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    Subject[PATCH][GIT PULL] tracing: Sanitize value returned from write(trace_marker, "...", len)
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    Ingo,

    I had this sitting in my quilt queue, and did not realize I never
    committed it. This is on top of my previous two pull requests.

    Thanks,

    -- Steve

    Please pull the latest tip/perf/urgent-3 tree, which can be found at:

    git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
    tip/perf/urgent-3


    Marcin Slusarz (1):
    tracing: Sanitize value returned from write(trace_marker, "...", len)

    ----
    kernel/trace/trace.c | 11 ++++++++---
    1 files changed, 8 insertions(+), 3 deletions(-)
    ---------------------------
    commit 1aa54bca6ee0d07ebcafb8ca8074b624d80724aa
    Author: Marcin Slusarz <marcin.slusarz@gmail.com>
    Date: Wed Jul 28 01:18:01 2010 +0200

    tracing: Sanitize value returned from write(trace_marker, "...", len)

    When userspace code writes non-new-line-terminated string to trace_marker
    file, write handler appends new-line and returns number of bytes written
    to trace buffer, so
    write(fd, "abc", 3) will return 4

    That's unexpected and unfortunately it confuses glibc's fprintf function.

    Example:
    int main() {
    fprintf(stderr, "abc");
    return 0;
    }

    $ gcc test.c -o test
    $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer
    $ ./test 2>/sys/kernel/debug/tracing/trace_marker

    results in infinite loop:
    write(fd, "abc", 3) = 4
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    write(fd, "", 1) = 0
    (...)

    ...and kernel trace buffer full of empty markers.

    Fix it by sanitizing write return value.

    Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
    LKML-Reference: <20100727231801.GB2826@joi.lan>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 086d363..88b42d1 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -3498,6 +3498,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
    size_t cnt, loff_t *fpos)
    {
    char *buf;
    + size_t written;

    if (tracing_disabled)
    return -EINVAL;
    @@ -3519,11 +3520,15 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
    } else
    buf[cnt] = '\0';

    - cnt = mark_printk("%s", buf);
    + written = mark_printk("%s", buf);
    kfree(buf);
    - *fpos += cnt;
    + *fpos += written;

    - return cnt;
    + /* don't tell userspace we wrote more - it might confuse them */
    + if (written > cnt)
    + written = cnt;
    +
    + return written;
    }

    static int tracing_clock_show(struct seq_file *m, void *v)



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