readv/writev: do the same MAX_RW_COUNT truncation that read/write does

We used to protect against overflow, but rather than return an error, do
what read/write does, namely to limit the total size to MAX_RW_COUNT.
This is not only more consistent, but it also means that any broken
low-level read/write routine that still keeps counts in 'int' can't
break.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 33 insertions, 29 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index 9cd9d148105d..431a0ed610c8 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -243,8 +243,6 @@ bad:
  * them to something that fits in "int" so that others
  * won't have to do range checks all the time.
  */
-#define MAX_RW_COUNT (INT_MAX & PAGE_CACHE_MASK)
-
 int rw_verify_area(int read_write, struct file *file, loff_t *ppos, size_t count)
 {
         struct inode *inode;
@@ -584,65 +582,71 @@ ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
                               unsigned long nr_segs, unsigned long fast_segs,
                               struct iovec *fast_pointer,
                               struct iovec **ret_pointer)
-  {
+{
         unsigned long seg;
-        ssize_t ret;
+        ssize_t ret;
         struct iovec *iov = fast_pointer;
 
-        /*
-         * SuS says "The readv() function *may* fail if the iovcnt argument
-         * was less than or equal to 0, or greater than {IOV_MAX}.  Linux has
-         * traditionally returned zero for zero segments, so...
-         */
+        /*
+         * SuS says "The readv() function *may* fail if the iovcnt argument
+         * was less than or equal to 0, or greater than {IOV_MAX}.  Linux has
+         * traditionally returned zero for zero segments, so...
+         */
         if (nr_segs == 0) {
                 ret = 0;
-                goto out;
+                goto out;
         }
 
-        /*
-         * First get the "struct iovec" from user memory and
-         * verify all the pointers
-         */
+        /*
+         * First get the "struct iovec" from user memory and
+         * verify all the pointers
+         */
         if (nr_segs > UIO_MAXIOV) {
                 ret = -EINVAL;
-                goto out;
+                goto out;
         }
         if (nr_segs > fast_segs) {
-                iov = kmalloc(nr_segs*sizeof(struct iovec), GFP_KERNEL);
+                iov = kmalloc(nr_segs*sizeof(struct iovec), GFP_KERNEL);
                 if (iov == NULL) {
                         ret = -ENOMEM;
-                        goto out;
+                        goto out;
                 }
-        }
+        }
         if (copy_from_user(iov, uvector, nr_segs*sizeof(*uvector))) {
                 ret = -EFAULT;
-                goto out;
+                goto out;
         }
 
-        /*
+        /*
          * According to the Single Unix Specification we should return EINVAL
          * if an element length is < 0 when cast to ssize_t or if the
          * total length would overflow the ssize_t return value of the
          * system call.
-         */
+         *
+         * Linux caps all read/write calls to MAX_RW_COUNT, and avoids the
+         * overflow case.
+         */
         ret = 0;
-        for (seg = 0; seg < nr_segs; seg++) {
-                void __user *buf = iov[seg].iov_base;
-                ssize_t len = (ssize_t)iov[seg].iov_len;
+        for (seg = 0; seg < nr_segs; seg++) {
+                void __user *buf = iov[seg].iov_base;
+                ssize_t len = (ssize_t)iov[seg].iov_len;
 
                 /* see if we we're about to use an invalid len or if
                  * it's about to overflow ssize_t */
-                if (len < 0 || (ret + len < ret)) {
+                if (len < 0) {
                         ret = -EINVAL;
-                        goto out;
+                        goto out;
                 }
                 if (unlikely(!access_ok(vrfy_dir(type), buf, len))) {
                         ret = -EFAULT;
-                        goto out;
+                        goto out;
+                }
+                if (len > MAX_RW_COUNT - ret) {
+                        len = MAX_RW_COUNT - ret;
+                        iov[seg].iov_len = len;
                 }
-
                 ret += len;
-        }
+        }
 out:
         *ret_pointer = iov;
         return ret;