zap_modalias_env() wrongly calculates size of memory block to move, so
will cause OOB memory access issue if variable MODALIAS is not the last
one within its @env parameter, fixed by correcting size to memmove.
Fixes: 9b3fa47d4a76 ("kobject: fix suppressing modalias in uevents delivered over netlink")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zijun Hu <quic_zijuhu@xxxxxxxxxxx>
---
V1 -> V2: Correct commit messages and add inline comments
V1 discussion link:
https://lore.kernel.org/lkml/0b916393-eb39-4467-9c99-ac1bc9746512@xxxxxxxxxxx/T/#m8d80165294640dbac72f5c48d14b7ca4f097b5c7
lib/kobject_uevent.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 03b427e2707e..f22366be020c 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -433,8 +433,23 @@ static void zap_modalias_env(struct kobj_uevent_env *env)
len = strlen(env->envp[i]) + 1;
if (i != env->envp_idx - 1) {
+ /* @env->envp[] contains pointers to @env->buf[]
+ * with @env->buflen elements, and we want to
+ * remove variable MODALIAS pointed by
+ * @env->envp[i] with length @len as shown below:
+ *
+ * 0 @env->buf[] @env->buflen
+ * ----------------------------------------
+ * ^ ^ ^
+ * |-> @len <-| target block |
+ * @env->envp[i] @env->envp[i+1]
+ *
+ * so the "target block" indicated above is moved
+ * backward by @len, and its right size is
+ * (@env->buf + @env->buflen - @env->envp[i + 1]).
+ */
memmove(env->envp[i], env->envp[i + 1],
- env->buflen - len);
+ env->buf + env->buflen - env->envp[i + 1]);
for (j = i; j < env->envp_idx - 1; j++)
env->envp[j] = env->envp[j + 1] - len;
--
2.7.4
