media: vidtv: fix nfeeds state corruption on start_streaming failure

In the Linux kernel, the following vulnerability has been resolved:

media: vidtv: fix nfeeds state corruption on start_streaming failure

syzbot reported a memory leak in vidtv_psi_service_desc_init [1].

When vidtv_start_streaming() fails inside vidtv_start_feed(), the

nfeeds counter is left incremented even though no feed was actually

started. This corrupts the driver state: subsequent start_feed calls

see nfeeds > 1 and skip starting the mux, while stop_feed calls

eventually try to stop a non-existent stream.

This state corruption can also lead to memory leaks, since the mux

and channel resources may be partially allocated during a failed

start_streaming but never cleaned up, as the stop path finds

dvb->streaming == false and returns early.

Fix by decrementing nfeeds back when start_streaming fails, keeping

the counter in sync with the actual number of active feeds.

[1]

BUG: memory leak

unreferenced object 0xffff888145b50820 (size 32):

comm "syz.0.17", pid 6068, jiffies 4294944486

backtrace (crc 90a0c7d4):

vidtv_psi_service_desc_init+0x74/0x1b0 drivers/media/test-drivers/vidtv/vidtv_psi.c:288

vidtv_channel_s302m_init+0xb1/0x2a0 drivers/media/test-drivers/vidtv/vidtv_channel.c:83

vidtv_channels_init+0x1b/0x40 drivers/media/test-drivers/vidtv/vidtv_channel.c:524

vidtv_mux_init+0x516/0xbe0 drivers/media/test-drivers/vidtv/vidtv_mux.c:518

vidtv_start_streaming drivers/media/test-drivers/vidtv/vidtv_bridge.c:194 [inline]

vidtv_start_feed+0x33e/0x4d0 drivers/media/test-drivers/vidtv/vidtv_bridge.c:239