linux-kernel - [PATCH] media: vidtv: fix read after free

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Message-Id: <20201130092825.28532-1-cengiz@kernel.wtf>
Date:   Mon, 30 Nov 2020 12:28:26 +0300
From:   Cengiz Can <cengiz@...nel.wtf>
To:     "Daniel W . S . Almeida" <dwlsalmeida@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Cengiz Can <cengiz@...nel.wtf>
Subject: [PATCH] media: vidtv: fix read after free

`vidtv_channel_si_destroy` function has a call to
    `vidtv_psi_pat_table_destroy` that frees Program Association Table.

However it is followed by a loop that iterates over the count of Program
Map Tables. This obviously accesses an invalid memory.

Eliminate this by making a copy of num_pmt before free'ing Program
Association Table and loop on it instead.

Signed-off-by: Cengiz Can <cengiz@...nel.wtf>
---
 drivers/media/test-drivers/vidtv/vidtv_channel.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/test-drivers/vidtv/vidtv_channel.c b/drivers/media/test-drivers/vidtv/vidtv_channel.c
index 8ad6c0744d36..4af39a8786a7 100644
--- a/drivers/media/test-drivers/vidtv/vidtv_channel.c
+++ b/drivers/media/test-drivers/vidtv/vidtv_channel.c
@@ -503,10 +503,13 @@ int vidtv_channel_si_init(struct vidtv_mux *m)
 void vidtv_channel_si_destroy(struct vidtv_mux *m)
 {
 	u32 i;
+	u16 num_pmt;
+
+	num_pmt = m->si.pat->num_pmt;
 
 	vidtv_psi_pat_table_destroy(m->si.pat);
 
-	for (i = 0; i < m->si.pat->num_pmt; ++i)
+	for (i = 0; i < num_pmt; ++i)
 		vidtv_psi_pmt_table_destroy(m->si.pmt_secs[i]);
 
 	kfree(m->si.pmt_secs);
-- 
2.29.2