2024-05-30 13:15:03

by Zijun Hu

Subject: [PATCH v3] kobject_uevent: Fix OOB access within zap_modalias_env()

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: [email protected]
Signed-off-by: Zijun Hu <[email protected]>
---
V3: Correct inline comments and take Dmitry's suggestion
V2: Correct commit messages and add inline comments

Previous discussion links:
https://lore.kernel.org/lkml/[email protected]/
https://lore.kernel.org/lkml/[email protected]/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..b7f2fa08d9c8 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 chars, and we are removing
+ * variable MODALIAS here pointed by @env->envp[i]
+ * with length @len as shown below:
+ *
+ * 0 @env->buf[] @env->buflen
+ * ---------------------------------------------
+ * ^ ^ ^ ^
+ * | |-> @len <-| target block |
+ * @env->envp[0] @env->envp[i] @env->envp[i + 1]
+ *
+ * so the "target block" indicated above is moved
+ * backward by @len, and its right size is
+ * @env->buflen - (@env->envp[i + 1] - @env->envp[0]).
+ */
memmove(env->envp[i], env->envp[i + 1],
- env->buflen - len);
+ env->buflen - (env->envp[i + 1] - env->envp[0]));

for (j = i; j < env->envp_idx - 1; j++)
env->envp[j] = env->envp[j + 1] - len;
--
2.7.4

2024-06-10 14:57:15

by Lk Sii

Subject: Re: [PATCH v3] kobject_uevent: Fix OOB access within zap_modalias_env()

On 2024/5/30 21:14, Zijun Hu wrote:
> 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: [email protected]
> Signed-off-by: Zijun Hu <[email protected]>
> ---
> V3: Correct inline comments and take Dmitry's suggestion
> V2: Correct commit messages and add inline comments
>
> Previous discussion links:
> https://lore.kernel.org/lkml/[email protected]/
> https://lore.kernel.org/lkml/[email protected]/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..b7f2fa08d9c8 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 chars, and we are removing
> + * variable MODALIAS here pointed by @env->envp[i]
> + * with length @len as shown below:
> + *
> + * 0 @env->buf[] @env->buflen
> + * ---------------------------------------------
> + * ^ ^ ^ ^
> + * | |-> @len <-| target block |
> + * @env->envp[0] @env->envp[i] @env->envp[i + 1]
> + *
> + * so the "target block" indicated above is moved
> + * backward by @len, and its right size is
> + * @env->buflen - (@env->envp[i + 1] - @env->envp[0]).
> + */
> memmove(env->envp[i], env->envp[i + 1],
> - env->buflen - len);
> + env->buflen - (env->envp[i + 1] - env->envp[0]));
>
> for (j = i; j < env->envp_idx - 1; j++)
> env->envp[j] = env->envp[j + 1] - len;

Reviewed-by: Lk Sii <[email protected]>