From: Colin Ian King <[email protected]>
Currently extent and index i are both being incremented causing
an array out of bounds read on extent[i]. Fix this by removing
the extraneous increment of extent.
Detected by CoverityScan, CID#711541 ("Out of bounds read")
Fixes: d1081202f1d0 ("HFS rewrite")
Signed-off-by: Colin Ian King <[email protected]>
---
fs/hfs/extent.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
index 5d0182654580..636cdfcecb26 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -300,7 +300,7 @@ int hfs_free_fork(struct super_block *sb, struct hfs_cat_file *file, int type)
return 0;
blocks = 0;
- for (i = 0; i < 3; extent++, i++)
+ for (i = 0; i < 3; i++)
blocks += be16_to_cpu(extent[i].count);
res = hfs_free_extents(sb, extent, blocks, blocks);
--
2.17.1
On Fri, Aug 31, 2018 at 03:05:38PM +0100, Colin King wrote:
> From: Colin Ian King <[email protected]>
>
> Currently extent and index i are both being incremented causing
> an array out of bounds read on extent[i]. Fix this by removing
> the extraneous increment of extent.
>
> Detected by CoverityScan, CID#711541 ("Out of bounds read")
>
> Fixes: d1081202f1d0 ("HFS rewrite")
> Signed-off-by: Colin Ian King <[email protected]>
I don't think this got picked up yet; let's see if I can help.
Reviewed-by: Ernesto A. Fernández <[email protected]>
> ---
> fs/hfs/extent.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
> index 5d0182654580..636cdfcecb26 100644
> --- a/fs/hfs/extent.c
> +++ b/fs/hfs/extent.c
> @@ -300,7 +300,7 @@ int hfs_free_fork(struct super_block *sb, struct hfs_cat_file *file, int type)
> return 0;
>
> blocks = 0;
> - for (i = 0; i < 3; extent++, i++)
> + for (i = 0; i < 3; i++)
> blocks += be16_to_cpu(extent[i].count);
>
> res = hfs_free_extents(sb, extent, blocks, blocks);
> --
> 2.17.1
>
On Wed, Oct 17, 2018 at 03:01:17PM -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2018 15:05:38 +0100 Colin King <[email protected]> wrote:
>
> > From: Colin Ian King <[email protected]>
> >
> > Currently extent and index i are both being incremented causing
> > an array out of bounds read on extent[i]. Fix this by removing
> > the extraneous increment of extent.
> >
> > Detected by CoverityScan, CID#711541 ("Out of bounds read")
> >
> > Fixes: d1081202f1d0 ("HFS rewrite")
>
> No such commit here. I assume this is 7cb74be6fd827e314f8.
>
> > --- a/fs/hfs/extent.c
> > +++ b/fs/hfs/extent.c
> > @@ -300,7 +300,7 @@ int hfs_free_fork(struct super_block *sb, struct hfs_cat_file *file, int type)
> > return 0;
> >
> > blocks = 0;
> > - for (i = 0; i < 3; extent++, i++)
> > + for (i = 0; i < 3; i++)
> > blocks += be16_to_cpu(extent[i].count);
> >
> > res = hfs_free_extents(sb, extent, blocks, blocks);
>
> Well, that's quite the bug. Question is, why didn't anyone notice it.
> What are the runtime effects? A disk space leak, perhaps?
>
> I worry a bit that, given the fs was evidently working "ok", perhaps
> this error was corrected elsewhere in the code and that "fixing" this
> site will have unexpected and undesirable runtime effects. Can someone
> help me out here?
hfs_free_extents() seems to expect the 'offset' argument to be the
sum of ->count of 1--3 starting elements of extent array. In case of
mismatch, it returns -EIO and that's it - hfs_free_fork() will bugger
off with -EIO at that point. If it does match, block_nr is supposed
to be in range 0..offset and blocks offset - block_nr .. offset - 1
are freed.
So at a guess, that sucker mostly ends up leaking blocks. Said that,
it means that the rest of hfs_free_fork() has never been tested.
I'd suggest somebody to turn that
/* panic? */
return -EIO;
in hfs_free_extents() into
printk(KERN_ERR "hfs_free_extents is fucked");
return -EIO;
and see if it's triggerable. Then check if there's a block leak in
the reproducer, whatever it is.
On Wed, 2018-10-17 at 15:01 -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2018 15:05:38 +0100 Colin King <[email protected]> wrote:
>
> > From: Colin Ian King <[email protected]>
> >
> > Currently extent and index i are both being incremented causing
> > an array out of bounds read on extent[i]. Fix this by removing
> > the extraneous increment of extent.
> >
> > Detected by CoverityScan, CID#711541 ("Out of bounds read")
> >
> > Fixes: d1081202f1d0 ("HFS rewrite")
>
> No such commit here. I assume this is 7cb74be6fd827e314f8.
>
> > --- a/fs/hfs/extent.c
> > +++ b/fs/hfs/extent.c
> > @@ -300,7 +300,7 @@ int hfs_free_fork(struct super_block *sb, struct hfs_cat_file *file, int type)
> > return 0;
> >
> > blocks = 0;
> > - for (i = 0; i < 3; extent++, i++)
By the way, the hfs_free_extents() has the same logic [1] of for (i = 0;
i < 3; extent++, i++). It looks like that the bug is not fixed yet. Did
anyone test this patch? What's the real reproduction path for the bug?
Thanks,
Vyacheslav Dubeyko.
[1] https://elixir.bootlin.com/linux/latest/source/fs/hfs/extent.c#L251
> > + for (i = 0; i < 3; i++)
> > blocks += be16_to_cpu(extent[i].count);
> >
> > res = hfs_free_extents(sb, extent, blocks, blocks);
>
> Well, that's quite the bug. Question is, why didn't anyone notice it.
> What are the runtime effects? A disk space leak, perhaps?
>
> I worry a bit that, given the fs was evidently working "ok", perhaps
> this error was corrected elsewhere in the code and that "fixing" this
> site will have unexpected and undesirable runtime effects. Can someone
> help me out here?
On Wed, Oct 17, 2018 at 03:01:17PM -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2018 15:05:38 +0100 Colin King <[email protected]> wrote:
>
> > From: Colin Ian King <[email protected]>
> >
> > Currently extent and index i are both being incremented causing
> > an array out of bounds read on extent[i]. Fix this by removing
> > the extraneous increment of extent.
> >
> > Detected by CoverityScan, CID#711541 ("Out of bounds read")
> >
> > Fixes: d1081202f1d0 ("HFS rewrite")
>
> No such commit here. I assume this is 7cb74be6fd827e314f8.
Sorry, I missed that. This bug has actually been here since before the
first git commit.
>
> > --- a/fs/hfs/extent.c
> > +++ b/fs/hfs/extent.c
> > @@ -300,7 +300,7 @@ int hfs_free_fork(struct super_block *sb, struct hfs_cat_file *file, int type)
> > return 0;
> >
> > blocks = 0;
> > - for (i = 0; i < 3; extent++, i++)
> > + for (i = 0; i < 3; i++)
> > blocks += be16_to_cpu(extent[i].count);
> >
> > res = hfs_free_extents(sb, extent, blocks, blocks);
>
> Well, that's quite the bug. Question is, why didn't anyone notice it.
> What are the runtime effects?
This is only triggered when deleting a file with a resource fork. I may
be wrong because the documentation isn't clear, but I don't think you can
create those under linux. So I guess nobody was testing them.
> A disk space leak, perhaps?
That's what it looks like in general. hfs_free_extents() won't do anything
if the block count doesn't add up, and the error will be ignored. Now, if
the block count randomly does add up, we could see some corruption.
> I worry a bit that, given the fs was evidently working "ok", perhaps
> this error was corrected elsewhere in the code and that "fixing" this
> site will have unexpected and undesirable runtime effects. Can someone
> help me out here?
I don't think so. This bug also makes extent point to the wrong place on
the following call to hfs_free_extents(). There is no way this can work
correctly in general.