jfs: fix null ptr deref in dtInsertEntry

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: jfs: fix null ptr deref in dtInsertEntry [syzbot reported] general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 5061 Comm: syz-executor404 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 RIP: 0010:dtInsertEntry+0xd0c/0x1780 fs/jfs/jfs_dtree.c:3713 ... [Analyze] In dtInsertEntry(), when the pointer h has the same value as p, after writing name in UniStrncpy_to_le(), p->header.flag will be cleared. This will cause the previously true judgment "p->header.flag & BT-LEAF" to change to no after writing the name operation, this leads to entering an incorrect branch and accessing the uninitialized object ih when judging this condition for the second time. [Fix] After got the page, check freelist first, if freelist == 0 then exit dtInsert() and return -EINVAL.

References

• https://git.kernel.org/stable/c/f98bf80b20f4a930589cda48a35f751a64fe0dc2
• https://git.kernel.org/stable/c/53023ab11836ac56fd75f7a71ec1356e50920fa9
• https://git.kernel.org/stable/c/6ea10dbb1e6c58384136e9adfd75f81951e423f6
• https://git.kernel.org/stable/c/9c2ac38530d1a3ee558834dfa16c85a40fd0e702
• https://git.kernel.org/stable/c/ce6dede912f064a855acf6f04a04cbb2c25b8c8c