Messages in this thread Patch in this message | | | From | Or Cohen <> | Date | Tue, 5 Nov 2019 01:03:23 -0800 | Subject | Re: Bug report - slab-out-of-bounds in vcs_scr_readw |
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@Nicolas Pitre - I agree with you, "vcs_size" may return a negative error code, so the patch is correct but as @jslaby@suse.com said it won't fix the issue. In my debugging session, "vcs_size" returns a positive integer ( 8000 decimal ) and the bug still triggers.
Maybe it's related to the following logic in "vcs_size"? ( not sure about that.. )
221 if (use_attributes(inode)) { 222 if (use_unicode(inode)) 223 return -EOPNOTSUPP; 224 size = 2*size + HEADER_SIZE; 225 } else if (use_unicode(inode)) 226 size *= 4; 227 return size;
Why in the case of "use_unicode(inode)" size is multiplied by 4 and not 2? ( as we can see in line 224 )
On Mon, Nov 4, 2019 at 10:54 PM Jiri Slaby <jslaby@suse.com> wrote: > > On 04. 11. 19, 19:33, Nicolas Pitre wrote: > > On Mon, 4 Nov 2019, Or Cohen wrote: > > > >> @gregkh@linuxfoundation.org @nico@fluxnic.net - Thanks for the quick response. > >> @gregkh@linuxfoundation.org - Regarding your question, I don't think > >> the 1 byte buffer is related to the problem. ( it's just was there in > >> the initial reproducer the fuzzer created, and I forgot to remove it > >> while reducing code from the reproducer ). > > > > I think I know what the problem is. I have no time to test it though. > > > > Please try this (untested) patch. Also please try running the same test > > code but with vcsa6 in addition to vcsu6 to be sure. > > > > ---------- >8 > > Subject: [PATCH] vcs: add missing validation on vcs_size() returned value > > > > One usage instance didn't account for the fact that vcs_size() may > > return a negative error code. > > > > Signed-off-by: Nicolas Pitre <npitre@baylibre.com> > > > > diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c > > index 1f042346e7..fa07d79027 100644 > > --- a/drivers/tty/vt/vc_screen.c > > +++ b/drivers/tty/vt/vc_screen.c > > @@ -474,6 +474,10 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) > > goto unlock_out; > > > > size = vcs_size(inode); > > + if (size < 0) { > > + ret = size; > > + goto unlock_out; > > + } > > ret = -EINVAL; > > if (pos < 0 || pos > size) > > goto unlock_out; > > pos must be >= 0, so "pos > size" would catch this case as a side > effect, or am I missing something? That being said, the patch is > correct, but won't fix the issue IMO. > > thanks, > -- > js > suse labs
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