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>

diff --git a/fs/compat.c b/fs/compat.c
index 52cfeb61da77c14ce7d3838db7517b5b6f88b213..ff66c0d7583d51eb672587a9c685cbc91320b167 100644 (file)
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -606,14 +606,14 @@ ssize_t compat_rw_copy_check_uvector(int type,
        /*
         * Single unix specification:
         * We should -EINVAL if an element length is not >= 0 and fitting an
-        * ssize_t.  The total length is fitting an ssize_t
+        * ssize_t.
         *
-        * Be careful here because iov_len is a size_t not an ssize_t
+        * In Linux, the total length is limited to MAX_RW_COUNT, there is
+        * no overflow possibility.
         */
        tot_len = 0;
        ret = -EINVAL;
        for (seg = 0; seg < nr_segs; seg++) {
-               compat_ssize_t tmp = tot_len;
                compat_uptr_t buf;
                compat_ssize_t len;
 
@@ -624,13 +624,13 @@ ssize_t compat_rw_copy_check_uvector(int type,
                }
                if (len < 0)    /* size_t not fitting in compat_ssize_t .. */
                        goto out;
-               tot_len += len;
-               if (tot_len < tmp) /* maths overflow on the compat_ssize_t */
-                       goto out;
                if (!access_ok(vrfy_dir(type), compat_ptr(buf), len)) {
                        ret = -EFAULT;
                        goto out;
                }
+               if (len > MAX_RW_COUNT - tot_len)
+                       len = MAX_RW_COUNT - tot_len;
+               tot_len += len;
                iov->iov_base = compat_ptr(buf);
                iov->iov_len = (compat_size_t) len;
                uvector++;

diff --git a/fs/read_write.c b/fs/read_write.c
index 9cd9d148105d287b55c9f60af4034f300cc6d1af..431a0ed610c83a8750592e516ff23ac35ffbe524 100644 (file)
--- 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;

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4d07902bc50c0e11dff997ffa16c4aa6e449c214..7b7b507ffa1cb269266e74044e8e57ec8e0b5d7b 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1867,6 +1867,7 @@ extern int current_umask(void);
 /* /sys/fs */
 extern struct kobject *fs_kobj;
 
+#define MAX_RW_COUNT (INT_MAX & PAGE_CACHE_MASK)
 extern int rw_verify_area(int, struct file *, loff_t *, size_t);
 
 #define FLOCK_VERIFY_READ  1