[ndctl PATCH] ndctl: Work around kernel memory corruption

[Keith Busch <keith.busch@intel.com>]

Kernel commit efda1b5d87cb ("acpi, nfit, libnvdimm: fix / harden
ars_status output length handling") contained an incorrect ars status
output size calculation and may overrun the buffer provided by 4
bytes. This patch adds 4 bytes to the buffer the user space allocates
so that the kernel's overrun doesn't corrupt the application's heap.

See kernel patch for more details:

  https://patchwork.kernel.org/patch/10563103/

Signed-off-by: Keith Busch <keith.busch@intel.com>
---
 ndctl/lib/ars.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/ndctl/lib/ars.c b/ndctl/lib/ars.c
index c78e3bf..bd75131 100644
--- a/ndctl/lib/ars.c
+++ b/ndctl/lib/ars.c
@@ -133,7 +133,16 @@ NDCTL_EXPORT struct ndctl_cmd *ndctl_bus_cmd_new_ars_status(struct ndctl_cmd *ar
 	}
 
 	size = sizeof(*cmd) + ars_cap_cmd->max_ars_out;
-	cmd = calloc(1, size);
+
+	/*
+	 * Older kernels have a bug that miscalculates the output length of the
+	 * ars status and will overrun the provided buffer by 4 bytes,
+	 * corrupting the memory. Add an additional 4 bytes in the allocation
+	 * size to prevent that corruption. See kernel patch for more details:
+	 *
+	 *   https://patchwork.kernel.org/patch/10563103/
+	 */
+	cmd = calloc(1, size + 4);
 	if (!cmd)
 		return NULL;
 
-- 
2.14.4

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