2023-04-28 06:03:08

by Harshit Mogalapalli

Subject: [PATCH] module: Fix use-after-free bug in read_file_mod_stats()

Smatch warns:
kernel/module/stats.c:394 read_file_mod_stats()
warn: passing freed memory 'buf'

We are passing 'buf' to simple_read_from_buffer() after freeing it.

Fix this by changing the order of 'simple_read_from_buffer' and 'kfree'.

Fixes: df3e764d8e5c ("module: add debug stats to help identify memory pressure")
Signed-off-by: Harshit Mogalapalli <[email protected]>
---
Found with statis analysis, only compile tested.
---
kernel/module/stats.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/module/stats.c b/kernel/module/stats.c
index ad7b6ada29f2..6ab2c94d6bc3 100644
--- a/kernel/module/stats.c
+++ b/kernel/module/stats.c
@@ -276,6 +276,7 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
struct mod_fail_load *mod_fail;
unsigned int len, size, count_failed = 0;
char *buf;
+ int ret;
u32 live_mod_count, fkreads, fdecompress, fbecoming, floads;
unsigned long total_size, text_size, ikread_bytes, ibecoming_bytes,
idecompress_bytes, imod_bytes, total_virtual_lost;
@@ -390,8 +391,9 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
out_unlock:
mutex_unlock(&module_mutex);
out:
+ ret = simple_read_from_buffer(user_buf, count, ppos, buf, len);
kfree(buf);
- return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+ return ret;
}
#undef MAX_PREAMBLE
#undef MAX_FAILED_MOD_PRINT
--
2.40.0

2023-05-17 07:02:51

by Harshit Mogalapalli

Subject: Re: [PATCH] module: Fix use-after-free bug in read_file_mod_stats()

Hi,
On 28/04/23 11:29 am, Harshit Mogalapalli wrote:
> Smatch warns:
> kernel/module/stats.c:394 read_file_mod_stats()
> warn: passing freed memory 'buf'
>
> We are passing 'buf' to simple_read_from_buffer() after freeing it.
>
> Fix this by changing the order of 'simple_read_from_buffer' and 'kfree'.
>

Friendly reminder to review this patch.

Thanks,
Harshit


> Fixes: df3e764d8e5c ("module: add debug stats to help identify memory pressure")
> Signed-off-by: Harshit Mogalapalli <[email protected]>
> ---
> Found with statis analysis, only compile tested.
> ---
> kernel/module/stats.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/module/stats.c b/kernel/module/stats.c
> index ad7b6ada29f2..6ab2c94d6bc3 100644
> --- a/kernel/module/stats.c
> +++ b/kernel/module/stats.c
> @@ -276,6 +276,7 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
> struct mod_fail_load *mod_fail;
> unsigned int len, size, count_failed = 0;
> char *buf;
> + int ret;
> u32 live_mod_count, fkreads, fdecompress, fbecoming, floads;
> unsigned long total_size, text_size, ikread_bytes, ibecoming_bytes,
> idecompress_bytes, imod_bytes, total_virtual_lost;
> @@ -390,8 +391,9 @@ static ssize_t read_file_mod_stats(struct file *file, char __user *user_buf,
> out_unlock:
> mutex_unlock(&module_mutex);
> out:
> + ret = simple_read_from_buffer(user_buf, count, ppos, buf, len);
> kfree(buf);
> - return simple_read_from_buffer(user_buf, count, ppos, buf, len);
> + return ret;
> }
> #undef MAX_PREAMBLE
> #undef MAX_FAILED_MOD_PRINT

2023-05-22 21:35:09

by Luis Chamberlain

Subject: Re: [PATCH] module: Fix use-after-free bug in read_file_mod_stats()

On Thu, Apr 27, 2023 at 10:59:33PM -0700, Harshit Mogalapalli wrote:
> Smatch warns:
> kernel/module/stats.c:394 read_file_mod_stats()
> warn: passing freed memory 'buf'
>
> We are passing 'buf' to simple_read_from_buffer() after freeing it.
>
> Fix this by changing the order of 'simple_read_from_buffer' and 'kfree'.
>
> Fixes: df3e764d8e5c ("module: add debug stats to help identify memory pressure")
> Signed-off-by: Harshit Mogalapalli <[email protected]>
> ---

Queued up, thanks!

Luis