pstore: Fix buffer overflow while write offset equal to buffer size

In case new offset is equal to prz->buffer_size, it won't wrap at this
time and will return old(overflow) value next time.

Signed-off-by: Liu ShuoX <shuox.liu@intel.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index de272d426763..ff7e3d4df5a1 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -54,7 +54,7 @@ static size_t buffer_start_add_atomic(struct persistent_ram_zone *prz, size_t a)
         do {
                 old = atomic_read(&prz->buffer->start);
                 new = old + a;
-                while (unlikely(new > prz->buffer_size))
+                while (unlikely(new >= prz->buffer_size))
                         new -= prz->buffer_size;
         } while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);
 
@@ -91,7 +91,7 @@ static size_t buffer_start_add_locked(struct persistent_ram_zone *prz, size_t a)
 
         old = atomic_read(&prz->buffer->start);
         new = old + a;
-        while (unlikely(new > prz->buffer_size))
+        while (unlikely(new >= prz->buffer_size))
                 new -= prz->buffer_size;
         atomic_set(&prz->buffer->start, new);