[PATCH] xfs_repair: don't let bplist index go negative in prefetch

[Eric Sandeen]

After:

bbd3275 repair: don't unlock prefetch tree to read discontig buffers

Coverity spotted that it's possible for us to arrive at the loop
below with num == 1, and then we decrement it to 0, and try to
index bplist[num-1].

I think this was possible before the change, i.e. it's probably
not a regression.

Fix this by not trying to shrink the window unless we have
more than one buffer in the array.

Signed-off-by: Eric Sandeen <sandeen at redhat.com>
---


diff --git a/repair/prefetch.c b/repair/prefetch.c
index 4595310..b6d4755 100644
--- a/repair/prefetch.c
+++ b/repair/prefetch.c
@@ -505,7 +505,7 @@ pf_batch_read(
 		first_off = LIBXFS_BBTOOFF64(XFS_BUF_ADDR(bplist[0]));
 		last_off = LIBXFS_BBTOOFF64(XFS_BUF_ADDR(bplist[num-1])) +
 			XFS_BUF_SIZE(bplist[num-1]);
-		while (last_off - first_off > pf_max_bytes) {
+		while (num > 1 && last_off - first_off > pf_max_bytes) {
 			num--;
 			last_off = LIBXFS_BBTOOFF64(XFS_BUF_ADDR(bplist[num-1])) +
 				XFS_BUF_SIZE(bplist[num-1]);