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    Subject[PATCH 4.14 068/167] selftests/x86: Clean up and document sscanf() usage
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Dominik Brodowski <linux@dominikbrodowski.net>

    commit d8e92de8ef952bed88c56c7a44c02d8dcae0984e upstream.

    Replace a couple of magically connected buffer length literal constants with
    a common definition that makes their relationship obvious. Also document
    why our sscanf() usage is safe.

    No intended functional changes.

    Suggested-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
    Cc: Andrew Lutomirski <luto@kernel.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-kselftest@vger.kernel.org
    Cc: shuah@kernel.org
    Link: http://lkml.kernel.org/r/20180211205924.GA23210@light.dominikbrodowski.net
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    tools/testing/selftests/x86/test_vdso.c | 11 ++++++++---
    tools/testing/selftests/x86/test_vsyscall.c | 11 ++++++++---
    2 files changed, 16 insertions(+), 6 deletions(-)

    --- a/tools/testing/selftests/x86/test_vdso.c
    +++ b/tools/testing/selftests/x86/test_vdso.c
    @@ -26,6 +26,9 @@
    # endif
    #endif

    +/* max length of lines in /proc/self/maps - anything longer is skipped here */
    +#define MAPS_LINE_LEN 128
    +
    int nerrs = 0;

    typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
    @@ -37,17 +40,19 @@ static void *vsyscall_getcpu(void)
    {
    #ifdef __x86_64__
    FILE *maps;
    - char line[128];
    + char line[MAPS_LINE_LEN];
    bool found = false;

    maps = fopen("/proc/self/maps", "r");
    if (!maps) /* might still be present, but ignore it here, as we test vDSO not vsyscall */
    return NULL;

    - while (fgets(line, sizeof(line), maps)) {
    + while (fgets(line, MAPS_LINE_LEN, maps)) {
    char r, x;
    void *start, *end;
    - char name[128];
    + char name[MAPS_LINE_LEN];
    +
    + /* sscanf() is safe here as strlen(name) >= strlen(line) */
    if (sscanf(line, "%p-%p %c-%cp %*x %*x:%*x %*u %s",
    &start, &end, &r, &x, name) != 5)
    continue;
    --- a/tools/testing/selftests/x86/test_vsyscall.c
    +++ b/tools/testing/selftests/x86/test_vsyscall.c
    @@ -33,6 +33,9 @@
    # endif
    #endif

    +/* max length of lines in /proc/self/maps - anything longer is skipped here */
    +#define MAPS_LINE_LEN 128
    +
    static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
    int flags)
    {
    @@ -98,7 +101,7 @@ static int init_vsys(void)
    #ifdef __x86_64__
    int nerrs = 0;
    FILE *maps;
    - char line[128];
    + char line[MAPS_LINE_LEN];
    bool found = false;

    maps = fopen("/proc/self/maps", "r");
    @@ -108,10 +111,12 @@ static int init_vsys(void)
    return 0;
    }

    - while (fgets(line, sizeof(line), maps)) {
    + while (fgets(line, MAPS_LINE_LEN, maps)) {
    char r, x;
    void *start, *end;
    - char name[128];
    + char name[MAPS_LINE_LEN];
    +
    + /* sscanf() is safe here as strlen(name) >= strlen(line) */
    if (sscanf(line, "%p-%p %c-%cp %*x %*x:%*x %*u %s",
    &start, &end, &r, &x, name) != 5)
    continue;

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