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Subject[PATCH] writev failures for iovec with invalid addresses.
Hi,
I debugged writev01 from the LTP testsuite and I found why it fails.
The third test in writev01 passes a 3 element iovec to sys_writev.
The first iovec is valid, the second points to an invalid address and
the third is valid again. As I read the specification writev should
write the first iovec and return the number of bytes in it. 2.5.69
returns -EFAULT. The reason is that filemap_copy_from_user_iovec
returns != 0 if ANY of the iovec elements is invalid. This causes
generic_file_aio_write_nolock not to write the valid elements in the
iovec. The return value will then be either too small or -EFAULT
instead of the real number of bytes that could have been written.
The attached patch should fix the problem. It changes filemap.c
to make filemap_copy_from_user/filemap_copy_from_user_iovec return
the number of successfully copied bytes instead of "page_fault".
generic_file_aio_write_nolock commits the write operation if at
least the first iovec has been valid and returns the correct number
of bytes. Comments ?

blue skies,
Martin.
----

Fix sys_writev for vectors which contain a invalid address in the middle
of the iovec list.

diffstat:
mm/filemap.c | 45 +++++++++++++++++++++++++--------------------
1 files changed, 25 insertions(+), 20 deletions(-)

diff -urN linux-2.5.69/mm/filemap.c linux-2.5.69-s390/mm/filemap.c
--- linux-2.5.69/mm/filemap.c Thu May 22 13:26:29 2003
+++ linux-2.5.69-s390/mm/filemap.c Thu May 22 13:26:47 2003
@@ -1410,7 +1410,7 @@
}
}

-static inline int
+static inline size_t
filemap_copy_from_user(struct page *page, unsigned long offset,
const char __user *buf, unsigned bytes)
{
@@ -1427,44 +1427,45 @@
left = __copy_from_user(kaddr + offset, buf, bytes);
kunmap(page);
}
- return left;
+ return left ? 0 : bytes;
}

-static int
+static size_t
__filemap_copy_from_user_iovec(char *vaddr,
const struct iovec *iov, size_t base, size_t bytes)
{
- int left = 0;
+ size_t copied = 0;

while (bytes) {
char __user *buf = iov->iov_base + base;
int copy = min(bytes, iov->iov_len - base);
base = 0;
- if ((left = __copy_from_user(vaddr, buf, copy)))
+ if (__copy_from_user(vaddr, buf, copy))
break;
+ copied += copy;
bytes -= copy;
vaddr += copy;
iov++;
}
- return left;
+ return copied;
}

-static inline int
+static inline size_t
filemap_copy_from_user_iovec(struct page *page, unsigned long offset,
const struct iovec *iov, size_t base, size_t bytes)
{
char *kaddr;
- int left;
+ size_t copied;

kaddr = kmap_atomic(page, KM_USER0);
- left = __filemap_copy_from_user_iovec(kaddr + offset, iov, base, bytes);
+ copied = __filemap_copy_from_user_iovec(kaddr + offset, iov, base, bytes);
kunmap_atomic(kaddr, KM_USER0);
- if (left != 0) {
+ if (copied != bytes) {
kaddr = kmap(page);
- left = __filemap_copy_from_user_iovec(kaddr + offset, iov, base, bytes);
+ copied = __filemap_copy_from_user_iovec(kaddr + offset, iov, base, bytes);
kunmap(page);
}
- return left;
+ return copied;
}

static inline void
@@ -1672,7 +1673,7 @@
do {
unsigned long index;
unsigned long offset;
- long page_fault;
+ size_t copied;

offset = (pos & (PAGE_CACHE_SIZE -1)); /* Within page */
index = pos >> PAGE_CACHE_SHIFT;
@@ -1707,18 +1708,18 @@
break;
}
if (likely(nr_segs == 1))
- page_fault = filemap_copy_from_user(page, offset,
+ copied = filemap_copy_from_user(page, offset,
buf, bytes);
else
- page_fault = filemap_copy_from_user_iovec(page, offset,
+ copied = filemap_copy_from_user_iovec(page, offset,
cur_iov, iov_base, bytes);
flush_dcache_page(page);
- status = a_ops->commit_write(file, page, offset, offset+bytes);
- if (unlikely(page_fault)) {
- status = -EFAULT;
- } else {
+ if (likely(copied > 0)) {
+ status = a_ops->commit_write(file, page, offset,
+ offset + copied);
+
if (!status)
- status = bytes;
+ status = copied;

if (status >= 0) {
written += status;
@@ -1730,6 +1731,10 @@
&iov_base, status);
}
}
+ if (unlikely(copied != bytes))
+ if (status >= 0)
+ status = -EFAULT;
+
if (!PageReferenced(page))
SetPageReferenced(page);
unlock_page(page);
-
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