[PATCH 02/10] module: fix out-of-range memory access

[Tejun Heo]

Impact: subtle memory access bug fix

percpu_modalloc() may access pcpu_size[-1].  The access won't change
the value by itself but it still is read/write access and dangerous.
Fix it.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/module.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index ba22484..d54a63e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -426,12 +426,14 @@ static void *percpu_modalloc(unsigned long size, unsigned long align,
 			continue;
 
 		/* Transfer extra to previous block. */
-		if (pcpu_size[i-1] < 0)
-			pcpu_size[i-1] -= extra;
-		else
-			pcpu_size[i-1] += extra;
-		pcpu_size[i] -= extra;
-		ptr += extra;
+		if (extra) {
+			if (pcpu_size[i-1] < 0)
+				pcpu_size[i-1] -= extra;
+			else
+				pcpu_size[i-1] += extra;
+			pcpu_size[i] -= extra;
+			ptr += extra;
+		}
 
 		/* Split block if warranted */
 		if (pcpu_size[i] - size > sizeof(unsigned long))
-- 
1.6.0.2

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