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authorLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-01 13:17:28 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-01 13:17:28 -0700
commit75723957673bfa10c98b735259f891cc79cf0450 (patch)
tree7382ea8e4bbda6ddf8d6f29f708aa531e262cd36
parente2cd68f7cd07cc898581bd736ebdd6f2c2323c2e (diff)
Fix possible splice() mmap_sem deadlock
Nick Piggin points out that splice isn't being good about the mmap semaphore: while two readers can nest inside each others, it does leave a possible deadlock if a writer (ie a new mmap()) comes in during that nesting. Original "just move the locking" patch by Nick, replaced by one by me based on an optimistic pagefault_disable(). And then Jens tested and updated that patch. Reported-by: Nick Piggin <npiggin@suse.de> Tested-by: Jens Axboe <jens.axboe@oracle.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/splice.c46
1 files changed, 34 insertions, 12 deletions
diff --git a/fs/splice.c b/fs/splice.c
index c010a72ca2d2..e95a36228863 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1224,6 +1224,33 @@ static long do_splice(struct file *in, loff_t __user *off_in,
}
/*
+ * Do a copy-from-user while holding the mmap_semaphore for reading, in a
+ * manner safe from deadlocking with simultaneous mmap() (grabbing mmap_sem
+ * for writing) and page faulting on the user memory pointed to by src.
+ * This assumes that we will very rarely hit the partial != 0 path, or this
+ * will not be a win.
+ */
+static int copy_from_user_mmap_sem(void *dst, const void __user *src, size_t n)
+{
+ int partial;
+
+ pagefault_disable();
+ partial = __copy_from_user_inatomic(dst, src, n);
+ pagefault_enable();
+
+ /*
+ * Didn't copy everything, drop the mmap_sem and do a faulting copy
+ */
+ if (unlikely(partial)) {
+ up_read(&current->mm->mmap_sem);
+ partial = copy_from_user(dst, src, n);
+ down_read(&current->mm->mmap_sem);
+ }
+
+ return partial;
+}
+
+/*
* Map an iov into an array of pages and offset/length tupples. With the
* partial_page structure, we can map several non-contiguous ranges into
* our ones pages[] map instead of splitting that operation into pieces.
@@ -1236,31 +1263,26 @@ static int get_iovec_page_array(const struct iovec __user *iov,
{
int buffers = 0, error = 0;
- /*
- * It's ok to take the mmap_sem for reading, even
- * across a "get_user()".
- */
down_read(&current->mm->mmap_sem);
while (nr_vecs) {
unsigned long off, npages;
+ struct iovec entry;
void __user *base;
size_t len;
int i;
- /*
- * Get user address base and length for this iovec.
- */
- error = get_user(base, &iov->iov_base);
- if (unlikely(error))
- break;
- error = get_user(len, &iov->iov_len);
- if (unlikely(error))
+ error = -EFAULT;
+ if (copy_from_user_mmap_sem(&entry, iov, sizeof(entry)))
break;
+ base = entry.iov_base;
+ len = entry.iov_len;
+
/*
* Sanity check this iovec. 0 read succeeds.
*/
+ error = 0;
if (unlikely(!len))
break;
error = -EFAULT;