On Mon, Jan 31, 2022 at 10:49:12PM -0500, Douglas Gilbert wrote: > This patch fixes a check done by sgl_alloc_order() before it starts > any allocations. The comment in the original said: "Check for integer > overflow" but the right hand side of the expression in the condition > is resolved as u32 so it can not exceed UINT32_MAX (4 GiB) which > means 'length' can not exceed that value. > > This function may be used to replace vmalloc(unsigned long) for a > large allocation (e.g. a ramdisk). vmalloc has no limit at 4 GiB so > it seems unreasonable that sgl_alloc_order() whose length type is > unsigned long long should be limited to 4 GB. > > In early 2021 there was discussion between Jason Gunthorpe > <jgg@xxxxxxxx> and Bodo Stroesser <bostroesser@xxxxxxxxx> about the > way to check for overflow caused by order (an exponent) being > too large. Take the solution proposed by Bodo in post dated > 20210118 to the linux-scsi and linux-block lists. > > An earlier patch fixed a memory leak in sg_alloc_order() due to the > misuse of sgl_free(). Take the opportunity to put a one line comment > above sgl_free()'s declaration warning that it is not suitable when > order > 0 . > > Cc: Jason Gunthorpe <jgg@xxxxxxxx> > Reviewed-by: Bodo Stroesser <bostroesser@xxxxxxxxx> > Signed-off-by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx> > --- > include/linux/scatterlist.h | 1 + > lib/scatterlist.c | 24 +++++++++++++----------- > 2 files changed, 14 insertions(+), 11 deletions(-) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 7ff9d6386c12..03130be581bb 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -357,6 +357,7 @@ struct scatterlist *sgl_alloc(unsigned long long length, gfp_t gfp, > unsigned int *nent_p); > void sgl_free_n_order(struct scatterlist *sgl, int nents, int order); > void sgl_free_order(struct scatterlist *sgl, int order); > +/* Only use sgl_free() when order is 0 */ > void sgl_free(struct scatterlist *sgl); > #endif /* CONFIG_SGL_ALLOC */ > > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > index d5e82e4a57ad..ed6d0465c78e 100644 > --- a/lib/scatterlist.c > +++ b/lib/scatterlist.c > @@ -585,13 +585,16 @@ EXPORT_SYMBOL(sg_alloc_table_from_pages_segment); > #ifdef CONFIG_SGL_ALLOC > > /** > - * sgl_alloc_order - allocate a scatterlist and its pages > + * sgl_alloc_order - allocate a scatterlist with equally sized elements each > + * of which has 2^@order continuous pages > * @length: Length in bytes of the scatterlist. Must be at least one > - * @order: Second argument for alloc_pages() > + * @order: Second argument for alloc_pages(). Each sgl element size will > + * be (PAGE_SIZE*2^@order) bytes. @order must not exceed 16. > * @chainable: Whether or not to allocate an extra element in the scatterlist > - * for scatterlist chaining purposes > + * for scatterlist chaining purposes > * @gfp: Memory allocation flags > - * @nent_p: [out] Number of entries in the scatterlist that have pages > + * @nent_p: [out] Number of entries in the scatterlist that have pages. > + * Ignored if @nent_p is NULL. > * > * Returns: A pointer to an initialized scatterlist or %NULL upon failure. > */ > @@ -604,16 +607,15 @@ struct scatterlist *sgl_alloc_order(unsigned long long length, > unsigned int nent, nalloc; > u32 elem_len; > > - nent = round_up(length, PAGE_SIZE << order) >> (PAGE_SHIFT + order); > - /* Check for integer overflow */ > - if (length > (nent << (PAGE_SHIFT + order))) > + if (length >> (PAGE_SHIFT + order) >= UINT_MAX) > return NULL; > - nalloc = nent; > + nent = DIV_ROUND_UP(length, PAGE_SIZE << order); > + This would be clearer to make nent/etc an unsigned long long. Then check if nalloc is > SIZE_MAX before casting it to size_t for the allocation. Avoids the wonky if statement. Kaspm
