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    Subject[PATCH 2/4] tracing: Replace typecasted void pointer in set_ftrace_filter code
    From: Steven Rostedt <srostedt@redhat.com>

    The set_ftrace_filter uses seq_file and reads from two lists. The
    pointer returned by t_next() can either be of type struct dyn_ftrace
    or struct ftrace_func_probe. If there is a bug (there was one)
    the wrong pointer may be used and the reference can cause an oops.

    This patch makes t_next() and friends only return the iterator structure
    which now has a pointer of type struct dyn_ftrace and struct
    ftrace_func_probe. The t_show() can now test if the pointer is NULL or
    not and if the pointer exists, it is guaranteed to be of the correct type.

    Now if there's a bug, only wrong data will be shown but not an oops.

    Cc: Chris Wright <chrisw@sous-sol.org>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    kernel/trace/ftrace.c | 67 +++++++++++++++++++++++++++++++++---------------
    1 files changed, 46 insertions(+), 21 deletions(-)

    diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
    index 585ea27..c8db0db 100644
    --- a/kernel/trace/ftrace.c
    +++ b/kernel/trace/ftrace.c
    @@ -1368,25 +1368,29 @@ enum {
    #define FTRACE_BUFF_MAX (KSYM_SYMBOL_LEN+4) /* room for wildcards */

    struct ftrace_iterator {
    - loff_t func_pos;
    - struct ftrace_page *pg;
    - int hidx;
    - int idx;
    - unsigned flags;
    - struct trace_parser parser;
    + loff_t func_pos;
    + struct ftrace_page *pg;
    + struct dyn_ftrace *func;
    + struct ftrace_func_probe *probe;
    + struct trace_parser parser;
    + int hidx;
    + int idx;
    + unsigned flags;
    };

    static void *
    -t_hash_next(struct seq_file *m, void *v, loff_t *pos)
    +t_hash_next(struct seq_file *m, loff_t *pos)
    {
    struct ftrace_iterator *iter = m->private;
    - struct hlist_node *hnd = v;
    + struct hlist_node *hnd = NULL;
    struct hlist_head *hhd;

    WARN_ON(!(iter->flags & FTRACE_ITER_HASH));

    (*pos)++;

    + if (iter->probe)
    + hnd = &iter->probe->node;
    retry:
    if (iter->hidx >= FTRACE_FUNC_HASHSIZE)
    return NULL;
    @@ -1409,7 +1413,12 @@ t_hash_next(struct seq_file *m, void *v, loff_t *pos)
    }
    }

    - return hnd;
    + if (WARN_ON_ONCE(!hnd))
    + return NULL;
    +
    + iter->probe = hlist_entry(hnd, struct ftrace_func_probe, node);
    +
    + return iter;
    }

    static void *t_hash_start(struct seq_file *m, loff_t *pos)
    @@ -1428,19 +1437,24 @@ static void *t_hash_start(struct seq_file *m, loff_t *pos)

    iter->hidx = 0;
    for (l = 0; l <= (*pos - iter->func_pos); ) {
    - p = t_hash_next(m, p, &l);
    + p = t_hash_next(m, &l);
    if (!p)
    break;
    }
    - return p;
    + if (!p)
    + return NULL;
    +
    + return iter;
    }

    -static int t_hash_show(struct seq_file *m, void *v)
    +static int
    +t_hash_show(struct seq_file *m, struct ftrace_iterator *iter)
    {
    struct ftrace_func_probe *rec;
    - struct hlist_node *hnd = v;

    - rec = hlist_entry(hnd, struct ftrace_func_probe, node);
    + rec = iter->probe;
    + if (WARN_ON_ONCE(!rec))
    + return -EIO;

    if (rec->ops->print)
    return rec->ops->print(m, rec->ip, rec->ops, rec->data);
    @@ -1461,7 +1475,7 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
    struct dyn_ftrace *rec = NULL;

    if (iter->flags & FTRACE_ITER_HASH)
    - return t_hash_next(m, v, pos);
    + return t_hash_next(m, pos);

    (*pos)++;

    @@ -1495,7 +1509,12 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
    }
    }

    - return rec;
    + if (!rec)
    + return NULL;
    +
    + iter->func = rec;
    +
    + return iter;
    }

    static void *t_start(struct seq_file *m, loff_t *pos)
    @@ -1530,10 +1549,14 @@ static void *t_start(struct seq_file *m, loff_t *pos)
    break;
    }

    - if (!p && iter->flags & FTRACE_ITER_FILTER)
    - return t_hash_start(m, pos);
    + if (!p) {
    + if (iter->flags & FTRACE_ITER_FILTER)
    + return t_hash_start(m, pos);

    - return p;
    + return NULL;
    + }
    +
    + return iter;
    }

    static void t_stop(struct seq_file *m, void *p)
    @@ -1544,16 +1567,18 @@ static void t_stop(struct seq_file *m, void *p)
    static int t_show(struct seq_file *m, void *v)
    {
    struct ftrace_iterator *iter = m->private;
    - struct dyn_ftrace *rec = v;
    + struct dyn_ftrace *rec;

    if (iter->flags & FTRACE_ITER_HASH)
    - return t_hash_show(m, v);
    + return t_hash_show(m, iter);

    if (iter->flags & FTRACE_ITER_PRINTALL) {
    seq_printf(m, "#### all functions enabled ####\n");
    return 0;
    }

    + rec = iter->func;
    +
    if (!rec)
    return 0;

    --
    1.7.1



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