• Rasmus Villemoes's avatar
    lib/string_helpers.c: change semantics of string_escape_mem · 41416f23
    Rasmus Villemoes authored
    The current semantics of string_escape_mem are inadequate for one of its
    current users, vsnprintf().  If that is to honour its contract, it must
    know how much space would be needed for the entire escaped buffer, and
    string_escape_mem provides no way of obtaining that (short of allocating a
    large enough buffer (~4 times input string) to let it play with, and
    that's definitely a big no-no inside vsnprintf).
    
    So change the semantics for string_escape_mem to be more snprintf-like:
    Return the size of the output that would be generated if the destination
    buffer was big enough, but of course still only write to the part of dst
    it is allowed to, and (contrary to snprintf) don't do '\0'-termination.
    It is then up to the caller to detect whether output was truncated and to
    append a '\0' if desired.  Also, we must output partial escape sequences,
    otherwise a call such as snprintf(buf, 3, "%1pE", "\123") would cause
    printf to write a \0 to buf[2] but leaving buf[0] and buf[1] with whatever
    they previously contained.
    
    This also fixes a bug in the escaped_string() helper function, which used
    to unconditionally pass a length of "end-buf" to string_escape_mem();
    since the latter doesn't check osz for being insanely large, it would
    happily write to dst.  For example, kasprintf(GFP_KERNEL, "something and
    then %pE", ...); is an easy way to trigger an oops.
    
    In test-string_helpers.c, the -ENOMEM test is replaced with testing for
    getting the expected return value even if the buffer is too small.  We
    also ensure that nothing is written (by relying on a NULL pointer deref)
    if the output size is 0 by passing NULL - this has to work for
    kasprintf("%pE") to work.
    
    In net/sunrpc/cache.c, I think qword_add still has the same semantics.
    Someone should definitely double-check this.
    
    In fs/proc/array.c, I made the minimum possible change, but longer-term it
    should stop poking around in seq_file internals.
    
    [andriy.shevchenko@linux.intel.com: simplify qword_add]
    [andriy.shevchenko@linux.intel.com: add missed curly braces]
    Signed-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
    Acked-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    41416f23
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