[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>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 228892dabba6f5579478988b84ef007fa04bd661..25f57230380104f419257ea43c1cd3d2e31d7e65 100644 (file)
--- 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, ({