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SubjectRe: [PATCH] VFS: Sanity check mount flags passed to change_mnt_propagation()
On Sat, Aug 28, 2010 at 04:57:07AM -0600, Matthew Wilcox wrote:
> > Didn't read surrounding code, but is that supposed to be '||'?
> >
> > Otherwise the case where only a single non-propagation flag is
> > set no longer returns 0...
>
> Val's original code returned 0 as failure. So a single non-propagation
> flag set shouldn't return 0.

Not to belabor the point -- but her original code did return zero in
that case (2nd assertion fails):

#include <linux/fs.h>
#include <stdio.h>
#include <assert.h>

#define hweight32 dumb_hweight32

int dumb_hweight32(int a)
{
int i;
int weight = 0;

for (i=0; i < 32; i++)
weight += !!(a & (1 << i));

return weight;
}

static int flags_to_propagation_type(int flags) {
int type = flags & ~MS_REC;

/* Fail if any non-propagation flags are set */
if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
return 0;
/* Only one propagation flag should be set */
if (((type & (MS_SHARED)) && (type & ~MS_SHARED)) ||
((type & (MS_PRIVATE)) && (type & ~MS_PRIVATE)) ||
((type & (MS_SLAVE)) && (type & ~MS_SLAVE)) ||
((type & (MS_UNBINDABLE)) && (type & ~MS_UNBINDABLE)))
return 0;
return type;
}

static int flags_to_propagation_type_2(int flags) {
int type = flags & ~MS_REC;

/* Only one propagation flag should be set, and no others */
if (hweight32(type) != 1 &&
(type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE)))
return 0;

return type;
}

int main(int argc, char *argv[])
{
int mytype = MS_RDONLY;

assert(flags_to_propagation_type(mytype) == 0);
assert(flags_to_propagation_type_2(mytype) == 0);
}

--
Bob Copeland %% www.bobcopeland.com



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