[ 38/95] target: fix NULL pointer dereference bug alloc_page() fails to getmemory

[Ben Hutchings]

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yi Zou <yi.zou@xxxxxxxxx>

commit d0e27c88d795fb9647153063ec48051fd84e1731 upstream.

I am hitting this bug when the target is low in memory that fails the
alloc_page() for the newly submitted command. This is a sort of off-by-one
bug causing NULL pointer dereference in __free_page() since 'i' here is
really the counter of total pages that have been successfully allocated here.

Signed-off-by: Yi Zou <yi.zou@xxxxxxxxx>
Cc: Andy Grover <agrover@xxxxxxxxxx>
Cc: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Cc: Open-FCoE.org <devel@xxxxxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/target/target_core_transport.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 0eaae23..a7589cc 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -2294,9 +2294,9 @@ transport_generic_get_mem(struct se_cmd *cmd)
 	return 0;
 
 out:
-	while (i >= 0) {
-		__free_page(sg_page(&cmd->t_data_sg[i]));
+	while (i > 0) {
 		i--;
+		__free_page(sg_page(&cmd->t_data_sg[i]));
 	}
 	kfree(cmd->t_data_sg);
 	cmd->t_data_sg = NULL;


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