driver: iio: add missing checks on iio_info's callback access

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: driver: iio: add missing checks on iio_info's callback access Some callbacks from iio_info structure are accessed without any check, so if a driver doesn't implement them trying to access the corresponding sysfs entries produce a kernel oops such as: [ 2203.527791] Unable to handle kernel NULL pointer dereference at virtual address 00000000 when execute [...] [ 2203.783416] Call trace: [ 2203.783429] iio_read_channel_info_avail from dev_attr_show+0x18/0x48 [ 2203.789807] dev_attr_show from sysfs_kf_seq_show+0x90/0x120 [ 2203.794181] sysfs_kf_seq_show from seq_read_iter+0xd0/0x4e4 [ 2203.798555] seq_read_iter from vfs_read+0x238/0x2a0 [ 2203.802236] vfs_read from ksys_read+0xa4/0xd4 [ 2203.805385] ksys_read from ret_fast_syscall+0x0/0x54 [ 2203.809135] Exception stack(0xe0badfa8 to 0xe0badff0) [ 2203.812880] dfa0: 00000003 b6f10f80 00000003 b6eab000 00020000 00000000 [ 2203.819746] dfc0: 00000003 b6f10f80 7ff00000 00000003 00000003 00000000 00020000 00000000 [ 2203.826619] dfe0: b6e1bc88 bed80958 b6e1bc94 b6e1bcb0 [ 2203.830363] Code: bad PC value [ 2203.832695] ---[ end trace 0000000000000000 ]---

References

• https://git.kernel.org/stable/c/2b961d5786b4b31c367c719a2f918569b444c007
• https://git.kernel.org/stable/c/0cc7e0ee31e5c44904e98e2229d591e093282a70
• https://git.kernel.org/stable/c/72f022ebb9deac28663fa4c04ba315ed5d6654d1
• https://git.kernel.org/stable/c/dc537a72f64890d883d24ae4ac58733fc5bc523d
• https://git.kernel.org/stable/c/c4ec8dedca961db056ec85cb7ca8c9f7e2e92252