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

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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 <harshit.m.mogalapalli@xxxxxxxxxx>
---
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



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