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

media: vidtv: fix NULL pointer dereference in vidtv_mux_push_si

syzbot reported a general protection fault in
vidtv_psi_ts_psi_write_into [1].

vidtv_mux_get_pid_ctx() can return NULL, but vidtv_mux_push_si() does
not check for this before dereferencing the returned pointer to access
the continuity counter. This leads to a general protection fault when
accessing a near-NULL address.

The root cause is that vidtv_mux_pid_ctx_init() does not check the
return value of vidtv_mux_create_pid_ctx_once() for PMT section PIDs.
If the allocation fails, the PID context is never created, but init
returns success. The subsequent vidtv_mux_push_si() call then gets
NULL from vidtv_mux_get_pid_ctx() and crashes.

Fix both the root cause (add error check in vidtv_mux_pid_ctx_init
for PMT PIDs) and add defensive NULL checks in vidtv_mux_push_si for
all vidtv_mux_get_pid_ctx() calls.

[1]
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
Workqueue: events vidtv_mux_tick
RIP: 0010:vidtv_psi_ts_psi_write_into+0x54a/0xbc0 drivers/media/test-drivers/vidtv/vidtv_psi.c:197
Call Trace:
 <TASK>
 vidtv_psi_table_header_write_into drivers/media/test-drivers/vidtv/vidtv_psi.c:799 [inline]
 vidtv_psi_pmt_write_into+0x3b2/0xa70 drivers/media/test-drivers/vidtv/vidtv_psi.c:1231
 vidtv_mux_push_si+0x932/0xe80 drivers/media/test-drivers/vidtv/vidtv_mux.c:196
 vidtv_mux_tick+0xe9b/0x1480 drivers/media/test-drivers/vidtv/vidtv_mux.c:408

https://git.kernel.org/stable/c/232e4b313ea342672edf8947e067c0de4328405b

https://git.kernel.org/stable/c/353d9578951dd38bc9679308f5b618ceed1f20fa

https://git.kernel.org/stable/c/455bc12e7b73ab5a2dfcb47822e91e772bc6c42e

https://git.kernel.org/stable/c/6df7e16d4f742c80add58995a6e69385b97aa9e6

https://git.kernel.org/stable/c/7d8bf3d8f91073f4db347ed3aa6302b56107499c

https://git.kernel.org/stable/c/b28b12be6e8910489e6800ed93ea4d41dfe19683

https://git.kernel.org/stable/c/cd923dadefadb9671b5ac341b672ff424d429c39

https://git.kernel.org/stable/c/f0f5a1d7056980a0d512456fdb370cfb72bba86a

https://git.kernel.org/stable/c/f965cf22dda7f512f4922415894c3e528269a4ae

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