Messages in this thread Patch in this message | | | Date | Thu, 12 Nov 2020 10:35:46 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] lib: vsprintf: Avoid 32-bit truncation in vsscanf number parsing |
| |
On Thu, 12 Nov 2020 11:17:59 +0000 Richard Fitzgerald <rf@opensource.cirrus.com> wrote:
> Number conversion in vsscanf converts a whole string of digits and then > extracts the field width part from the converted value. The maximum run > of digits is limited by overflow. Conversion was using either > simple_strto[u]l or simple_strto[u]ll based on the 'L' qualifier. This > created a difference in truncation between builds where long is 32-bit > and builds where it is 64-bit. This especially affects parsing a run of > contiguous digits into separate fields - the maximum length of the run > is 16 digits if long is 64-bit but only 8 digits if long is 32-bits. > For example a conversion "%6x%6x" would convert both fields correctly if > long is 64-bit but not if long is 32-bit. > > It is undesirable for vsscanf to parse numbers differently depending on > the size of long on the target build. > > As simple_strto[u]l just calls simple_strto[u]ll anyway the conversion > is always 64-bit, and the result is manipulated as a u64, so this is an > avoidable behaviour difference between 32-bit and 64-bit builds. The > conversion can call simple_strto[u]ll directly and preserve the full > 64-bits that were parsed out of the string. > > Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com> > --- > lib/vsprintf.c | 8 ++------ > 1 file changed, 2 insertions(+), 6 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index 14c9a6af1b23..63b6cddfa7f7 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -3444,13 +3444,9 @@ int vsscanf(const char *buf, const char *fmt, va_list args) > break; > > if (is_sign) > - val.s = qualifier != 'L' ? > - simple_strtol(str, &next, base) : > - simple_strtoll(str, &next, base); > + val.s = simple_strtoll(str, &next, base); > else > - val.u = qualifier != 'L' ? > - simple_strtoul(str, &next, base) : > - simple_strtoull(str, &next, base); > + val.u = simple_strtoull(str, &next, base); > > if (field_width > 0 && next - str > field_width) { > if (base == 0)
It looks like this is fixing the symptom and not the disease. The real issue I see here is that vsscanf is not honoring the '6' of '%6x' here. It should only read the 6 characters then do the conversion, not the other way around! This looks to me that the design is of issue.
-- Steve
| |