Re: [PATCH] virt-host-validate: Allow longer list of CPU flags

On Tue, Jul 23, 2024 at 12:41:31 +0200, Michal Privoznik wrote: > On various occasions, virt-host-validate parses /proc/cpuinfo to > learn about CPU flags (see virHostValidateGetCPUFlags()). It does > so, by reading the file line by line until the line with CPU > flags is reached. Then the line is split into individual flags > (using space as a delimiter) and the list of flags is then > iterated over. > > This works, except for cases when the line with CPU flags is too > long. Problem is - the line is capped at 1024 bytes and on newer > CPUs (and newer kernels), the line can be significantly longer. > I've seen a line that's ~1200 characters long (with 164 flags > reported). > > Switch to unbounded read from the file (getline()). > > Resolves: https://issues.redhat.com/browse/RHEL-39969 > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > --- > tools/virt-host-validate-common.c | 16 ++++------------ > 1 file changed, 4 insertions(+), 12 deletions(-) > > diff --git a/tools/virt-host-validate-common.c b/tools/virt-host-validate-common.c > index 591143c24d..e5fa6606d2 100644 > --- a/tools/virt-host-validate-common.c > +++ b/tools/virt-host-validate-common.c > @@ -106,21 +106,19 @@ virBitmap *virHostValidateGetCPUFlags(void) > { > FILE *fp; > virBitmap *flags = NULL; > + g_autofree char *line = NULL; > + size_t linelen = 0; > > if (!(fp = fopen("/proc/cpuinfo", "r"))) > return NULL; > > flags = virBitmapNew(VIR_HOST_VALIDATE_CPU_FLAG_LAST); > > - do { > - char line[1024]; > + while (getline(&line, &linelen, fp) > 0) { > char *start; > g_auto(GStrv) tokens = NULL; > GStrv next; > > - if (!fgets(line, sizeof(line), fp)) > - break; > - > /* The line we're interested in is marked differently depending > * on the architecture, so check possible prefixes */ > if (!STRPREFIX(line, "flags") && > @@ -129,12 +127,6 @@ virBitmap *virHostValidateGetCPUFlags(void) > !STRPREFIX(line, "facilities")) > continue; > > - /* fgets() includes the trailing newline in the output buffer, > - * so we need to clean that up ourselves. We can safely access > - * line[strlen(line) - 1] because the checks above would cause > - * us to skip empty strings */ > - line[strlen(line) - 1] = '\0'; > - getline() also includes the trailing newline in the buffer (as long as there is any newline) and thus we still need to drop it. We just don't need to call strlen to compute the length. Although I would suggest using a little bit more robust code instead of describing the existing code is safe...

if (linelen > 1 && line[linelen - 1] == '\n') line[linelen - 1] = '\0';