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    Subject[PATCH 1/3] tracing: detect the string termination character when parsing user input string
    Date
    From: Changbin Du <changbin.du@intel.com>

    The usersapce can give a '\0' terminated C string or even has '\0' at the
    middle of input buffer. We need handle both these two cases correctly.

    Before this change, trace_get_user() will return a parsed string "\0" in
    below case. It is not expected (expects it skip all inputs) and cause the
    caller failed.

    open("/sys/kernel/debug/tracing//set_ftrace_pid", O_WRONLY|O_TRUNC) = 3
    write(3, " \0", 2) = -1 EINVAL (Invalid argument)

    This patch try to make the parser '\0' aware to fix such issue.

    Since the caller expects trace_get_user() to parse whole input buffer, so
    this patch treat '\0' as a separator as whitespace.

    Signed-off-by: Changbin Du <changbin.du@intel.com>
    ---
    kernel/trace/trace.c | 17 +++++++++++------
    1 file changed, 11 insertions(+), 6 deletions(-)

    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 2a8d8a2..18526a1 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -1194,9 +1194,14 @@ void trace_parser_put(struct trace_parser *parser)
    parser->buffer = NULL;
    }

    +static inline bool is_space_or_zero(char ch)
    +{
    + return isspace(ch) || !ch;
    +}
    +
    /*
    - * trace_get_user - reads the user input string separated by space
    - * (matched by isspace(ch))
    + * trace_get_user - reads the user input string separated by space or '\0'
    + * (matched by is_space_or_zero(ch))
    *
    * For each string found the 'struct trace_parser' is updated,
    * and the function returns.
    @@ -1228,7 +1233,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
    */
    if (!parser->cont) {
    /* skip white space */
    - while (cnt && isspace(ch)) {
    + while (cnt && is_space_or_zero(ch)) {
    ret = get_user(ch, ubuf++);
    if (ret)
    goto out;
    @@ -1237,7 +1242,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
    }

    /* only spaces were written */
    - if (isspace(ch)) {
    + if (is_space_or_zero(ch)) {
    *ppos += read;
    ret = read;
    goto out;
    @@ -1247,7 +1252,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
    }

    /* read the non-space input */
    - while (cnt && !isspace(ch)) {
    + while (cnt && !is_space_or_zero(ch)) {
    if (parser->idx < parser->size - 1)
    parser->buffer[parser->idx++] = ch;
    else {
    @@ -1262,7 +1267,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
    }

    /* We either got finished input or we have to wait for another call. */
    - if (isspace(ch)) {
    + if (is_space_or_zero(ch)) {
    parser->buffer[parser->idx] = 0;
    parser->cont = false;
    } else if (parser->idx < parser->size - 1) {
    --
    2.7.4
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