On Tue, 21 Jan 2014 17:00:00 +0530 Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> wrote: > We could hit null pointer dereference error during alloc_page_buffers > in : (1) block size > PAGE_SIZE (2) low memory. > Add sanity check for that. > > Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> > --- > fs/block_dev.c | 1 + > fs/buffer.c | 6 ++++++ > 2 files changed, 7 insertions(+) > > diff --git a/fs/block_dev.c b/fs/block_dev.c > index 1e86823..2481d42 100644 > --- a/fs/block_dev.c > +++ b/fs/block_dev.c > @@ -1027,6 +1027,7 @@ void bd_set_size(struct block_device *bdev, loff_t size) > break; > bsize <<= 1; > } > + BUG_ON(bsize > PAGE_SIZE); > bdev->bd_block_size = bsize; > bdev->bd_inode->i_blkbits = blksize_bits(bsize); > } alloc_page_buffers() will always return NULL if passed size >= PAGE_SIZE. So if we're going to add a check, it would be better to add it to alloc_page_buffers() because that will catch errors from the widest range of callsites. But alloc_page_buffers() is pretty frequently called and I'd be inclined to not add any check - most callers will just go oops and that will provide basically the same information. > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1571,6 +1571,12 @@ void create_empty_buffers(struct page *page, > struct buffer_head *bh, *head, *tail; > > head = alloc_page_buffers(page, blocksize, 1); > + > + /* > + * alloc_page_buffers() could return NULL on (1) bs > PAGE_SIZE > + * (2) low memory case. Ensure that we don't dereference null ptr > + */ > + BUG_ON(!head); This is unneeded. - bs > PAGE_SIZE can be checked elsewhere in a direct fashion - low memory case can't happen - we passed retry=1 - create_empty_buffers() will immediately go oops if head==NULL. That oops contains the same info as is presented by a BUG(). -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
