[iov_iter] fix iterate_all_kinds() on empty iterators

Problem similar to ones dealt with in "fold checks into iterate_and_advance()"
and followups, except that in this case we really want to do nothing when
asked for zero-length operation - unlike zero-length iterate_and_advance(),
zero-length iterate_all_kinds() has no side effects, and callers are simpler
that way.

That got exposed when copy_from_iter_full() had been used by tipc, which
builds an msghdr with zero payload and (now) feeds it to a primitive
based on iterate_all_kinds() instead of iterate_and_advance().

Reported-by: Jon Maloy <jon.maloy@ericsson.com>
Tested-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 26 insertions, 29 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 228892dabba6..25f572303801 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -73,19 +73,21 @@
 }
 
 #define iterate_all_kinds(i, n, v, I, B, K) {                   \
-        size_t skip = i->iov_offset;                            \
-        if (unlikely(i->type & ITER_BVEC)) {                    \
-                struct bio_vec v;                               \
-                struct bvec_iter __bi;                          \
-                iterate_bvec(i, n, v, __bi, skip, (B))          \
-        } else if (unlikely(i->type & ITER_KVEC)) {             \
-                const struct kvec *kvec;                        \
-                struct kvec v;                                  \
-                iterate_kvec(i, n, v, kvec, skip, (K))          \
-        } else {                                                \
-                const struct iovec *iov;                        \
-                struct iovec v;                                 \
-                iterate_iovec(i, n, v, iov, skip, (I))          \
+        if (likely(n)) {                                        \
+                size_t skip = i->iov_offset;                    \
+                if (unlikely(i->type & ITER_BVEC)) {            \
+                        struct bio_vec v;                       \
+                        struct bvec_iter __bi;                  \
+                        iterate_bvec(i, n, v, __bi, skip, (B))  \
+                } else if (unlikely(i->type & ITER_KVEC)) {     \
+                        const struct kvec *kvec;                \
+                        struct kvec v;                          \
+                        iterate_kvec(i, n, v, kvec, skip, (K))  \
+                } else {                                        \
+                        const struct iovec *iov;                \
+                        struct iovec v;                         \
+                        iterate_iovec(i, n, v, iov, skip, (I))  \
+                }                                               \
         }                                                       \
 }
 
@@ -576,7 +578,7 @@ bool copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i)
                 WARN_ON(1);
                 return false;
         }
-        if (unlikely(i->count < bytes))                         \
+        if (unlikely(i->count < bytes))
                 return false;
 
         iterate_all_kinds(i, bytes, v, ({
@@ -620,7 +622,7 @@ bool copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i)
                 WARN_ON(1);
                 return false;
         }
-        if (unlikely(i->count < bytes))                         \
+        if (unlikely(i->count < bytes))
                 return false;
         iterate_all_kinds(i, bytes, v, ({
                 if (__copy_from_user_nocache((to += v.iov_len) - v.iov_len,
@@ -837,11 +839,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
         unsigned long res = 0;
         size_t size = i->count;
 
-        if (!size)
-                return 0;
-
         if (unlikely(i->type & ITER_PIPE)) {
-                if (i->iov_offset && allocated(&i->pipe->bufs[i->idx]))
+                if (size && i->iov_offset && allocated(&i->pipe->bufs[i->idx]))
                         return size | i->iov_offset;
                 return size;
         }
@@ -856,10 +855,8 @@ EXPORT_SYMBOL(iov_iter_alignment);
 
 unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
 {
-        unsigned long res = 0;
+        unsigned long res = 0;
         size_t size = i->count;
-        if (!size)
-                return 0;
 
         if (unlikely(i->type & ITER_PIPE)) {
                 WARN_ON(1);
@@ -874,7 +871,7 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
                 (res |= (!res ? 0 : (unsigned long)v.iov_base) |
                         (size != v.iov_len ? size : 0))
                 );
-                return res;
+        return res;
 }
 EXPORT_SYMBOL(iov_iter_gap_alignment);
 
@@ -908,6 +905,9 @@ static ssize_t pipe_get_pages(struct iov_iter *i,
         size_t capacity;
         int idx;
 
+        if (!maxsize)
+                return 0;
+
         if (!sanity(i))
                 return -EFAULT;
 
@@ -926,9 +926,6 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
         if (maxsize > i->count)
                 maxsize = i->count;
 
-        if (!maxsize)
-                return 0;
-
         if (unlikely(i->type & ITER_PIPE))
                 return pipe_get_pages(i, pages, maxsize, maxpages, start);
         iterate_all_kinds(i, maxsize, v, ({
@@ -975,6 +972,9 @@ static ssize_t pipe_get_pages_alloc(struct iov_iter *i,
         int idx;
         int npages;
 
+        if (!maxsize)
+                return 0;
+
         if (!sanity(i))
                 return -EFAULT;
 
@@ -1006,9 +1006,6 @@ ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
         if (maxsize > i->count)
                 maxsize = i->count;
 
-        if (!maxsize)
-                return 0;
-
         if (unlikely(i->type & ITER_PIPE))
                 return pipe_get_pages_alloc(i, pages, maxsize, start);
         iterate_all_kinds(i, maxsize, v, ({