[PATCH] powerpc/spufs: Check file offset before calculating write size in fixed-sized files

[Jeremy Kerr <jk@ozlabs.org>]

Based on an original patch from Roel Kluin <roel.kluin@gmail.com>.

The write size calculated during regs and fpcr writes may currently
go negative. Because size is unsigned, this will wrap, and our
check for EFBIG will fail.

Instead, do the check for EFBIG before subtracting from size.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

---
Roel - How about this? clear up the logic a little rather than casting

---
 arch/powerpc/platforms/cell/spufs/file.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/platforms/cell/spufs/file.c b/arch/powerpc/platforms/cell/spufs/file.c
index 0da7f2b..83ef889 100644
--- a/arch/powerpc/platforms/cell/spufs/file.c
+++ b/arch/powerpc/platforms/cell/spufs/file.c
@@ -568,9 +568,10 @@ spufs_regs_write(struct file *file, const char __user *buffer,
 	struct spu_lscsa *lscsa = ctx->csa.lscsa;
 	int ret;
 
-	size = min_t(ssize_t, sizeof lscsa->gprs - *pos, size);
-	if (size <= 0)
+	if (*pos >= sizeof(lscsa->gprs))
 		return -EFBIG;
+
+	size = min_t(ssize_t, sizeof(lscsa->gprs) - *pos, size);
 	*pos += size;
 
 	ret = spu_acquire_saved(ctx);
@@ -623,10 +624,11 @@ spufs_fpcr_write(struct file *file, const char __user * buffer,
 	struct spu_lscsa *lscsa = ctx->csa.lscsa;
 	int ret;
 
-	size = min_t(ssize_t, sizeof(lscsa->fpcr) - *pos, size);
-	if (size <= 0)
+	if (*pos >= sizeof(lscsa->fpcr))
 		return -EFBIG;
 
+	size = min_t(ssize_t, sizeof(lscsa->fpcr) - *pos, size);
+
 	ret = spu_acquire_saved(ctx);
 	if (ret)
 		return ret;