On Fri, Sep 23, 2022 at 01:28:09PM -0700, Kees Cook wrote:
Instead of discovering the kmalloc bucket size _after_ allocation, round up proactively so the allocation is explicitly made for the full size, allowing the compiler to correctly reason about the resulting size of the buffer through the existing __alloc_size() hint.
This will allow for kernels built with CONFIG_UBSAN_BOUNDS or the coming dynamic bounds checking under CONFIG_FORTIFY_SOURCE to gain back the __alloc_size() hints that were temporarily reverted in commit 93dd04ab0b2b ("slab: remove __alloc_size attribute from __kmalloc_track_caller")
Additionally tries to normalize size variables to u32 from int. Most interfaces are using "int", but notably __alloc_skb uses unsigned int.
Also fix some reverse Christmas tree and comments while touching nearby code.
Something in this patch is breaking things -- I've refactored it again to avoid overwriting the incoming size argument, and instead add a dedicated outgoing size variable. Here's what will be v3 ...
--- net/core/skbuff.c | 41 ++++++++++++++++++++++------------------- 1 file changed, 22 insertions(+), 19 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 974bbbbe7138..9b5a9fb69d9d 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -346,11 +346,12 @@ EXPORT_SYMBOL(napi_build_skb); * memory is free */ static void *kmalloc_reserve(size_t size, gfp_t flags, int node, - bool *pfmemalloc) + bool *pfmemalloc, size_t *alloc_size) { void *obj; bool ret_pfmemalloc = false;
+ size = kmalloc_size_roundup(size); /* * Try a regular allocation, when that fails and we're not entitled * to the reserves, fail. @@ -369,6 +370,7 @@ static void *kmalloc_reserve(size_t size, gfp_t flags, int node, if (pfmemalloc) *pfmemalloc = ret_pfmemalloc;
+ *alloc_size = size; return obj; }
@@ -400,7 +402,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, { struct kmem_cache *cache; struct sk_buff *skb; - unsigned int osize; + size_t alloc_size; bool pfmemalloc; u8 *data;
@@ -427,15 +429,15 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, */ size = SKB_DATA_ALIGN(size); size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); - data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc); - if (unlikely(!data)) - goto nodata; - /* kmalloc(size) might give us more room than requested. + /* kmalloc(size) might give us more room than requested, so + * allocate the true bucket size up front. * Put skb_shared_info exactly at the end of allocated zone, * to allow max possible filling before reallocation. */ - osize = ksize(data); - size = SKB_WITH_OVERHEAD(osize); + data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc, &alloc_size); + if (unlikely(!data)) + goto nodata; + size = SKB_WITH_OVERHEAD(alloc_size); prefetchw(data + size);
/* @@ -444,7 +446,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask, * the tail pointer in struct sk_buff! */ memset(skb, 0, offsetof(struct sk_buff, tail)); - __build_skb_around(skb, data, osize); + __build_skb_around(skb, data, alloc_size); skb->pfmemalloc = pfmemalloc;
if (flags & SKB_ALLOC_FCLONE) { @@ -1709,6 +1711,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, { int i, osize = skb_end_offset(skb); int size = osize + nhead + ntail; + size_t alloc_size; long off; u8 *data;
@@ -1723,10 +1726,10 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, if (skb_pfmemalloc(skb)) gfp_mask |= __GFP_MEMALLOC; data = kmalloc_reserve(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), - gfp_mask, NUMA_NO_NODE, NULL); + gfp_mask, NUMA_NO_NODE, NULL, &alloc_size); if (!data) goto nodata; - size = SKB_WITH_OVERHEAD(ksize(data)); + size = SKB_WITH_OVERHEAD(alloc_size);
/* Copy only real data... and, alas, header. This should be * optimized for the cases when header is void. @@ -6063,19 +6066,19 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off, int i; int size = skb_end_offset(skb); int new_hlen = headlen - off; + size_t alloc_size; u8 *data;
size = SKB_DATA_ALIGN(size);
if (skb_pfmemalloc(skb)) gfp_mask |= __GFP_MEMALLOC; - data = kmalloc_reserve(size + - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), - gfp_mask, NUMA_NO_NODE, NULL); + data = kmalloc_reserve(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), + gfp_mask, NUMA_NO_NODE, NULL, &alloc_size); if (!data) return -ENOMEM;
- size = SKB_WITH_OVERHEAD(ksize(data)); + size = SKB_WITH_OVERHEAD(alloc_size);
/* Copy real data, and all frags */ skb_copy_from_linear_data_offset(skb, off, data, new_hlen); @@ -6184,18 +6187,18 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, u8 *data; const int nfrags = skb_shinfo(skb)->nr_frags; struct skb_shared_info *shinfo; + size_t alloc_size;
size = SKB_DATA_ALIGN(size);
if (skb_pfmemalloc(skb)) gfp_mask |= __GFP_MEMALLOC; - data = kmalloc_reserve(size + - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), - gfp_mask, NUMA_NO_NODE, NULL); + data = kmalloc_reserve(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), + gfp_mask, NUMA_NO_NODE, NULL, &alloc_size); if (!data) return -ENOMEM;
- size = SKB_WITH_OVERHEAD(ksize(data)); + size = SKB_WITH_OVERHEAD(alloc_size);
memcpy((struct skb_shared_info *)(data + size), skb_shinfo(skb), offsetof(struct skb_shared_info, frags[0]));