misc: bcm_vk: Fix possible null-pointer dereferences in bcm_vk_read()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: misc: bcm_vk: Fix possible null-pointer dereferences in bcm_vk_read() In the function bcm_vk_read(), the pointer entry is checked, indicating that it can be NULL. If entry is NULL and rc is set to -EMSGSIZE, the following code may cause null-pointer dereferences: struct vk_msg_blk tmp_msg = entry->to_h_msg[0]; set_msg_id(&tmp_msg, entry->usr_msg_id); tmp_msg.size = entry->to_h_blks - 1; To prevent these possible null-pointer dereferences, copy to_h_msg, usr_msg_id, and to_h_blks from iter into temporary variables, and return these temporary variables to the application instead of accessing them through a potentially NULL entry.

References

• https://git.kernel.org/stable/c/741c5a3a0cd893a4218fc0fc8c18403e54fcfb22
• https://git.kernel.org/stable/c/ece3722169ba93734bfd1f06255e8ab7f19fe964
• https://git.kernel.org/stable/c/aa97ccc3dc1eba9f4537f0410e9dbb0b05ccf2fb
• https://git.kernel.org/stable/c/3842f93e6e29d5cc1dcb9e5bda70587b444bed69
• https://git.kernel.org/stable/c/20f2d9dbe5e972516f8f9948d7ae5b95d1ad77bd
• https://git.kernel.org/stable/c/ba75ecb97d3f4e95d59002c13afb6519205be6cb