const struct dmi_header *dm, u8 s)
    --
    2.15.1
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