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SubjectRe: [BUG] libmount misparses mountinfo on Linux v2.6.39-rc1
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On Fri, 1 Apr 2011, Karel Zak wrote:
> On Fri, Apr 01, 2011 at 10:45:48AM +0200, Miklos Szeredi wrote:
> > On Fri, 01 Apr 2011, Aneesh Kumar K. V wrote:
> > > On Thu, 31 Mar 2011 22:24:01 +0200, victor.vde@gmail.com wrote:
> > > > /proc/self/mountinfo on Linux v2.6.39-rc1 includes the UUID of ext4
> > > > and ext3 mounts, for example:
> > > >
> > > > 15 1 8:3 / / rw,noatime uuid:c645234d-9756-4d84-825e-6fe999252a34 - ext4 /dev/sda3 rw,user_xattr,acl,barrier=1,data=ordered
> > > >
> > > > It seems the hyphens in the uuid confuse the parser
> > > > mnt_parse_mountinfo_line in tab_parse.c of libmount in util-linux.
> > >
> > > shouldn't the parser look for " " followed by "-" followed by " " as the
> > > field seperator ?
> > >
> > > I am adding Miklos and Ram Pai to CC to check whether the kernel or the libmount
> > > should be fixed ?
> >
> > I think libmount should be fixed, though there is always the question
> > of backward compatibility.
>
> The parser uses
>
> rc = sscanf(s, "%u " /* (1) id */
> "%u " /* (2) parent */
> "%u:%u " /* (3) maj:min */
> "%ms " /* (4) mountroot */
> "%ms " /* (5) target */
> "%ms" /* (6) vfs options (fs-independent) */
> "%*[^-]" /* (7) optional fields */

So this says, "skip everything up to the first hyphen", even though
the rule might be better expressed as "skip all space delimited words
up to the first standalone hyphen". I guess that's not possible to
express with a scanf expression, though.

> "- " /* (8) separator */
> "%ms " /* (9) FS type */
> "%ms " /* (10) source */
> "%ms", /* (11) fs options (fs specific) */
>
> note that almost the same code is in systemd.
>
> > However I don't see how the kernel could be fixed, given that libmount
> > doesn't seem to parse escape sequences (e.g. "\040" for space), which
> > it also should.
>
> It calls unmangle_string() for all fields, so all sequences should be
> decoded.

Okay, so the kernel can simply escape the troublesome hyphens, which
would make the human parsing of /proc/pid/mountinfo more difficult but
at least would fix compatibility with util-linux's parser.

Thanks,
Miklos


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